Exploring effect of excitation wavelength on upconversion emission in Nd, Yb, Er and Ho tetra co-doped Y2O3 phosphor and use in optical thermometry

Abstract

This paper examines the effects of excitation wavelength, power, and temperature on the upconversion (UC) emission of phosphors prepared by doping Y 2 O 3 with combinations of four rare earth ions (Nd 3+ , Yb 3+ , Er 3+ , and Ho 3+ ) synthesised via the combustion route. Structural investigations were carried out using powder X-ray difraction and Rietveld refinement confirming all prepared phosphors retain the cubic crystal structure of the Y 2 O 3 host. Optical study confirms high transparency in the UV–visible–NIR region along with characteristic absorption bands corresponding to Nd 3+ , Yb 3+ , Er 3+ , and Ho 3+ ions. The UC emission was investigated under excitations of 980 nm (166 mW) and 932 nm (variable power) diode lasers. The emission spectra reveal UC emissions corresponding to Ho 3+ and Er 3+ , with Nd 3+ influencing the results. A wavelength-dependent effect was observed, with 980 nm excitation UC emissions are produced in both the red and green bands, while 932 nm excitation enhances the green band emission. These findings suggest potential applications in medical and security fields with 932 nm excitation. The power dependence of UC emission was also studied, showing that emission intensity increases with excitation power. The analysis of the excitation power-dependent intensity relationship indicates a deviation from the conventional two-photon absorption process because of presence of multiple excitation pathways. Thermal quenching of UC emission was studied, and Er 3+ , Nd 3+ , and Yb 3+ co-doped Y 2 O 3 phosphors demonstrated the highest absolute and relative sensitivities 0.0615 and 0.0113 K −1 , respectively among the samples, making them suitable for optical thermometry.