Quantum dot LED is a new technology for producing displays. Quantum dots: printing and other applications

Numerous spectroscopic methods that appeared in the second half of the 20th century - electron and atomic force microscopy, nuclear magnetic resonance spectroscopy, mass spectrometry - it would seem that traditional optical microscopy was “retired” long ago. However, the skillful use of the fluorescence phenomenon more than once extended the “veteran’s” life. This article will talk about quantum dots(fluorescent semiconductor nanocrystals), which breathed new strength into optical microscopy and made it possible to look beyond the notorious diffraction limit. Unique physical properties Quantum dots make them an ideal tool for ultrasensitive multicolor recording of biological objects, as well as for medical diagnostics.

The work gives ideas about physical principles, defining the unique properties of quantum dots, the main ideas and prospects for the use of nanocrystals, and describes the already achieved successes in their use in biology and medicine. The article is based on the results of research conducted in last years at the Laboratory of Molecular Biophysics of the Institute of Bioorganic Chemistry named after. MM. Shemyakin and Yu.A. Ovchinnikov together with the University of Reims and the Belarusian State University, aimed at developing a new generation of biomarker technology for various areas of clinical diagnostics, including cancer and autoimmune diseases, as well as creating new types of nanosensors for the simultaneous recording of many biomedical parameters. The original version of the work was published in Nature; to some extent, the article is based on the second seminar of the Council of Young Scientists of the IBCh RAS. - Ed.

Part I, theoretical

Figure 1. Discrete energy levels in nanocrystals."Solid" semiconductor ( left) has a valence band and a conduction band separated by a band gap E g. Semiconductor nanocrystal ( on right) is characterized by discrete energy levels, similar to the energy levels of a single atom. In a nanocrystal E g is a function of size: an increase in the size of a nanocrystal leads to a decrease E g.

Reducing the particle size leads to the manifestation of very unusual properties of the material from which it is made. The reason for this is quantum mechanical effects that arise when the movement of charge carriers is spatially limited: the energy of the carriers in this case becomes discrete. And the number of energy levels, as taught quantum mechanics, depends on the size of the “potential well”, the height of the potential barrier and the mass of the charge carrier. An increase in the size of the “well” leads to an increase in the number of energy levels, which become increasingly closer to each other until they merge and the energy spectrum becomes “solid” (Fig. 1). The movement of charge carriers can be limited along one coordinate (forming quantum films), along two coordinates (quantum wires or threads) or in all three directions - these will be quantum dots(CT).

Semiconductor nanocrystals are intermediate structures between molecular clusters and “solid” materials. The boundaries between molecular, nanocrystalline and solid materials are not clearly defined; however, the range of 100 ÷ 10,000 atoms per particle can be tentatively considered the “upper limit” of nanocrystals. The upper limit corresponds to sizes for which the interval between energy levels exceeds the energy of thermal vibrations kT (k- Boltzmann constant, T- temperature) when charge carriers become mobile.

The natural length scale for electronic excited regions in "continuous" semiconductors is determined by the Bohr exciton radius a x, which depends on the strength of the Coulomb interaction between the electron ( e) And hole (h). In nanocrystals of the order of magnitude a x the size itself begins to influence the configuration of the couple e–h and hence the size of the exciton. It turns out that in this case, electronic energies are directly determined by the size of the nanocrystal - this phenomenon is known as the “quantum confinement effect.” Using this effect, it is possible to regulate the band gap of the nanocrystal ( E g), simply by changing the particle size (Table 1).

Unique properties of quantum dots

As a physical object, quantum dots have been known for quite a long time, being one of the forms that are being intensively developed today. heterostructures. The peculiarity of quantum dots in the form of colloidal nanocrystals is that each dot is an isolated and mobile object located in a solvent. Such nanocrystals can be used to construct various associates, hybrids, ordered layers, etc., on the basis of which elements of electronic and optoelectronic devices, probes and sensors for analysis in microvolumes of matter, various fluorescent, chemiluminescent and photoelectrochemical nanosized sensors are constructed.

The reason for the rapid penetration of semiconductor nanocrystals into a variety of different areas science and technology are their unique optical characteristics:

• narrow symmetrical fluorescence peak (unlike organic dyes, which are characterized by the presence of a long-wave “tail”; Fig. 2, left), the position of which is controlled by the choice of nanocrystal size and its composition (Fig. 3);
• wide excitation band, which makes it possible to excite nanocrystals of different colors with one radiation source (Fig. 2, left). This advantage is fundamental when creating multicolor coding systems;
• high fluorescence brightness, determined by a high extinction value and high quantum yield (for CdSe/ZnS nanocrystals - up to 70%);
• uniquely high photostability (Fig. 2, on right), which allows the use of high power excitation sources.

