A common full-color method involves combining micro-light-emitting diodes (LEDs) chips with color conversion materials such as quantum dots (QDs) to achieve full color. However, during color conversion between micro-LEDs and QDs, QDs cannot completely absorb incident wavelengths cause the emission wavelengths that including incident wavelengths and converted wavelength through QDs, which compromises color purity. The present paper proposes the use of a recycling-reflection color-purity-enhancement film (RCPEF) to reflect the incident wavelength multiple times and, consequently, prevent wavelength mixing after QDs conversion. This RCPEF only allows the light of a specific wavelength to pass through it, exciting blue light is reflected back to the red and green QDs layer. The prototype experiment indicated that with an excitation light source wavelength of 445.5 nm, the use of green QDs and RCPEFs increased color purity from 77.2% to 97.49% and light conversion efficiency by 1.97 times and the use of red QDs and RCPEFs increased color purity to 94.68% and light conversion efficiency by 1.46 times. Thus, high efficiency and color purity were achieved for micro-LEDs displays. Graphical Abstract

This study proposes a novel direct-lit mini-chip-scale packaged light-emitting diode (mini-CSPLED) backlight unit (BLU) that used quantum dot (QD) film, diffusion plate, and two prism films to improve brightness uniformity. Three different luminous intensity units, 120°mini-CSPLED, 150°mini-CSPLED, and 180°mini-CSPLED with different emission angle structures were fabricated using a CSP process. In terms of component characteristics, although the 180°mini-CSPLED light output power is about loss 4% (at 10 mA) compared with 150°mini-CSPLED, it has a large emission angle that forms a planar light source that contributes to improving the BLU brightness uniformity and reduced quantity of LEDs at the same area. In terms of BLU analysis, the blue mini-CSPLEDs with different emission angles excite the different QD film thicknesses; the chromaticity coordinates conversion to the white light region. The BLU brightness increases as the QD film thickness increases from 60, 90, and 150 μm. This result can achieve a brightness uniformity of 86% in a 180°mini-CSPLED BLU + 150-μm-thick QD films as compared to the 120°mini-CSPLED BLU and 150°mini-CSPLED BLU.

Displays composed of micro-light-emitting diodes (micro-LEDs) are regarded as promising next-generation self-luminous screens and have advantages such as high contrast, high brightness, and high color purity. The luminescence of such a display is similar to that of a Lambertian light source. However, owing to reduction in the light source area, traditional secondary optical lenses are not suitable for adjusting the light field types of micro-LEDs and cause problems that limit the application areas. This study presents the primary optical designs of dielectric and metal films to form highly reflective thin-film coatings with low absorption on the light-emitting surfaces of micro-LEDs to optimize light distribution and achieve full-angle utilization. Based on experimental results with the prototype, that have kept low voltage variation rates, low optical losses characteristics, and obtain the full width at half maximum (FWHM) of the light distribution is enhanced to 165° and while the center intensity is reduced to 63% of the original value. Hence, a full-angle micro-LEDs with a highly reflective thin-film coating are realized in this work. Full-angle micro-LEDs offer advantages when applied to commercial advertising displays or plane light source modules that require wide viewing angles.

The field of next‐generation microdisplays is flourishing. Relevant display technologies, such as mini‐light emission diodes (mini‐LEDs), micro‐organic light emission diodes (micro‐OLEDs), and micro‐light emission diodes (micro‐LEDs) are thus in the urgent stage of development. From this perspective, comprehensive and systematical analyzes are conducted for the aforesaid microdisplay configurations. A holistic view of microdisplay technologies is developed with the corresponding performance metrics, providing a path for miscellaneous scenarios. Among these scenarios, the applications in augmented reality (AR), virtual reality (VR), wearable devices, and head‐up displays (HUD) are currently attracting considerable attention for deeper human‐digital interactions. However, there is a multiplicity of obstacles and challenges hindering such development. Nevertheless, recent advances in microdisplay technologies hold tremendous promise for the paradigms of these applications, taking a leap forward for next‐generation microdisplays. This review presents perspectives, relevant materials, and the technology landscape for such ongoing display technologies, offering guidance on the design of advanced microdisplays.

The demand for extra-thin, large-area, and high-luminance flat-panel displays continues to grow, especially for portable displays such as gaming laptops and automotive displays. In this paper, we propose a design that includes a light guide layer with a microstructure above the mini-light-emitting diode light board. The light control microstructure of concave parabel-surface microlens arrays on a light-emitting surface increases the likelihood of total internal reflection occurring and improved the uniformity merit function. We used a 17 in prototype with quantum-dot and optical films to conduct our experiments, which revealed that the thickness of the module was only 1.98 mm. When the input power was 28.34 watts, the uniformity, average luminance, and CIE 1931 color space NTSC of the prototype reached 85%, 17,574 cd/m2, and 105.37%, respectively. This module provided a flat light source that was extra thin and had high luminance and uniformity.

Traditional backlights are designed with new dot patterns, and then injection molding, laser beam fabrication, or UV (Ultraviolet) roll-to-plate imprinting is used to apply dot patterns to a light guide plate—the process consumes considerable time and resources. Therefore, we propose a novel light guide design that does not use a dot pattern. We designed an asymmetric intensity distribution of mini-LEDs (Light Emitting Diode) and a light guide plate with a fully printed diffusion reflection on the bottom surface for a planar illuminator. The design rules for the proposed architecture are described in this paper. The archetype design with a 152.4 mm circular down-light has a diameter of 143 mm for the planar light source module. The experiment achieved a total efficiency of 85% and uniformity of 92.6%.

Light-emitting diodes (LEDs) have numerous advantages. However, LEDs only offer a point light source. Therefore, transforming LEDs into planar light sources is a new objective in general lighting applications. Solid light guides have strong uniformity but are marred by their material absorption characteristics and weight. Hollow light guides constitute a solution to the weight problem but exhibit poor uniformity and necessitate sacrificing efficiency to enhance uniformity. To resolve the uniformity, weight, and efficiency problems simultaneously, we propose a hollow light guide architecture involving mini-LEDs with asymmetric luminous intensity. To develop this guide module, we first optimized the aspect ratio of the cavity and then modulated the light path by using varied angles of the reflection surface on the end wall of the module. We then designed a beveled reflection surface near the mini-LEDs to further enhance uniformity. An archetype of the proposed architecture for planar light source modules had a width and depth of 51.5 and 9.95 mm, respectively. Experimental results revealed a total efficiency of 83.9% and uniformity of 92.3%. The module weight was determined to be 215 g, which was 40% lighter than that of similarly sized solid light guide modules.

To realize high-efficiency AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs), enhancing their light-extraction efficiency (LEE) is crucial. This paper proposes an aluminum-based sidewall reflector structure that could replace the conventional ceramic-based packaging method. We design optimization simulations and experimental results demonstrated the light power output could be enhanced 18.38% of DUV-LEDs packaged with the aluminum-based sidewall.