Temperature dependence of fluorescence dynamic behavior of wide-bandgap compounds

In this work, the transition properties of wide-bandgap compounds are studied by way of the temperature dependence of fluorescence dynamic curves. The YVO₄, CaWO₄, and CaMoO₄ samples are selected in this study owing to their strong absorption in the ultraviolet (UV) region. The fluorescence decay curves of the three samples, in the range of 173–373 K, are measured under excitation by deep UV light-emitting diodes (LEDs). The temperature dependence of transition rate (A) is composed of a constant term, as well as a mono-exponential term which follows the Boltzmann distribution law. The constant term reflects a spontaneous radiative transition rate (W_R), while the mono-exponential term represents the temperature-dependent nonradiative transition rate (W_NR). The nonradiative relaxation is attributed to the upward thermal population rather than the downward multiphonon relaxation (MPR). The thermal populating process is supposed to originate from the bottom of the excited state to the intersection of the ground state and excited state by overcoming the potential barrier of activation energy (E_a), and the E_a values of YVO₄, CaWO₄, and CaMoO₄ samples are calculated.