Synthesis, luminescence properties and nephelauxetic effect of nano stick phosphors K₃AlF₆:Mn⁴⁺ for warm white LED

The high uniformity of the phosphors may help to improve their luminescent properties, emission intensities and quantum efficiencies. In order to achieve this goal, a series of nano stick K₃AlF₆:xMn⁴⁺ samples with regular morphology are prepared in this paper. These samples show high photoluminescence quantum yields. Nano stick sample is obtained after recrystallization with vapor diffusion method. Furthermore, color purity, analyses of crystal-field and nephelauxetic effect, the critical distance and the related type of multipolar interaction for the samples were also discussed. The calculation results show that the Mn⁴⁺ ions are located at a site of a strong crystal field, and the concentration quenching of Mn⁴⁺ in the samples K₃AlF₆:xMn⁴⁺ may be dominated by dipole-quadrupole interactions. Decay lifetime and the photoluminescence QY (quantum yield) of the optimal nano stick sample are 2.50 ms and 89.34%, respectively. The chromaticity coordinates of the optimal nano stick sample are x = 0.6872 and y = 0.3126, which are very close to the NTSC (the national television systems committee) standard values for red color (x = 0.67, y = 0.33). Employing the as-prepared nano stick K₃AlF₆:xMn⁴⁺ as a red component, a high-performance WLEDs with a lower correlated color temperature (CCT = 4170 K) and a high color rendering index (CRI = 85.6) was obtained. It suggests the as-prepared K₃AlF₆:xMn⁴⁺ is a potential commercial red component for warm WLEDs.