Quantum dots. Quantum dots - a new technology for producing displays

« Quantum dots- these 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 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 spectators are excited electronic levels having 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 most best places- 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're probably wondering what happens to that empty space at 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 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 inclusions of structures of one type of semiconductor material 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 who dream of " quantum computers“, see quantum dots as promising candidates for constructing 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.

Many new display technologies are being demonstrated at international exhibitions, but not all of them are viable or have the appropriate capabilities for successful commercial implementation. One of the pleasant exceptions is quantum dot technology, which is already used in the backlight of LCD displays. It is worth talking about this technical innovation in more detail.

Quantum dots

Quantum dots are nanoparticles semiconductor materials. Their parameters are determined by their size: as the size of the crystal decreases, the distance between the energy levels increases. When an electron moves to a lower level, a photon is emitted. By changing the size of the dot, you can adjust the photon energy and, as a result, the color of the light.

This is not a new discovery; in fact, quantum dots were created more than thirty years ago. But until recently they were used only in special scientific instruments in laboratories. Strictly speaking, quantum dots are microscopic elements capable of emitting light in a narrow wavelength range. Moreover, depending on their size, the light can be green, red or blue.

By changing their size, you can finely control the wavelength of the emitted light. This technology, used in modern models televisions, dates back to 2004, when the QD Vision company was organized. Initially, the employees of this research laboratory tried to use quantum dots to replace organic dyes when labeling various biological systems, but then they decided to try the technology on televisions.

Well-known companies soon joined this idea. In particular, in 2010, researchers worked together with LG on the QLED project. However, the very concept of technology in relation to LCD TVs was constantly subject to changes, its working name also changed several times. A year later, in collaboration with Samsung, a prototype of a color screen based on quantum dots was created. However, he did not go into series. The latest implementation of this concept is part of Sony's Color IQ technology, which introduced the Triluminos backlit screen.

As you know, all LCD TVs create a picture by mixing basic colors - red, green and blue (RGB model). Sometimes yellow is added, which, however, does not significantly affect the system of creating pictures on the LCD screen. Mixing RGB colors in LCD TVs it is carried out using color filters, and in plasma panels – thanks to a phosphor.

In classic LCD models, “white” LEDs are used as backlight. The color in the white spectrum, passing through color filters, gives a certain shade. More advanced models use phosphor LEDs that emit light in the blue region. This light then mixes with yellow to become visually white. To create the same on the screen from a similar white, respectively, red, blue and green filters are used. This is quite effective, but still wastes a lot of energy. In addition, here engineers have to look for a certain balance between color rendering quality and backlight brightness.

Advantages of quantum dot TVs

Two years ago, Sony first introduced mass-produced models of television devices with Triluminos backlighting, which uses quantum dots. This is, in particular, the KD-65X9000A. The backlight uses blue diodes, but there is no yellow phosphor. As a result, blue light, without mixing, directly passes through a special IQ element that contains red and green quantum dots. The manufacturer calls the main advantages of the technology deeper color rendition and minimization of losses in brightness.

It is expected that, in comparison with LED backlighting, quantum dots will provide an increase in color range almost 50 percent. The color gamut in the new Sony TVs with Triluminos backlighting is close to 100% NTSC, while models with regular backlighting have about 70% NTSC. Thus, it can be stated that quantum dot backlit TVs can indeed improve image quality, making color reproduction more realistic.

But how much more realistic? After all, it is known that in the same Sony TVs the picture is created using the usual filters that mix colors? It is quite difficult to answer this question; a lot depends on the subjective perception of image quality. In any case, the happy owners of the first Sony TVs with the new backlight note that the image on the screen looks like a painting painted with purer color paints.

The fact that other leading companies instantly joined in the implementation of this technological innovation, confirms the fact that quantum dots are not exclusively marketing ploy. At CES 2015, Samsung presented SUHD TVs, which also implemented similar technology. It is noted that new TVs provide more high quality images at a price lower than OLED models. LG also presented TVs with Quantum Dot technology at the ULTRA HD exhibition.

The comparison with OLED is not accidental. After all, many companies first turned to OLED technology as a way to improve image quality modern TVs, but encountered problems with their production when they were launched into series. This is especially true for OLED TVs with large screen diagonals and ultra-high resolution.

