Luminescence Temperature Quenching in Mn2+ Phosphors

Abstract

Narrower band red and green emission in phosphor-converted white light-emitting diodes (wLEDs) can improve the efficacy and color gamut in lighting and display applications. A promising luminescent ion is Mn2+ that can have both narrowband green (tetrahedral coordination) and red (octahedral coordination) emission. Unlike in earlier lighting applications of Mn2+ phosphors, temperature quenching is important in wLEDs. Insight into the thermal quenching behavior of Mn2+ luminescence is lacking. Here systematic research is reported for a variety of Mn2+-doped phosphors; a huge variation in the luminescence quenching temperature T50, ranging from 50 K for Mn2+ in ZnTe to 1200 K in MgAl2O4, is revealed. The value T50 shows a positive correlation with the bandgap of the host, but no correlation with the full width half maximum (FWHM) of the emission band, indicating that thermally activated photoionization, not thermal crossover, is the operative quenching mechanism. This is confirmed by thermally stimulated luminescence (TSL) measurements that show a rise in TSL signal following photoexcitation at temperatures around T50 providing evidence that quenching is correlated with generation of free charge carriers. Based on these findings, as a design rule is obtained that for temperature-stable Mn2+ luminescence in (high power) LEDs a wide-bandgap host material is required.