Mn4+-Doped K2SiF6 (KSF:Mn4+) is identified as a promising down-conversion narrow-band red phosphor used in warm-white light emitting diodes (wLEDs) or wide color gamut LED backlights, owing to its outstanding photoluminescence properties. However, the highly toxic and concentrated HF is essentially used as a raw material to synthesize KSF:Mn4+ phosphors, which leads to environmental and safety issues. Herein, we report a novel green synthetic route to prepare highly efficient KSF:Mn4+ red phosphors using non-toxic NH4F/HCl instead of HF. The microstructure, photoluminescence properties and reaction mechanisms of the title phosphor were investigated and discussed. The KSF:Mn4+ phosphor (4.8% Mn) synthesized by this green route exhibits a spherical particle morphology and a fine particle size of 5.5 μm. The internal and external quantum efficiencies of the phosphor are 92 and 44% under 460 nm excitation, respectively. A warm wLED using KSF:Mn4+, YAG:Ce3+ and a blue LED chip is demonstrated to have a luminous efficacy of 137.2 lm W−1, a correlated color temperature of 3585 K and a color rendering index of Ra = 88.1, respectively. This indicates that the proposed green synthetic approach enables the preparation of highly efficient KSF:Mn4+ phosphors that have a comparable ability with the commercial ones to produce warm wLEDs.
A facile strategy to modify the surface of K 2 SiF 6 :Mn 4+ (KSFM) with commercially available hydrophilic hydroquinone (HQ) has been developed and waterproof stability (moisture resistance) of the KSFM has been significantly improved. It has been demonstrated that there are strong interactions between KSFM and HQ on the interface due to the hydrogen bonds of fluorine in KSFM with hydrogen in HQ. The relative luminous intensity of HQ-modified KSFM (denoted as KSFM-HQ) remained 99.7% of its initial value after immersion in water for 336 h, remarkable higher than that of KSFM which remained only 38.0%. It is proposed that the high water resistance of KSFM-HQ is achieved via two possible mechanisms: in situ decomposition of dark brown manganese (owing to the hydrolysis of [MnF 6 ] 2− ) on the KSFM crystal surface and consequently the formation of a more protective Mn 4+ -free layer. The process effectively combines the advantages of transparent organic materials (herein HQ) before immersion in water and durable moisture resistance of inorganic materials (herein K 2 SiF 6 ) on surface after immersion in water. The importance of HQ loading on moisture-sensitive fluoride phosphors has been further confirmed by using HQ-treated K 2 GeF 6 :Mn 4+ (KGFM) as an additional example. This strategy provides a one-of-a-kind way to the development of water-resistant Mn 4+ -doped fluoride phosphors with high luminous stability for potential applications in water-borne fluorescent anti-counterfeiting ink and even warm WLEDs operating in high humidity.
All-inorganic CsPbBr3 perovskite quantum dots (QDs) are considered to be one of the most promising green candidates for the new-generation backlight displays. The pending barriers to their applications, however, lie in their mismatching of the target window of green light, scalable production, susceptibility to the leaching of lead ions, and instability in harsh environments (such as moisture, light, and heat). Herein, high-quality CsPbBr3 QDs with globoid shapes and cuboid shapes were in situ crystallized/grown inside a well-designed glass to produce nanocomposites with peak emission at 526 nm, which not only exhibited photoluminescence quantum yields of 53 and 86% upon 455 and 365 nm excitation, respectively, but also have been imparted of high stability when they were submerged in water and exposed to heat and light. These characteristics, along with their lead self-sequestration capability and easy-to-scale preparation, can enable breakthrough applications for CsPbBr3 QDs in the field of wide color gamut backlit display. A high-performance backlight white LEDs was fabricated using the CsPbBr3 QDs@glass powder and K2SiF6:Mn4+ red phosphor, which shows a color gamut of ∼126% of the NTSC or 94% of the Rec. 2020 standards.
危险品化学品经营许可证（带存储）