Upconversion luminescence and temperature measurement performance of Ho3+/Yb3+ and Tm3+/Yb3+ codoped Na5Rb7Sc2(WO4)9 phosphors

Abstract

New series of Ho³⁺/Yb³⁺ and Tm³⁺/Yb³⁺ codoped Na₅Rb₇Sc₂(WO₄)₉ phosphors have been prepared by a conventional solid state reaction method. A powder XRD study has revealed that all the synthesized tungstates are isostructural and crystallize in the trigonal crystal system (sp. gr. R32, Z = 3). Upconversion luminescence in the 460–850 nm spectral range, associated with transitions in Ho³⁺ or Tm³⁺ ions, has been detected under 980 nm laser diode excitation. The optimal Ho³⁺/Yb³⁺ and Tm³⁺/Yb³⁺ ratios have been determined. Possible mechanisms of energy transfer between lanthanide ions have been discussed. The luminescence characteristics of the representative samples, Na₅Rb₇Sc_1.925Yb_0.045Ho_0.03(WO₄)₉ and Na₅Rb₇Sc_1.9Yb_0.09Tm_0.01(WO₄)₉, have been studied at 298–498 K to evaluate their temperature measurement performance. The calculated values of the absolute and relative sensitivities indicate that the studied tungstates are promising phosphors for non-contact thermometry.