Construction of thermally stable Tb3+-activated green-emitting phosphors: dual driving strategy of doping concentration and excitation wavelength.

ABSTRACT

The realization of thermally stable Tb3+-doped green emission at high temperatures in solid-state lighting is still a crucial challenge. Nevertheless, the study on modulating the thermally stable luminescence at high temperatures is seldom reported. The position of the intervalence charge transfer (IVCT) energy level is used to systematically investigate the thermal quenching performance of Tb3+-activated green-emitting phosphors with varying concentration gradients of Gd1-xTaO4xTb3+ (x = 0.1%, 0.5%, and 2%) in this study. The IVCT energy levels were determined according to the empirical formula to show a decreasing trend, consistent with the position of the IVCT energy levels measured in the excitation and diffuse reflectance spectra. Moreover, the thermal quenching performance of different wavelength excitation positions (host absorption, 4f-5d of Tb3+, and Tb3+-Ta5+ IVCT band) is quite different. The modulation of thermal quenching performance among distinct phosphors when subjected to host excitation or IVCT excitation can be elucidated through optimal positions within the energy levels associated with IVCT. The diverse concentration gradient samples exhibit varying degrees of thermal quenching performance in the variable-temperature spectra. The fluorescence lifetimes of the samples are generally comparable but slightly lower. The quantum efficiency rapidly improves as the Tb concentration increases. The underlying mechanism governing this phenomenon is elucidated by constructing a model that encapsulates the interplay between the compensating and quenching channels, in addition to the energy conversion of Tb3+ into Gd3+. The abovementioned results indicate that the dual driving scheme of the doping concentration and excitation wavelength is an effective means to regulate the thermal quenching performance of Tb-activated green-emitting tantalate phosphors.