Ultra-small Stokes shift induced thermal robust efficient blue-emitting alkaline phosphate phosphors for LWUV WLEDs

High power phosphor converted light emitting diodes (pc-LED) are thought to be the next generation technology for lighting and high-tech electronics applications. To achieve optimal luminous efficiency, maximal color gamut and stable color reproducibility, the discovery of high efficient phosphor materials with suitable excitation matching, narrow band emission and robust thermal stability is essential. Herein, we design and construct a new family of alkaline phosphate phosphors ANa(3)Mg(7)(PO4)(6):Eu2+ (ANMP:Eu2+, A = K, Rb and Cs) with rigid diamond-like chain structure. The results indicates that ANMP:Eu2+(A = K, Rb and Cs) phosphors exhibit ultra-small Stokes shift and efficient blue emission (lambda(max) = 444-465 nm) with high internal quantum efficiency (IQE = 83.2%, 90.6% and 93.4% for A = K, Rb and Cs), narrow full width at half maximum (FWHM similar to 50 nm) and low thermal quenching (87.5%, 96.5% and 84.2%@140 degrees C for A = K, Rb and Cs), which demonstrate to have higher colorful purity, wider color gamut and better wavelength applicability for using in long-wavelength near ultraviolet (LWUV) LEDs, compared with the traditional commercially available blue phosphor BaMgAl10O17:Eu2+ (BAM:Eu2+). The Eu2+ site preferences and thermal quenching mechanism are studied in detail. Moreover, the in situ temperature dependent Raman spectra and density function theory (DFT) are employed to get better comprehensions of the relationship between crystal-electronic structures and luminescent properties from experiment and calculation, which will provide a good guidance for develop new phosphors with high QE and excellent thermal stability. Finally, utilizing the title phosphors, white LED lamps are fabricated with high color rendering index and an appropriate correlated color temperature. Therefore, all the results demonstrate that the blue-emitting phosphor ANMP:Eu2+ (A = Cs, K, Rb) has great potential for applications in high power LWUV pumped pc-LEDs.