Er~(3+)-Yb~(3+)-Na~+:ZnWO_4 phosphors for enhanced visible upconversion and temperature sensing applications

The crystal structure and surface morphology of the Er³⁺/Yb³⁺/Na⁺:ZnWO₄ phosphors synthesized by solid state reaction method were analyzed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) analysis. The frequency upconversion (UC) emission study in the developed phosphors was investigated by using 980 nm laser diode excitation. The effect of codoping in the Er³⁺:ZnWO₄ phosphors on the UC emission intensity was studied. The UC emission bands that are exhibited in the blue (490 nm), green (530, 552 nm), red (668 nm) and NIR (800 nm) region correspond to the ⁴F_7/2→⁴I_15/2, ²H_11/2, ⁴S_3/2→⁴I_15/2, ⁴F_9/2→⁴I_15/2 and ⁴I_9/2→⁴I_15/2 transitions, respectively. The temperature sensing performance of the Er³⁺-Yb³⁺-Na⁺:ZnWO₄ phosphors was investigated based on the ²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 thermally coupled transitions of the Er³⁺ ions. The photometric study was also carried out for the developed phosphors.