Upconversion luminescence and temperature sensing in novel CaLa₂ZnO₅:Ho³⁺/Yb³⁺ phosphors

Phosphors of the ternary metal oxide CaLa₂ZnO₅ host co-activated with Ho³⁺/Yb³⁺ were synthesized using the solution combustion method. X-ray powder diffraction carried out the phase confirmation for different doping concentrations. Surface morphology and elemental composition were assessed through field emission scanning electron microscope images and an energy-dispersive X-ray spectrum. Using a 980 nm laser for excitation, the up-conversion (UC) emission spectra were recorded at 500–800 nm. Photoluminescence measurements for emission between 1100 and 1300 nm were also made for the same excitation. The UC emission spectra recorded between 500 and 800 nm consisted of green, red, and near-infrared emission peaks characteristic of Ho³⁺ ions. It was found that the variation in Yb³⁺ concentration significantly affected the UC emission through energy transfer. Power-dependent UC measurements were also carried out for the recorded emission spectra. The temperature sensing capability of the synthesized phosphors was investigated for the non-thermally coupled levels ⁵F₄,⁵S₂ → ⁵I₈ and ⁵F₅ → ⁵I₈, using the fluorescence intensity ratio technique. The maximum values corresponding to the absolute and relative sensitivity were estimated to be 0.19 and 1.78 K⁻¹, respectively. The synthesized phosphor was found to have good thermal stability up to 473 K with an activation energy of 0.73 eV. The synthesized phosphor can, therefore, be efficiently used as a probe for temperature sensing, especially at high temperatures.