Large negative thermal quenching of upconversion luminescence through selective excitation in a YAG:Yb/Er transparent ceramics

Abstract

This study has demonstrated a salient negative thermal quenching behavior of upconversion (UC) luminescence in YAG:Yb/Er transparent ceramic phosphor in a wide temperature range from 100 to 500 K. With the rise of temperature, UC luminescence deteriorates under the excitation at λex = 932 nm, whereas it intensifies remarkably at λex = 974 nm (i.e., the integrated emission intensity increased by nearly 30 folds from T = 100 K to T = 500 K), indicating a dynamic UC luminescence-temperature relation dependent upon the incident excitation energy. Our later photophysical analysis shows that the negative thermal quenching behavior was mainly ascribed to a phonon-assisted thermal excitation process which occurs at low excitation energy. More interestingly, it is found that despite a final decline at high temperature, the UC luminescence lifetime increases as the temperature rises before certain degrees. A modified equation for luminescence lifetime was proposed and used for our interpretation. This work not only demonstrates large negative thermal quenching of UC luminescence in the ceramic phosphor for the first time, but also provides a deep insight into the photophysical behavior of UC luminescence.