Synthesis and up-conversion luminescence of Yb3+/Er3+/Tm3+ doped Ca9Y(PO4)7

Abstract

Samples of Ca₉Y(PO₄)₇ co-doped with Yb³⁺/Er³⁺, Yb³⁺/Tm³⁺, or Yb³⁺/Er³⁺/Tm³⁺ have been synthesized through two different routes, i.e. a modified hydrothermal method, followed by annealing in air at 850 °C and a solid-state reaction. The results of SEM and TEM show that the particle size of the samples synthesized by the solid state reaction method is about several micrometers, while that of the sample synthesized by the modified hydrothermal method is around 180 nm. The up-conversion luminescence of samples is studied as a function of different Yb³⁺, Er³⁺, Tm³⁺ ion concentrations and laser powers. Under 980 nm laser excitation, samples of Yb³⁺/Er³⁺ co-doped Ca₉Y(PO₄)₇ generate green and red emissions, while samples co-doped by Yb³⁺/Tm³⁺ generate blue and red emissions. The red emission is most intense in Yb³⁺/Er³⁺ co-doped samples, while blue emission is predominant in Yb³⁺/Tm³⁺ co-doped samples. The main mechanism that allows for the up-conversion observed in Yb³⁺/Er³⁺, Yb³⁺/Tm³⁺ or Yb³⁺/Er³⁺/Tm³⁺ doped Ca₉Y(PO₄)₇ is attributed to the energy transfer among Yb³⁺ and the various Er³⁺/Tm³⁺ ions in excited states.