Photoluminescence characterization and energy transfer between $\mathrm{WO}_{4}^{2-}$ groups and $\mathrm{Sm}^{{3}+}$ in $\mathrm{CaWO}_{4}{:}\mathrm{Sm}^{3+}$ phosphor

Abstract

$\mbox{Sm}^{3+}$-doped CaWO₄ phosphors with red light emission were successfully synthesized via high temperature solid state reaction. The obtained samples were characterized by the X-ray powder diffraction (XRD) method and the XRD data were analyzed by the Rietveld refinement method. The results illustrate that all the phases can be indexed to scheelite structure. Luminescence spectroscopy was carried out and decay curves as well as time-resolved photoluminescence spectra measured at room temperature were obtained. The results of the excitation spectra show that the optimal $\mbox{Sm}^{3+}$ concentration is different for both the intensity of the charge transfer band of $\mbox{WO}_{4}^{2-}$ and the characteristic transition of $\mbox{Sm}^{3+}$. What is more, the absorbed energy by $\mbox{WO}_{4}^{2-}$ groups could transfer to $\mbox{Sm}^{3+}$, but this energy transfer process is not thorough. The time-resolved PL spectra indicate not only the starting time of the energy transfer from $\mbox{WO}_{4}^{2-}$ groups to $\mbox{Sm}^{3+}$ ions, but also the time when the energy transfer reaches the maximum. A proposed explanation for the energy transfer is also discussed in detail.