In the form of quantum dots, a kind of backup option was found - the color gamut on such TVs is almost as good as on OLED displays, and there are practically no problems with the industrial development of the technology. This allows companies to produce TVs that will rival OLED technology in picture quality, while remaining affordable to a wide range of consumers.

Quantum dots- these are tiny crystals, emitting light with precisely adjustable color value. Quantum dot LED technology significantly improves image quality without affecting final cost devices, in theory :).

Conventional LCD TVs can only cover 20-30% of the color range that the human eye can perceive. The image is not very realistic, but this technology is not focused on mass production of large display diagonals. Those who follow the TV market remember that back in early 2013 Sony introduced the first TV based on quantum dots (Quantum dot LED, QLED). Major TV manufacturers will release quantum dot TV models this year; Samsung has already presented them in Russia under the name SUHD, but more on that at the end of the article. Let's find out how displays produced using QLED technology differ from the already familiar LCD TVs.

LCD TVs lack pure colors

After all, 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 whole line different wavelengths. For example, orange light also passes through a red filter.

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

IN QLED TVs Quantum dots act 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 target the optical properties 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 zinc-sulfur compound with a size of 2–3 nm.

Mass production of blue crystals is very difficult and expensive, so introduced in 2013 by Sony TV is not "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 conventional TVs, which transmit only about 5% of the luminous flux.

QLED TV with Quantum Dot Display from Samsung

Samsung Electronics presented in Russia premium TVs made using quantum dot technology. New products with a resolution of 3840 × 2160 pixels were not cheap, and the flagship model was priced at 2 million rubles.

Innovations. Curved Samsung TVs SUHD on quantum dots differ from common LCD models by more high performance color rendering, contrast and power consumption. The integrated SUHD Remastering Engine allows you to upscale low-resolution video content to 4K. In addition, the new TVs received Peak Illuminator and Precision Black intelligent backlighting, Nano Crystal Color technology (improves color saturation and naturalness), UHD Dimming (provides optimal contrast) and Auto Depth Enhancer ( automatic setting contrast for certain areas of the picture). The software basis of televisions is operating system Tizen with the updated Samsung Smart TV platform.

Prices. The Samsung SUHD TV family is presented in three series (JS9500, JS9000 and JS8500), where the cost starts from 130 thousand rubles. This is how much the 48-inch model UE48JS8500TXRU will cost Russian buyers. The maximum price for a TV with quantum dots reaches 2 million rubles - for the UE88JS9500TXRU model with an 88-inch curved display.

New generation TVs using QLED technology are being prepared by South Korean Samsung Electronics and LG Electronics, Chinese TCL and Hisense, and Japanese Sony. The latter has already released LCD TVs made using quantum dot technology, which I mentioned in the description Quantum technologies dot LED.

The modern world is overflowing with all kinds of information. People are especially interested in the area medical discoveries. You can often hear about such a marvelous device as Pankov glasses. Reviews from many practitioners are quite encouraging, but there are also impressions that are not as rosy as the advertising of the device promises. What are miraculous glasses, and what is the essence of their use in the field of vision restoration for adults and children?

The method of influencing the eyes with Professor Pankov’s quantum glasses

The essence innovative methodology Pankov's eye treatment consists of restoring vision by exposing the retina to colored radiation. The structure of the human eye is such that it distinguishes colors according to the impulse of the brain to certain nerve endings. When the eyes are exposed to various color radiations at a rapid pace, all tissues and nerve endings are excited, blood supply improves and those areas that seem to no longer perform their function are revived.

The new device, used in many medical centers for vision restoration, has positive reviews. Pankov's glasses, according to many experts in the field of ophthalmology and color therapy, deserve the attention of those people who lose their vision or have side effects from working at the computer.

At its core, Pankov's quantum glasses are a training stimulator that improves the physiological purpose of each component of the eye apparatus. A lot of opinions today are focused on the topic of what Pankov’s quantum glasses are. Reviews can be both flattering and negative.

Where can I find detailed information about the Pankov device?

Before the device project was approved and allowed for mass production for the purpose of being used in the medical field to treat people’s vision, the author, Professor Pankov, wrote an interesting work on the topic of the possibility of restoring vision precisely by exposing the eyes to all shades of the rainbow.

What Pankov's glasses look like, reviews about this device can be found without any problems. But with conflicting information from different sellers, it is not always possible to specifically understand what this device actually treats and how to use it. Therefore, in most cases, those who really need help in restoring their vision turn for explanations to the professor’s book, which describes the physiological meaning of each color - “The Rainbow of Epiphany.” Pankov's glasses and reviews of them are directly related to the book.