Figure 2. Spectral properties of cadmium-selenium (CdSe) quantum dots. Left: Nanocrystals of different colors can be excited by a single source (the arrow indicates excitation with an argon laser with a wavelength of 488 nm). The inset shows the fluorescence of CdSe/ZnS nanocrystals of different sizes (and, accordingly, colors) excited by a single light source (UV lamp). On right: Quantum dots are extremely photostable compared to other common dyes, which quickly degrade under the beam of a mercury lamp in a fluorescence microscope.

Figure 3. Properties of quantum dots from different materials. Above: Fluorescence ranges of nanocrystals made from different materials. Bottom: CdSe quantum dots of different sizes cover the entire visible range of 460–660 nm. Bottom right: Diagram of a stabilized quantum dot, where the “core” is covered with a semiconductor shell and protective layer polymer.

Receiving technology

The synthesis of nanocrystals is carried out by rapid injection of precursor compounds into the reaction medium at high temperature (300–350 °C) and subsequent slow growth nanocrystals at relatively low temperatures (250–300 °C). In the “focusing” synthesis mode, the growth rate of small particles is greater than the growth rate of large ones, as a result of which the spread in nanocrystal sizes decreases.

Controlled synthesis technology makes it possible to control the shape of nanoparticles using the anisotropy of nanocrystals. The characteristic crystal structure of a particular material (for example, CdSe is characterized by hexagonal packing - wurtzite, Fig. 3) mediates “preferred” growth directions that determine the shape of nanocrystals. This is how nanorods or tetrapods are obtained - nanocrystals elongated in four directions (Fig. 4).

Figure 4. Different shape CdSe nanocrystals. Left: CdSe/ZnS spherical nanocrystals (quantum dots); in the center: rod-shaped (quantum rods). On right: in the form of tetrapods. (Transmission electron microscopy. Mark - 20 nm.)

Barriers to practical application

There are a number of restrictions on the practical application of nanocrystals made from group II–VI semiconductors. Firstly, their luminescence quantum yield significantly depends on the properties of the environment. Secondly, the stability of the “nuclei” of nanocrystals in aqueous solutions is also low. The problem lies in surface “defects” that play the role of non-radiative recombination centers or “traps” for excited e–h steam.

To overcome these problems, quantum dots are encased in a shell consisting of several layers of wide-gap material. This allows you to isolate e-h pair in the nucleus, increase its lifetime, reduce non-radiative recombination, and therefore increase the quantum yield of fluorescence and photostability.

In this regard, to date, the most widely used fluorescent nanocrystals have a core/shell structure (Fig. 3). Developed procedures for the synthesis of CdSe/ZnS nanocrystals make it possible to achieve a quantum yield of 90%, which is close to the best organic fluorescent dyes.

Part II: Applications of Quantum Dots in the Form of Colloidal Nanocrystals

Fluorophores in medicine and biology

The unique properties of QDs make it possible to use them in almost all systems for labeling and visualizing biological objects (with the exception of only fluorescent intracellular labels, genetically expressed - well-known fluorescent proteins).

To visualize biological objects or processes, QDs can be introduced into the object directly or with “sewn” recognition molecules (usually antibodies or oligonucleotides). Nanocrystals penetrate and distribute throughout the object in accordance with their properties. For example, nanocrystals of different sizes penetrate biological membranes in different ways, and since size determines the color of fluorescence, different areas of the object are also colored differently (Fig. 5). The presence of recognition molecules on the surface of nanocrystals allows for targeted binding: the desired object (for example, a tumor) is painted with a given color!

Figure 5. Coloring objects. Left: multicolor confocal fluorescent image of the distribution of quantum dots against the background of the microstructure of the cellular cytoskeleton and nucleus in human phagocyte THP-1 cells. Nanocrystals remain photostable in cells for at least 24 hours and do not cause disruption of cell structure and function. On right: accumulation of nanocrystals “cross-linked” with RGD peptide in the tumor area (arrow). To the right is the control, nanocrystals without peptide were introduced (CdTe nanocrystals, 705 nm).

Spectral coding and “liquid microchips”

As already indicated, the fluorescence peak of nanocrystals is narrow and symmetrical, which makes it possible to reliably isolate the fluorescence signal of nanocrystals of different colors (up to ten colors in the visible range). On the contrary, the absorption band of nanocrystals is wide, that is, nanocrystals of all colors can be excited by a single light source. These properties, as well as their high photostability, make quantum dots ideal fluorophores for multicolor spectral coding of objects - similar to a bar code, but using multicolor and "invisible" codes that fluoresce in the infrared region.

Currently, the term “liquid microchips” is increasingly used, which allows, like classic flat chips, where detecting elements are located on a plane, to carry out analysis of many parameters simultaneously using microvolumes of a sample. The principle of spectral coding using liquid microchips is illustrated in Figure 6. Each microchip element contains specified quantities of QDs of certain colors, and the number of encoded options can be very large!

