Thermal Effects in Up-Conversion Luminescence NaYF: Tm, Yb Core-Shell Nanoparticles in the Temperature Range of 18-312 K.

This work demonstrates the temperature (18-312 K) impact on Tm up-conversion luminescence in core-shell structured NaYF:Tm, Yb nanoparticles excited at 976 nm. As the temperature decreases from room temperature to 18 K, Tm up-conversion luminescence bands intensities greatly increase, an average of 60-fold, emitting intense blue and ultraviolet radiation. Tm up-conversion luminescence spectra measurements at different temperatures reveal that three thermal quenching mechanisms are responsible for observed variations in Tm up-conversion luminescence spectra. These three quenching mechanisms are related to the excitation radiation absorption, Stark sublevel population, and energy transfer from Yb to Tm.