Concentration and pump power-mediated color tunability, optical heating and temperature sensing via TCLs of red emission in an Er3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor

Abstract

Intense red upconversion luminescence was observed in the Er³⁺/Yb³⁺/Li⁺ co-doped ZnGa₂O₄ phosphor synthesized through the solid state reaction method for the first time. The structural characterization showed a large crystalline nature and an increase in the particle size via Li⁺ doping. The absorption spectra showed a large number of peaks in the UV-vis-NIR regions due to the Er³⁺ and Yb³⁺ ions. The Er³⁺/Yb³⁺ co-doped ZnGa₂O₄ phosphor exhibited green, red and NIR upconversion emissions on excitation with 980 nm radiation. The intensity of the red emission was relatively larger than that of the other emissions. The luminescence intensity versus pump power measurements revealed the number of required photons for these emissions. The phosphor showed very interesting color tunability as a function of Er³⁺ ion concentration and incident pump power. The luminescence intensity of the Er³⁺/Yb³⁺ co-doped phosphor was enhanced more than two times via Li⁺ doping. The enhancement in the luminescence intensity was proposed to be due to the increase in the crystallinity and particle size of the phosphor. The lifetimes of the ⁴S_3/2 and ⁴F_9/2 levels also increased in the presence of Li⁺ ions. The variation in the fluorescence intensity ratio (FIR) of the thermally coupled levels (TCLs) of the red emission with incident pump power offered effective optical heating in the phosphor. The temperature-induced FIR using TCLs of red emission exhibited a larger value of temperature sensing sensitivity in the presence of Li⁺ ions, which was up to 14 × 10⁻⁴ K⁻¹. Thus, the Er³⁺/Yb³⁺/Li⁺ co-doped ZnGa₂O₄ phosphor may be used in photonic, optical heating, and temperature sensing devices.