Figure 6. Spectral coding principle. Left:"regular" flat microchip. On right:“liquid microchip”, each element of which contains specified quantities of QDs of certain colors. At n fluorescence intensity levels and m colors, the theoretical number of encoded options is n m−1. So, for 5–6 colors and 6 intensity levels, this will be 10,000–40,000 options.

Such encoded microelements can be used for direct tagging of any objects (for example, securities). When embedded in polymer matrices, they are extremely stable and durable. Another aspect of application is the identification of biological objects in the development of early diagnostic methods. The indication and identification method is that a specific recognition molecule is attached to each spectrally encoded element of the microchip. There is a second recognition molecule in the solution, to which a signal fluorophore is “sewn”. The simultaneous appearance of microchip fluorescence and a signal fluorophore indicates the presence of the studied object in the analyzed mixture.

Flow cytometry can be used to analyze encoded microparticles on-line. A solution containing microparticles passes through a laser-irradiated channel, where each particle is characterized spectrally. Software The device allows you to identify and characterize events associated with the appearance of certain compounds in a sample - for example, markers of cancer or autoimmune diseases.

In the future, microanalyzers can be created based on semiconductor fluorescent nanocrystals to simultaneously record a huge number of objects.

Molecular sensors

The use of QDs as probes makes it possible to measure environmental parameters in local areas, the size of which is comparable to the size of the probe (nanometer scale). The action of such measuring instruments It is based on the use of the Förster resonanse energy transfer - FRET effect. The essence of the FRET effect is that when two objects (donor and acceptor) approach and overlap fluorescence spectrum first from absorption spectrum second, energy is transferred non-radiatively - and if the acceptor can fluoresce, it will glow with double the intensity.

We have already written about the FRET effect in the article “ Roulette for spectroscopist » .

Three parameters of quantum dots make them very attractive donors in FRET-format systems.

1. Possibility with high accuracy select the emission wavelength to obtain maximum overlap donor emission spectra and acceptor excitation spectra.
2. The ability to excite different QDs with the same wavelength of a single light source.
3. Possibility of excitation in a spectral region far from the emission wavelength (difference >100 nm).

There are two strategies for using the FRET effect:

• registration of the act of interaction between two molecules due to conformational changes in the donor-acceptor system and
• registration of changes optical properties donor or acceptor (for example, absorption spectrum).

This approach made it possible to implement nanosized sensors for measuring pH and the concentration of metal ions in a local region of the sample. The sensitive element in such a sensor is a layer of indicator molecules that change optical properties when bound to the detected ion. As a result of binding, the overlap between the fluorescence spectra of the QD and the absorption spectra of the indicator changes, which also changes the efficiency of energy transfer.

An approach using conformational changes in the donor-acceptor system is implemented in a nanoscale temperature sensor. The action of the sensor is based on a temperature change in the shape of the polymer molecule connecting the quantum dot and the acceptor - fluorescence quencher. When the temperature changes, both the distance between the quencher and the fluorophore and the intensity of fluorescence, from which a conclusion about the temperature, changes.

Molecular diagnostics

The breaking or formation of a bond between a donor and an acceptor can be detected in the same way. Figure 7 demonstrates the “sandwich” registration principle, in which the registered object acts as a connecting link (“adapter”) between the donor and the acceptor.

Figure 7. Principle of registration using the FRET format. The formation of a conjugate (“liquid microchip”)-(registered object)-(signal fluorophore) brings the donor (nanocrystal) closer to the acceptor (AlexaFluor dye). By itself laser radiation does not excite dye fluorescence; the fluorescent signal appears only due to resonant energy transfer from the CdSe/ZnS nanocrystal. Left: structure of a conjugate with energy transfer. On right: spectral diagram of dye excitation.

An example of the implementation of this method is the creation of a diagnostic kit for an autoimmune disease systemic scleroderma(scleroderma). Here, the donor was quantum dots with a fluorescence wavelength of 590 nm, and the acceptor was an organic dye - AlexaFluor 633. An antigen was “sewn” onto the surface of a microparticle containing quantum dots to an autoantibody - a marker of scleroderma. Secondary antibodies labeled with dye were introduced into the solution. In the absence of a target, the dye does not approach the surface of the microparticle, there is no energy transfer and the dye does not fluoresce. But if autoantibodies appear in the sample, this leads to the formation of a microparticle-autoantibody-dye complex. As a result of energy transfer, the dye is excited, and its fluorescence signal with a wavelength of 633 nm appears in the spectrum.

The importance of this work is also that autoantibodies can be used as diagnostic markers at the very early stages of the development of autoimmune diseases. “Liquid microchips” make it possible to create test systems in which antigens are located in much more natural conditions, rather than on a plane (as in “regular” microchips). The results already obtained pave the way for the creation of a new type of clinical diagnostic tests based on the use of quantum dots. And the implementation of approaches based on the use of spectrally encoded liquid microchips will make it possible to simultaneously determine the content of many markers at once, which is the basis for a significant increase in the reliability of diagnostic results and the development of early diagnostic methods.

