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Discovery of highly efficient and thermal stable phosphors is a major topic in phosphor-converted white light-emitting diodes (LEDs). A highly efficient and zero-thermal quenching blue-emitting phosphor is realized in nominal Km-0.4Al11O17+δ:0.2Eu2+, which benefits from rigid aluminate structure with space group P63/mmc and the introduction of trap energy levels. The internal and external quantum efficiencies of optimal nominal K1.6Al11O17+δ:0.2Eu2+ are 97.1% and 61.8%, respectively. The phosphor exhibits zero-thermal-quenching behavior within 150 °C. Further increasing K content results in even better thermal stability, however, lower quantum efficiency. The relationship between luminescence properties and crystal structure was discussed. Results suggest that the blue-emitting phosphor is a candidate for white phosphor-converted LEDs based on near-UV or violet chip.

A series of ZnS:KBr,x%Mn2+ (x = 0–0.25) phosphors with dynamic multicolor luminescence are obtained by simultaneously constructing strong host luminescence and heterochromatic doping emissive center in ZnS lattice. Under a fixed ultraviolet irradiation, the phosphors emit tunable colors ranging from cyan to yellow-orange with increasing x values gradually. Besides, those Mn2+-doped phosphor (x > 0) emits different colors under different UV excitations. After removal of the UV lamp, all ZnS:KBr,Mn2+ phosphors exhibit an orange afterglow that is different from its photoluminescence (PL) color. The dynamic PL and afterglow is associated with the interactions between two PL centers and traps in the material. Therefore, spatially and temporally resolved dynamic multicolor luminescence is realized by tuning doping concentration, excitation wavelength, and observation time, which features the ZnS:KBr,Mn2+ phosphors a great application potential in high-level secure anti-counterfeiting.

Poor humidity resistance is a bottleneck problem to be solved urgently for Mn4+ activated fluoride red phosphors. At present, some strategies such as outer coating, cation exchange (CE), and surface passivation (SP) have been developed, but the effect is limited. The key reason is that the easily hydrolyzed Mn4+ ions on the surface are difficult to be completely removed. With the goal of achieving a significant improvement in the moisture resistance of fluoride, this work proposes a new idea of using the reduction-assisted surface recrystallization (RSRC) strategy to construct a real core-shell structure without Mn4+ in the shell. The quantum efficiency (QE) of the K2SiF6:Mn4+ treated by the RSRC method is 99.95%. After boiling in water, the QE can even be maintained at 96.7%, which is significantly higher than that of the fluorides treated by CE (15.53%) or SP (62.64%) methods. The Mn-free shell is further determined by a combination of in-situ lift-out and STEM-EDX techniques. Finally, the aging results of LED devices in high temperature (85 °C) and high humidity (85%) environments further confirmed that the color stability of the K2SiF6:Mn4+ was significantly improved.

Thermally stable phosphors are crucial for the application in phosphor-converted white light-emitting diodes. This paper reports the evolution of phase compositions in nominal Na2−xAl2B2O7:xEu (x = 0.02–2.0) upon replacing Na atoms by Eu atoms. Eu2+-activated blue-emitting phosphor was discovered through phase segregation combined with related analyses. The structure, phase composition and related luminescent properties were investigated by X-ray powder diffraction, backscattered electron image combined with elemental mapping, cathodoluminescence-combined scanning electron microscope, and temperature-dependent emission spectra, etc. Analyses results suggest that EuBO3 phase segregates upon the gradual replacement of Na by Eu atoms, which is accompanied by phase transformation from Na2Al2B2O7:Eu2+ to NaAl11O17:Eu2+ and dramatic enhancement of blue emission. The broad emission band is peaking at around 470 nm under UV irradiation. The internal quantum efficiencies of nominal Na0.4Al2B2O7:1.6Eu and Na0.2Al2B2O7:1.8Eu are 58.6% and 60.2%, respectively, which contain both NaAl11O17 and EuBO3 phase. The emission intensity for these two samples at 150 °C remains 96% (x = 1.6) and 83% (x = 1.8) of the room-temperature values, respectively.