A steady-state rate equation inversion method for quantitative measurement of temperature-dependent absorption in strongly absorbing oxysalts

A steady-state rate equation-based inversion method was proposed to quantitatively obtain temperature-dependent absorption spectra of strongly absorbing solids without requiring a transmission path. By jointly analyzing the photoluminescence, photoluminescence excitation, and time-resolved spectra of CaMoO₄ and CaWO₄, together with the Xe-lamp spectrum, the relative absorption cross sections (<i>σ</i>_rel) of MoO₄^2- and WO₄^2- groups were derived over 173-373 K. The integrated <i>σ</i>_rel of the MoO₄^2- groups increases nearly monotonically with temperature, in contrast to the thermal quenching behavior typically observed in conventional PLE spectra. This enhancement may be related to strengthened electron-phonon coupling and increased thermal population of ground state vibrational levels. A similar trend in CaWO₄ suggests that this phenomenon may be common among scheelite-type oxyanion compounds, providing a feasible approach for probing intrinsic absorption in strongly absorbing solids.