Hybrid molecular devices

The ability to flexibly control the spectral characteristics of quantum dots opens the way to nanoscale spectral devices. In particular, cadmium-tellurium (CdTe)-based QDs have made it possible to expand the spectral sensitivity bacteriorhodopsin(bP), known for its ability to use light energy to “pump” protons across a membrane. (The resulting electrochemical gradient is used by bacteria to synthesize ATP.)

In fact, a new hybrid material has been obtained: attaching quantum dots to purple membrane- a lipid membrane containing densely packed bacteriorhodopsin molecules - expands the range of photosensitivity to the UV and blue regions of the spectrum, where “ordinary” bP does not absorb light (Fig. 8). The mechanism of energy transfer to bacteriorhodopsin from a quantum dot that absorbs light in the UV and blue regions is still the same: it is FRET; The radiation acceptor in this case is retinal- the same pigment that works in the photoreceptor rhodopsin.

Figure 8. “Upgrade” of bacteriorhodopsin using quantum dots. Left: a proteoliposome containing bacteriorhodopsin (in the form of trimers) with CdTe-based quantum dots “sewn” to it (shown as orange spheres). On right: scheme for expanding the spectral sensitivity of bR due to CT: area on the spectrum takeovers QD is in the UV and blue parts of the spectrum; range emissions can be “tuned” by choosing the size of the nanocrystal. However, in this system, energy is not emitted by quantum dots: the energy non-radiatively migrates to bacteriorhodopsin, which does work (pumps H + ions into the liposome).

Proteoliposomes (lipid “vesicles” containing a bP-QD hybrid) created on the basis of such material pump protons into themselves when illuminated, effectively lowering the pH (Fig. 8). This seemingly insignificant invention may in the future form the basis of optoelectronic and photonic devices and find application in the field of electric power and other types of photoelectric conversions.

To summarize, it should be emphasized that quantum dots in the form of colloidal nanocrystals are the most promising objects of nano-, bionano- and biocopper-nanotechnologies. After the first demonstration of the capabilities of quantum dots as fluorophores in 1998, there was a lull for several years associated with the formation of new original approaches to the use of nanocrystals and the realization of the potential capabilities that these unique objects possess. But in recent years, there has been a sharp rise: the accumulation of ideas and their implementations have determined a breakthrough in the creation of new devices and tools based on the use of semiconductor nanocrystalline quantum dots in biology, medicine, electronic engineering, technology of use solar energy and many others. Of course there is still a lot on this path unresolved problems, but growing interest, a growing number of teams working on these problems, and a growing number of publications devoted to this area allow us to hope that quantum dots will become the basis of the next generation of equipment and technologies.

Video recording of V.A.’s speech Oleynikova at the second seminar of the Council of Young Scientists of the IBCh RAS, held on May 17, 2012.

Literature

1. Oleynikov V.A. (2010). Quantum dots in biology and medicine. Nature. 3 , 22;
2. Oleynikov V.A., Sukhanova A.V., Nabiev I.R. (2007). Fluorescent semiconductor nanocrystals in biology and medicine. Russian nanotechnologies. 2 , 160–173;
3. Alyona Sukhanova, Lydie Venteo, Jérôme Devy, Mikhail Artemyev, Vladimir Oleinikov, et. al.. (2002). Highly Stable Fluorescent Nanocrystals as a Novel Class of Labels for Immunohistochemical Analysis of Paraffin-Embedded Tissue Sections. Lab Invest. 82 , 1259-1261;
4. C. B. Murray, D. J. Norris, M. G. Bawendi. (1993). Synthesis and characterization of nearly monodisperse CdE (E = sulfur, selenium, tellurium) semiconductor nanocrystallites. J. Am. Chem. Soc.. 115 , 8706-8715;
5. Margaret A. Hines, Philippe Guyot-Sionnest. (1998). Bright UV-Blue Luminescent Colloidal ZnSe Nanocrystals. J. Phys. Chem. B. 102 , 3655-3657;
6. Manna L., Scher E.C., Alivisatos P.A. (2002). Shape control of colloidal semiconductor nanocrystals. J. Clust. Sci. 13 , 521–532;
7. Fluorescent Nobel Prize in Chemistry;
8. Igor Nabiev, Siobhan Mitchell, Anthony Davies, Yvonne Williams, Dermot Kelleher, et. al.. (2007). Nonfunctionalized Nanocrystals Can Exploit a Cell's Active Transport Machinery Delivering Them to Specific Nuclear and Cytoplasmic Compartments. Nano Lett.. 7 , 3452-3461;
9. Yvonne Williams, Alyona Sukhanova, MaÅgorzata Nowostawska, Anthony M. Davies, Siobhan Mitchell, et. al.. (2009). Probing Cell-Type-Specific Intracellular Nanoscale Barriers Using Size-Tuned Quantum Dots Nano-pH Meter;
10. Alyona Sukhanova, Andrei S. Susha, Alpan Bek, Sergiy Mayilo, Andrey L. Rogach, et. al.. (2007). Nanocrystal-Encoded Fluorescent Microbeads for Proteomics: Antibody Profiling and Diagnostics of Autoimmune Diseases. Nano Lett.. 7 , 2322-2327;
11. Aliaksandra Rakovich, Alyona Sukhanova, Nicolas Bouchonville, Evgeniy Lukashev, Vladimir Oleinikov, et. al.. (2010). Resonance Energy Transfer Improves the Biological Function of Bacteriorhodopsin within a Hybrid Material Built from Purple Membranes and Semiconductor Quantum Dots. Nano Lett.. 10 , 2640-2648;