Today's market medical devices is full of fakes, the instructions for the devices sold in almost every second case include descriptions from the author's source, but they are not entirely specific regarding their use in practice.

The book describes methods of influencing lighting, which is a warm-up. But exercises, such as watching fish in an aquarium with colored lighting, are not always effective. But the device created by the author - Professor Pankov's glasses - received well-deserved recognition due to the rhythm of its work. Reviews, of course, cannot give a detailed answer about the effectiveness of the device. To get a reliable assessment of glasses for vision restoration, you also need to know the opinion of professional ophthalmologists.

Without the prescription of an ophthalmologist, the device is not used in practice. The effect of it can only be assessed professionally by a specialist.

The effect of glasses on vision restoration

Pankov glasses affect the eyes in the following way:

• due to the supplied light signals, the eye muscles are massaged; the spasm of the pupil is relieved, which during training either narrows or expands;

• due to the rhythmic operation of the ocular apparatus, the outflow of intraocular fluid improves, and the anterior chamber of the eye receives fluctuations in the depth of image perception;

• muscle contraction improves blood circulation, due to which effective microcirculation occurs in the retina of the eye, nutrition of all tissues improves, and therefore visual perception improves.

In most cases, Pankov glasses deserve positive reviews when used as a simulator for the prevention of advanced eye diseases, as well as for training the vision of people professional sphere whose activities are associated with a large load on the eyesight: computer specialists, accountants, cashiers, researchers, pilots.

Pankov glasses are prescribed by an ophthalmologist for the initial degree of cataracts, asthenopia, amblyopia, progressive myopia, glaucoma, strabismus, myopia, developed farsightedness, and retinal dystrophy.

Based on positive reviews, Pankov glasses are also recommended for the prevention of complications in the postoperative period if surgery was performed in the eye area.

Factors that determine the use of glasses

• Analyzing all the reviews, Pankov glasses should be used as a simulator office workers, which have virtually no interruptions in their work while processing data on computer equipment.
• Students who have to strain their eyes while reading books both day and night also speak positively about the devices.
• Pankov's glasses are also useful for those who wear modern lenses instead of regular glasses, which cause their eyes to get tired and often turn red.
• In many situations, an ophthalmologist prescribes training with the device if he is sure of the threat of developing a particular eye disease.
• The use of the device is especially useful when a specialist diagnoses a spasm of accommodation.

Possible contraindications for using an innovative vision simulator

The use of the Pankov device is not permitted for severe inflammatory processes of the eyes, mental illness, oncology, diseases of the central nervous system, pregnancy, severe forms diabetes mellitus, pulmonary tuberculosis, recovery from a heart attack or stroke, and practice on children under three years of age is not recommended.

All the pros and cons of using a device to restore vision

As mentioned above, many who have encountered Pankov’s glasses in practice note a positive effect after undergoing a course of treatment under the supervision of an ophthalmologist. Number of patients childhood in general, it exceeds the number of patients in the middle and elderly age categories. Practice shows the importance of correction at an early age.

People who decide to use the device without a doctor’s prescription cannot evaluate the effect professionally, which is why many negative reviews who attribute this discovery to nothing more than quackery.

Advice from professional ophthalmologists regarding the use of Pankov glasses

Every ophthalmologist, before prescribing a course of treatment with Pankov glasses, always makes a clear diagnosis. The device may not provide positive changes in improving vision if the disease is too advanced. Pankov glasses can only be used after drug treatment, after relieving inflammation.

Where can I buy Pankov glasses?

What you definitely should not do, based on the above, is purchase the device through online stores. The reason for this is that there are a lot of counterfeits of effective medical devices and a lot of advertising.

Moreover, the advertising of the device focuses the buyer’s attention to a greater extent not on its training purpose, but on medicinal properties. Pankov's glasses are especially actively offered on the websites of megacities. So, as an example, we assessed the opinions of residents of St. Petersburg about this device, who bothered to purchase it through virtual sellers and test it in practice. If you study these reviews, Pankov’s glasses (St. Petersburg is not the only region whose residents fell for the tricks of advertisers) caused a lot of negative characteristics and mistrust of this innovation.

So you should restore your vision by visiting an ophthalmologist, and if you buy a device, then only on the recommendation of a competent doctor, who certainly won’t give bad advice.