Single‐Crystal Red Phosphors: Enhanced Optical Efficiency and Improved Chemical Stability for wLEDs

Abstract

Crystal phosphors have many unique advantages compared with powdery ones. Herein, room‐temperature‐grown millimeter‐sized single‐crystal phosphors of Cs2XF6:Mn4+ (X = Ge, Si, and Ti) with remarkably higher external quantum efficiency than the corresponding powdery samples are reported. In addition, as compared with the powdery ones, the crystal samples exhibit much better stability toward water under different pH conditions. The red light‐emitting diodes (LEDs) based on Cs2XF6:Mn4+ crystals show significantly improved luminous efficiency than those based on their corresponding powders. An assembled white LED device composed of the two layers of phosphors, i.e., the crystal (such as Cs2GeF6:Mn4+) and commercial Y3Al5O12:Ce3+, on a blue chip exhibits intense warm white light with high luminous efficiency (up to 193 lm W−1), high color rendering indexes (88), and low correlated color temperatures (3107 K). Hence, these crystals with greatly improved efficiency and stability can be potentially applied in high‐quality LED backlighting display and white LED lighting, especially inside the micro‐LED devices.

Halide perovskites for light emission and artificial photosynthesis: Opportunities, challenges, and perspectives

“…Stable and efficient white‐light emission is necessary for lighting applications. Currently, the most used solid‐state lighting sources are the phosphor‐converted LEDs based on blue‐emitting chip, a class of mixed and multiple emitters 90,91 . Although this type of light source has the advantages of high efficiency and high brightness, its shortcomings are also obvious, such as the efficiency losses caused by self‐absorption, the instability of colors due to the different degradation rates of phosphors, the complex device structure and the use of rare earth elements, and so forth 92 .…”

Single‐Crystal Red Phosphors and Their Core–Shell Structure for Improved Water‐Resistance for Laser Diodes Applications

“…It is known that single crystals usually have more advantages over TC and PIG, and could be a good choice to increase transparency, improve efficiency, and maintain high waterproofness. Therefore, the performance of WLEDs packaged with crystals will certainly be enhanced, including energy conversion efficiency, stability, and lifetime [19] . There are many mature methods to grow high‐quality YAG:Ce 3+ single crystal [2] .…”

Three Birds with One Stone: K2SiF6:Mn4+ Single Crystal Phosphors for High‐Power and Laser‐Driven Lighting

“…[27] As shown in Figure S12a-c (Supporting Information), the EQE of KSFM (3d) crystal is as high as 78.2%, which is much higher than that of the KSFM-CP phosphor (67.5%). Moreover, the EQE of KSFM (3d) is higher than those of the previously reported Mn 4+ -doped fluoride phosphors, such as K 2 GeF 6 :Mn 4+ (73%), [10] K 3 AlF 6 :Mn 4+ (51%), [4d] Rb 2 GeF 6 :Mn 4+ (58%), [28] Cs 2 SiF 6 :Mn 4+ (71%), [8] K 2 TiF 6 :Mn 4+ (60.0%), [7a] and Cs 2 GeF 6 :Mn 4+ (66.9%) single crystals, [29] suggesting great potential during the commercial applications. It is also noted that the internal quantum efficiency (IQE) of the KSFM (3d) (90.4%) is lower than the commercial KSFM-CP (93.3%) due to the increasing of direct energy transfer to quenching sites (defects and impurity ions).…”

“…[30,31] A possible way is originated from the elemental impurities (OH − , O 2− , Mn 3+ , Mn 2+ ) defects causing quenching either by energy transfer or metalmetal charge transfer in typical K 2 SiF 6 :Mn 4+ phosphors, [32] and more backscattering and self-absorption of the KSFM-CP phosphor particles increase the nonradiative loss. [29] The photoluminescence decay curves at various temperatures are shown in Figure S13c,d (Supporting Information), and the temperature dependence lifetime can be seen in Figure 4d. It is found that the KSFM(3d) and the KSFM-CP basically have the same decay trend with elevated temperatures, indicating that the increase of doping concentration will not significantly affect the luminescence attenuation of Mn 4+ even at high temperature.…”