« Quantum dots are artificial atoms whose properties can be controlled»

Zh.I. Alferov, Nobel Prize laureate 2000. in physics for the development of semiconductor heterostructures for high-speed and optoelectronics

Quantum dots (QDs) are isolated nanoobjects whose properties differ significantly from the properties of bulk material of the same composition. It should be noted right away that quantum dots are more of a mathematical model than real objects. And this is due to the impossibility of completely forming isolated structures - small particles always interact with the environment, being in liquid medium or solid matrix.

To understand what quantum dots are and their electronic structure, imagine an ancient Greek amphitheater. Now imagine that an exciting performance is unfolding on stage, and the audience is filled with people who have come to watch the actors play. So it turns out that the behavior of people in the theater is in many ways similar to the behavior of quantum dot (QD) electrons. During the performance, the actors move around the arena without going into the audience, and the spectators themselves watch the action from their seats and do not go down to the stage. The arena is the lower filled levels of the quantum dot, and the spectator rows are the excited electronic levels with higher energy. In this case, just as a viewer can be in any row of the hall, an electron can occupy any energy level of a quantum dot, but cannot be located between them. When buying tickets for the performance at the box office, everyone tried to get the best seats - as close to the stage as possible. Indeed, who wants to sit in the last row, where you can’t see the actor’s face even with binoculars! Therefore, when the audience is seated before the start of the performance, all the lower rows of the hall are filled, just as in the stationary state of the CT, which has the lowest energy, the lower energy levels are completely occupied by electrons. However, during the performance, one of the spectators may leave his seat, for example, because the music on stage is playing too loudly or he just got caught by an unpleasant neighbor, and move to a free top row. This is how, in a quantum dot, an electron, under the influence of an external influence, is forced to move to a higher energy level that is not occupied by other electrons, leading to the formation of an excited state of a quantum dot. You are probably wondering what happens to that empty space on the energy level where the electron used to be - the so-called hole? It turns out that, through charge interactions, the electron remains connected to it and can go back at any moment, just as a spectator who has moved can always change his mind and return to the place indicated on his ticket. An electron-hole pair is called an “exciton” from the English word “excited”, which means “excited”. Migration between energy levels of a QD, similar to the ascent or descent of one of the spectators, is accompanied by a change in the energy of the electron, which corresponds to the absorption or emission of a quantum of light (photon) when the electron moves to a higher or higher level, respectively. low level. The behavior of electrons in a quantum dot described above leads to a discrete energy spectrum that is uncharacteristic of macro-objects, for which QDs are often called artificial atoms in which electron levels are discrete.

The strength (energy) of the connection between a hole and an electron determines the exciton radius, which is a characteristic value for each substance. If the particle size is smaller than the exciton radius, then the exciton is limited in space by its size, and the corresponding binding energy changes significantly compared to bulk matter (see “quantum-size effect”). It is not difficult to guess that if the exciton energy changes, then the energy of the photon emitted by the system when the excited electron moves to its original place also changes. Thus, obtaining monodisperse colloidal solutions of nanoparticles various sizes, transition energies can be controlled over a wide range of the optical spectrum.

The first quantum dots were metal nanoparticles, which were synthesized back in ancient Egypt for coloring various glasses (by the way, the ruby ​​stars of the Kremlin were obtained using a similar technology), although more traditional and widely known QDs are GaN semiconductor particles grown on substrates and colloidal solutions of CdSe nanocrystals. At the moment, there are many ways to obtain quantum dots; for example, they can be “cut” from thin layers semiconductor “heterostructures” using “nanolithography”, or can be spontaneously formed in the form of nano-sized inclusion structures semiconductor material one type in the matrix of another. Using the “molecular beam epitaxy” method, with a significant difference in the parameters of the unit cell of the substrate and the deposited layer, it is possible to achieve the growth of pyramidal quantum dots on the substrate, for the study of the properties of which Academician Zh.I. Alferov was awarded Nobel Prize. By controlling the conditions of the synthesis processes, it is theoretically possible to obtain quantum dots of certain sizes with specified properties.

