Dualistic temperature sensing in Er³⁺/Yb³⁺ doped CaMoO₄ upconversion phosphor

Temperature sensing performance of Er³⁺/Yb³⁺ doped CaMoO₄ phosphor prepared via polyol method is reported herein. The X-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy are done to confirm the phase, structure and purity of the synthesized phosphor. The infrared to green upconversion emission is investigated using 980nm diode laser excitation along with its dependence on input pump power and external temperature. The temperature dependent fluorescence intensity ratio of two upconversion emission bands assigned to ²H_11/2→⁴I_15/2 (530nm) and ⁴S_3/2→⁴I_15/2 (552nm) transitions has shown two distinct slopes in the studied temperature range - 300 to 760K and therefore, dual nature of temperature sensitivity is observed in this phosphor. This phenomenon in rare earth doped materials is either scarcely reported or overlooked. The material has shown higher sensitivity in the high temperature region (535K-3K^-1 at 535K. The results indicate potential of CaMoO₄: Er³⁺/Yb³⁺ phosphor in high temperature thermometry.