Presently, liquid crystal displays (LCDs) and organic light-emitting diode (OLED) displays are two dominant flat panel display technologies Recently, inorganic mini-LEDs (mLEDs) and micro-LEDs (μLEDs) have emerged by significantly enhancing the dynamic range of LCDs or as sunlight readable emissive displays "mLED, OLED, or μLED: who wins?" is a heated debatable question In this review, we conduct a comprehensive analysis on the material properties, device structures, and performance of mLED/μLED/OLED emissive displays and mLED backlit LCDs We evaluate the power consumption and ambient contrast ratio of each display in depth and systematically compare the motion picture response time, dynamic range, and adaptability to flexible/transparent displays The pros and cons of mLED, OLED, and μLED displays are analysed, and their future perspectives are discussed

/pdf/mini-led-micro-led-and-oled-displays-present-status-and-1231h0pbyk.pdf

Mini-LED, Micro-LED and OLED displays: present status and future perspectives

Micro-light-emitting diodes (μ-LEDs) are regarded as the cornerstone of next-generation display technology to meet the personalised demands of advanced applications, such as mobile phones, wearable watches, virtual/augmented reality, micro-projectors and ultrahigh-definition TVs. However, as the LED chip size shrinks to below 20 μm, conventional phosphor colour conversion cannot present sufficient luminance and yield to support high-resolution displays due to the low absorption cross-section. The emergence of quantum dot (QD) materials is expected to fill this gap due to their remarkable photoluminescence, narrow bandwidth emission, colour tuneability, high quantum yield and nanoscale size, providing a powerful full-colour solution for μ-LED displays. Here, we comprehensively review the latest progress concerning the implementation of μ-LEDs and QDs in display technology, including μ-LED design and fabrication, large-scale μ-LED transfer and QD full-colour strategy. Outlooks on QD stability, patterning and deposition and challenges of μ-LED displays are also provided. Finally, we discuss the advanced applications of QD-based μ-LED displays, showing the bright future of this technology. Micrometre-sized light-emitting diodes (LEDs) based on quantum dots (QDs) will propel the next generation of display technologies, a review by leading researchers shows. Conventional LED designs, with phosphor coatings that convert light to different colours, are difficult to make smaller than 20 micrometres. Jr-Hau He at City University of Hong Kong and co-workers explain how this problem can be tackled using QDs, tiny particles whose optical properties can be tuned by varying their size, providing brighter and more precise colours. Ultra-high-resolution displays based on phospholuminescent QD-LEDs are now being released to the market thanks to finely-controlled methods for synthesising QDs and depositing them onto films. Further research should focus on the best ways to stabilise and protect QD films within LEDs, and to continue developing electroluminescent QD-LEDs, which could potentially outperform their phospholuminescent cousins.

/pdf/micro-light-emitting-diodes-with-quantum-dots-in-display-539mmezpm0.pdf

Micro-light-emitting diodes with quantum dots in display technology

2-μm lasers with fluoride crystals: Research and development

Growth, transfer printing and colour conversion techniques towards full-colour micro-LED display

J Soc Inf Display. 2019;27:387–401. Abstract We review the emerging mini/micro–light‐emitting diode (LED) displays featuring high dynamic range and good sunlight readability. For mini‐LED backlit liquid crystal displays (LCDs), we quantitatively evaluate how the device contrast ratio, local dimming zone number, and local light profile affect the image quality. For the emissive mini/micro‐LED displays, the challenges of ambient contrast ratio and size‐dependent power efficiency are analyzed. Two figure‐of‐merits are proposed for optimizing the optical and electrical performances of mini/micro‐LED displays.

Prospects and challenges of mini-LED and micro-LED displays

Displays based on inorganic light-emitting diodes (LED) are considered as the most promising one among the display technologies for the next-generation The chip for LED display bears similar features to those currently in use for general lighting, but it size is shrunk to below 200 microns Thus, the advantages of high efficiency and long life span of conventional LED chips are inherited by miniaturized ones As the size gets smaller, the resolution enhances, but at the expense of elevating the complexity of fabrication In this review, we introduce two sorts of inorganic LED displays, namely relatively large and small varieties The mini-LEDs with chip sizes ranging from 100 to 200 μm have already been commercialized for backlight sources in consumer electronics applications The realized local diming can greatly improve the contrast ratio at relatively low energy consumptions The micro-LEDs with chip size less than 100 μm, still remain in the laboratory The full-color solution, one of the key technologies along with its three main components, red, green, and blue chips, as well color conversion, and optical lens synthesis, are introduced in detail Moreover, this review provides an account for contemporary technologies as well as a clear view of inorganic and miniaturized LED displays for the display community

Mini-LED and Micro-LED: Promising Candidates for the Next Generation Display Technology

Detailed polarized spectral properties of Tm3+:NaLa(MoO4)2 crystal have been investigated. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves were measured at room temperature. The fluorescence decay mechanisms of the G14 and H34 multiplets were discussed. Spectroscopic parameters related to the laser operation at around 1.9 μm via the F34→H36 transition have been evaluated. Room-temperature quasi-cw 1.9 μm laser emission from a Ti:sapphire laser pumped Tm3+:NaLa(MoO4)2 crystal has been demonstrated. The maximum output power of 0.5 W has been achieved with a slope efficiency of 50%.