Quantum dots are still a “young” object of research, but the broad prospects for their use in the design of lasers and displays of a new generation are already quite obvious. The optical properties of QDs are used in the most unexpected areas of science, which require tunable luminescent properties of the material; for example, in medical research, it is possible to “illuminate” diseased tissues with their help. People dreaming of “quantum computers” see quantum dots as promising candidates for building qubits.

Literature

N. Kobayashi. Introduction to nanotechnology. M.: BINOM. Knowledge Laboratory, 2007, 134 p.

V.Ya. Demikhovsky, G.A. Wugalter Physics of quantum low-dimensional structures. M.: Logos, 2000.

"Professor Pankov's Glasses" - portable device quantum restoration and iridoreflexotherapy. The main purpose of the device is the treatment and necessary prevention of diseases of the eyes, internal organs, and systems of the human body. Created by prof. The Pankov device is widely used in medical hospitals, outpatient clinics, and also independently at home.

"Pankov's glasses" will be useful to people whose work activity inseparable from the high load on the organ of vision (office workers, research fellows, managers, programmers, teachers, writers, drivers of all types of transport, etc.).

Specifications

The device is a spectacle frame in which LED emitters are mounted, controlled by built-in microprocessor controllers. The device's power supply is combined with LED emitters. Number of emitters - 2 pieces. Radiation wavelengths are 450, 530 and 650 nm. The outgoing radiation has a pulse-periodic operating mode. Power is supplied by 4 button batteries (AG-13). Power consumption - up to 0.1 W. The device is lightweight - approximately 200 grams.

The “Professor Pankov Glasses” device is supplied in the following set:

• Device "Pankov's glasses".
• Technical data sheet, instructions for use.
• Packaging box.

Operating principle

Exposure to light pulses on the eyes causes the pupils to contract and dilate reflexively, providing a unique healing effect. Thanks to it, spasms are relieved and, over time, the strength of the accommodative muscle increases. The rhythmic contraction of the eye muscles under the influence of the device activates lymphatic drainage, increasing blood circulation in the organ of vision, improves microcirculation in the tissues of the eye, including the retina, which makes their nutrition complete and correct. In addition, light exposure activates the process of neural transmission of signals and their visual perception.

The action of the device changes the diameter of the pupil, and at the same time the position of the iris changes, resulting in improved movement of intraocular fluid along the outflow paths. The liquid enters the anterior chamber enriched, saturating it nutrients. This improves the nutrition of the anterior ocular segment (cornea, iris, lens), which makes “Pankov Glasses” practically indispensable for pathologies of these structures of the organ of vision.

Indications

• initial degrees of cataract;
• retinal dystrophy;
• glaucoma;
• amblyopia, ;
• myopia (progressive);
• age;
• optic nerve atrophy;
• computer syndrome;
• period after ophthalmological operations.

Mode of application

Sessions with the device must be performed lying down or sitting. Before you start, you should do a simple breathing exercise (deep inhalations and exhalations).

You cannot conduct sessions while watching TV, or just before bed. It is not recommended to use the device in a state of irritation or increased nervousness.

Quantum exposure session time is fifteen minutes daily.

The first session should begin with your eyes closed (like each subsequent one) and last up to three minutes, which is necessary so that the intensity of the effect increases gradually. Each subsequent session is extended by 3 minutes. The maximum possible exposure time is 15 minutes. The course of treatment includes 15 sessions. It can be repeated no earlier than a month later.

In the case of eye fatigue syndrome, sessions should be conducted as needed for three minutes (daily) before starting work that causes eye fatigue, as well as after it.

The result of using the device will be much better if you use “Pankov Glasses” simultaneously with eye vitamins in capsules (Lutein Complex or Anthocyan Forte), as well as vitamin drops (Taufon, Quinax, etc.).

It is not recommended to interrupt sessions for more than three days.

Contraindications to the use of glasses

• inflammation of the eyes in the acute phase;
• retina;
• pregnancy;
• neoplasms of the brain and eyes;
• period after transplantation;
• age up to three years;
• chronic mental disorders;
• uncompensated diabetes;
• hypotension;
• stroke.

Price of the device, where to buy

Any substance of microscopic size is a nanoparticle, a material used by nanotechnology researchers to design and create new technologies based on the use of elements in this tiny form. We read carefully, because we will need to delve a little into the essence of the text.

Quantum dots are nanoparticles made from any semiconductor material, such as silicon, cadmium selenide, cadmium sulfide, or indium arsenide, that glow a specific color when illuminated with light.

The color they glow depends on the size of the nanoparticle. By placing quanta different sizes It is possible to achieve the presence of red, green and blue in every pixel of the display screen, which makes it possible to create a full spectrum of colors in these pixels (any existing color is created by mixing these colors).

When quantum dots are illuminated with UV light, some of the electrons gain enough energy to break free from the atoms. This ability allows them to move around the nanoparticle, creating a conduction zone in which electrons can freely move through the material and conduct electricity.

When electrons descend into the outer orbit around an atom (valence band), they emit light. The color of this light depends on the energy difference between the conduction band and the valence band.

The smaller the nanoparticle, the higher the energy difference between the valence band and the conduction band, resulting in a deeper blue color. For a larger nanoparticle, the energy difference between the valence band and the conduction band is lower, which shifts the emission toward the red.

Quantum dots and displays

For LCD displays, the benefits are numerous. Let's look at the most important and interesting features, which received LCD screens from quantum dots.

Higher peak brightness

One of the reasons why manufacturers are so excited about quantum dots is the ability to create screens with much higher peak brightness than using other technologies. In turn, the increased peak brightness gives much great opportunities to use HDR and Dolby Vision.

Dolby Vision is a video standard that has high dynamic range, that is, a very large difference in light between the brightest and darkest point on the screen, which makes the image more realistic and contrasty.

If you don’t know, developers are constantly trying to play the Lord God and create what he created (or who created all this around us, maybe the universe?), only to transfer it to the screen.

That is, for example, normal sky on a clear day has a brightness of approximately 20,000 nits (brightness unit), while best tvs can provide brightness of about 10 less. So, the Dolby Vision standard is still ahead of the rest, but they are still very far from the Creator :)

Accordingly, quantum dot screens are another step towards a brighter image. Perhaps someday we will be able to see an almost real sunrise and/or sunset, and maybe other unique wonders of nature, without leaving home.

Best color rendition

Another big benefit of quantum dots is improved color accuracy. Since each pixel contains CTs of red, blue and green, it gives you access to a full palette of colors, which in turn allows you to achieve an incredible number of shades of any color.

Improved battery life for mobile devices

Quantum dot screens promise not only excellent image quality, but also extremely low power consumption.

Quantum dots and Samsung QLED

TVs based on quantum dots from Samsung, or simply, are actually not entirely based on quantum dots in the correct understanding of this technology. QLED is more of a hybrid, something between quantum dots and LED screens. Why? Because these TVs still use LED backlighting, and in a real quantum dot screen, the light must be created by the dots.

Therefore, even if the new TVs from the South Korean giant show better than conventional LED screens, they are still not quantum dot TVs, but TVs with quantum dots instead of a light filter.

Comments:

June 14th, 2018

A quantum dot is a fragment of a conductor or semiconductor whose charge carriers (electrons or holes) are limited in space in all three dimensions. The size of the quantum dot must be so small that quantum effects were significant. This is achieved if kinetic energy electron is noticeably greater than all other energy scales: first of all, greater than the temperature expressed in energy units. Quantum dots were first synthesized in the early 1980s by Alexei Ekimov in a glass matrix and by Louis E. Brous in colloidal solutions.

The term "quantum dot" was coined by Mark Reed.

The energy spectrum of a quantum dot is discrete, and the distance between stationary energy levels of the charge carrier depends on the size of the quantum dot itself as - ħ/(2md^2), where:
ħ—reduced Planck constant;
d is the characteristic size of the point;
m is the effective mass of an electron at a point

In simple terms, a quantum dot is a semiconductor whose electrical characteristics depend on its size and shape.
For example, when an electron moves to a lower energy level, a photon is emitted; Since you can adjust the size of a quantum dot, you can also change the energy of the emitted photon, and therefore change the color of the light emitted by the quantum dot.

Types of Quantum Dots
There are two types:
epitaxial quantum dots;
colloidal quantum dots.

In fact, they are named after the methods used to obtain them. I will not talk about them in detail due to large quantity chemical terms. I will only add that using colloidal synthesis it is possible to obtain nanocrystals coated with a layer of adsorbed surfactant molecules. Thus, they are soluble in organic solvents and, after modification, also in polar solvents.

Quantum dot design
Typically, a quantum dot is a semiconductor crystal in which quantum effects are realized. An electron in such a crystal feels like it is in a three-dimensional potential well and has many stationary energy levels. Accordingly, when moving from one level to another, a quantum dot can emit a photon. With all this, the transitions are easy to control by changing the dimensions of the crystal. It is also possible to transfer an electron to a high energy level and receive radiation from the transition between lower-lying levels and, as a result, we obtain luminescence. Actually, it was the observation of this phenomenon that served as the first observation of quantum dots.

Now about the displays
The history of full-fledged displays began in February 2011, when Samsung Electronics presented the development of a full-color display based on QLED quantum dots. It was a 4-inch display controlled by an active matrix, i.e. Each color quantum dot pixel can be turned on and off by a thin film transistor.