Spectroscopic properties and laser performance of Tm3+-doped NaLa(MoO4)2 crystal

The metal halide perovskite nanocrystal (MHP-NC), an easy-to-fabricate and low cost fluorescent material, is recognized to be among the promising candidates of the color conversion material in the micro light-emitting diode (micro-LED) display, providing that the stability can be further enhanced. It is found that the water steam, oxygen, thermal radiation and light irradiation—four typical external factors in the ambient environment related to micro-LED display—can gradually alter and destroy the crystal lattice. Despite the similar phenomena of photoluminescence quenching, the respective encroaching processes related to these four factors are found to be different from one another. The encroaching mechanisms are collected and introduced in separate categories with respect to each external factor. Thereafter, a combined effect of these four factors in an environment mimicking real working conditions of micro-LED display are also introduced. Finally, recent progress on the full-color application of MHP-NC is also reviewed in brief.

https://www.mdpi.com/2079-4991/10/7/1375/pdf

The Stability of Metal Halide Perovskite Nanocrystals-A Key Issue for the Application on Quantum-Dot-Based Micro Light-Emitting Diodes Display.

Color gamut is of the paramount importance in the display. Light–current–voltage ( $L-I-V$ ) characteristics of red, green, and blue flip-chip mini-light-emitting diodes (LEDs) ( $100\,\,\mu \text{m}\,\,\times 200\,\,\mu \text{m}$ ) are investigated at temperatures similar to the operational temperatures. Both the ideality factor and the temperature dependence of external quantum efficiency (EQE) suggest that the nonradiative loss in red mini-LED is higher. We also illustrate the intensive lateral luminous intensity fluctuation for red mini-LED under the over-driving current by capturing the spatial emission mapping. The influence of temperature and driving current on the chromaticity coordinates of mini-LEDs is determined. Furthermore, we propose a drive-current algorithm to maximize the color gamut of the trichromatic mixed light at different temperatures. The results indicate that, for the application of self-emitting mini-LED displays, the maximum color gamut is more sensitive to green emission, whereas enhancing the radiative recombination in red mini-LED could contribute a lot to the improvement on net performance.

The Impact of Luminous Properties of Red, Green, and Blue Mini-LEDs on the Color Gamut

Lead–halide perovskite nanocrystals (PeNCs), especially those composed of iodine, suffer from degradation problems. Water vapor, oxygen, light, and heat can damage PeNCs and consequently quench their photoluminescence (PL). Thus, robust encapsulation against all these stresses is urgently required. In this study, inorganic encapsulation of mesoporous SiO2, in conjunction with a high-temperature sintering synthesis process under an inert atmosphere, is introduced. This synthesis process is compatible with various halide contents, yielding PeNCs sealed in SiO2 particles that emit PL emission covering the entire visible range from 420 to 700 nm. The PeNCs–SiO2 sample showed remarkable stability after undergoing aging tests under various exaggerated stresses as well as mitigated thermal quenching during thermal cycling. The color gamut constituted by three PeNCs–SiO2 samples approached 135.36% NTSC and 101.07% Rec. 2020, with remarkable chromatic stability. The PeNCs–SiO2 can be blended into a photoresist and remains luminous during the development procedure, which is compatible with the photolithography process; this facilitates the mass production of color conversion layers. All these advantageous features show that the material proposed herein has great potential for application in full-color displays such as micro and mini light-emitting diode displays.

Weijie Guo

Papers

Mini-LED and Micro-LED: Promising Candidates for the Next Generation Display Technology

Spectroscopic properties and laser performance of Tm3+-doped NaLa(MoO4)2 crystal

The Stability of Metal Halide Perovskite Nanocrystals-A Key Issue for the Application on Quantum-Dot-Based Micro Light-Emitting Diodes Display.

The Impact of Luminous Properties of Red, Green, and Blue Mini-LEDs on the Color Gamut

All-inorganic encapsulation for remarkably stable cesium lead halide perovskite nanocrystals: toward full-color display applications