To create a prototype, a layer of quantum dot solution is applied to a silicon circuit board and a solvent is sprayed on. Then a rubber stamp with a comb surface is pressed into the layer of quantum dots, separated and stamped onto glass or flexible plastic. This is how stripes of quantum dots are applied to a substrate. In color displays, each pixel contains a red, green or blue subpixel. Accordingly, these colors are used with different intensities to obtain as many shades as possible.

The next step in development was the publication of an article by scientists from the Indian Institute of Science in Bangalore. Where were quantum dots described that not only luminesce? orange, but also in the range from dark green to red.

Why is LCD worse?
The main difference between a QLED display and an LCD is that the latter can cover only 20-30% of the color range. Also, in QLED TVs there is no need to use a layer with light filters, since the crystals, when voltage is applied to them, always emit light with a clearly defined wavelength and, as a result, with the same color value.

Liquid crystal displays consist of 5 layers: the source is White light, emitted by LEDs, which passes through several polarizing filters. Filters located at the front and rear, together with liquid crystals, control the passing light flux, reducing or increasing its brightness. This happens thanks to pixel transistors, which affect the amount of light passing through the filters (red, green, blue).

The generated color of these three subpixels, on which filters are applied, gives a certain color value of the pixel. The color mixing happens quite smoothly, but it is simply impossible to get pure red, green or blue this way. The stumbling block is filters that transmit not just one wave of a certain length, but a whole series of waves of different lengths. For example, orange light also passes through a red filter.

It is worth noting that the scope of application of quantum dots is not limited only to LED monitors; among other things, they can be used in field effect transistors, photocells, laser diodes, the possibility of using them in medicine and quantum computing is also being studied.

An LED emits light when voltage is applied to it. Due to this, electrons (e) are transferred from the N-type material to the P-type material. N-type material contains atoms with an excess number of electrons. P-type material contains atoms that lack electrons. When excess electrons enter the latter, they release energy in the form of light. In a conventional semiconductor crystal, this is typically white light produced by many different wavelengths. The reason for this is that electrons can be in different energy levels. As a result, the resulting photons (P) have different energies, which results in different wavelengths of radiation.

Light stabilization with quantum dots
QLED TVs use quantum dots as a light source - these are crystals only a few nanometers in size. In this case, there is no need for a layer with light filters, since when voltage is applied to them, the crystals always emit light with a clearly defined wavelength, and therefore color value. This effect is achieved by the tiny size of a quantum dot, in which an electron, like in an atom, is able to move only in a limited space. As in an atom, the electron of a quantum dot can only occupy strictly defined energy levels. Due to the fact that these energy levels also depend on the material, it becomes possible to specifically tune the optical properties of quantum dots. For example, to obtain red color, crystals from an alloy of cadmium, zinc and selenium (CdZnSe), the size of which is about 10-12 nm, are used. Cadmium and selenium alloy suitable for yellow, green and blue colors, the latter can also be obtained using nanocrystals from a compound of zinc and sulfur with a size of 2-3 nm.

Mass production of blue crystals is very difficult and expensive, so the TV introduced by Sony in 2013 is not a “thoroughbred” QLED TV based on quantum dots. At the back of the displays they produce is a layer of blue LEDs, the light of which passes through a layer of red and green nanocrystals. As a result, they essentially replace the currently common light filters. Thanks to this, the color gamut increases by 50% compared to conventional LCD TVs, but does not reach the level of a “pure” QLED screen. The latter, in addition to a wider color gamut, have another advantage: they save energy, since there is no need for a layer with light filters. Thanks to this, the front part of the screen in QLED TVs also receives more light than in regular TVs, which transmit only about 5% of the light flux.

Scientists have developed a theory for the formation of a widespread class of quantum dots, which are obtained from compounds containing cadmium and selenium. For 30 years, developments in this area have relied heavily on trial and error. The article was published in the journal Nature Communications.

Quantum dots are nano-sized crystalline semiconductors with remarkable optical and electronic properties that have already found applications in many fields of research and technology. They have properties intermediate between bulk semiconductors and individual molecules. However, unclear aspects remain in the process of synthesizing these nanoparticles, since scientists have not been able to fully understand how the reagents, some of which are highly toxic, interact.

Todd Krauss and Lee Frenette of the University of Rochester are looking to change that. In particular, they found that during the synthesis reaction toxic compounds appear, which were used to obtain the first quantum dots 30 years ago. “We essentially went 'back to the future' with our discovery,” explains Krauss. “It turned out that the safer reagents used today turn into precisely the very substances whose use they have been trying to avoid for decades. They, in turn, react to form quantum dots.”

First, it will reduce the guesswork involved in producing cadmium- or selenium-based quantum dots, which has led to inconsistencies and irreproducibility that have hampered the search for industrial applications.
Second, it will alert researchers and companies working with large-scale quantum dot synthesis that they are still dealing with such hazardous substances, like hydrogen selenide and alkyl-cadmium complexes, although not explicitly.
Third, it will clarify the chemical properties of phosphines used in many high-temperature quantum dot synthesis processes.

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