Neodymium doped lanthanum oxysulfide as optical temperature sensors

The fluorescence intensity ratio (FIR) technique for temperature sensing has been demonstrated in La₂O₂S:Nd³⁺ phosphors. The phosphors were extensively characterized using various methods such as X-ray diffraction, photoluminescence excitation, and photoluminescence spectra. Upon ultraviolet-visible (UV-vis) or near-infrared (NIR) light excitation, two intense NIR emissions of Nd³⁺ peaking at 897 nm and 1074 nm corresponding to transitions of ⁴F_3/2→ ⁴I_9/2 and ⁴F_3/2→ ⁴I_11/2 were generated at room temperature. NIR emission of Nd³⁺ in a wide temperature range from 30 K to 600 K was investigated. Experimental results show that the temperature evaluation can be realized by monitoring the emission peak position, measuring the fluorescence intensity ratio of ⁴F_5/2 and ⁴F_3/2 or that of the two Stark components of the ⁴F_3/2 level in the bulk La₂O₂S:Nd³⁺. Furthermore, the effective energy difference of the thermalized levels ⁴F _5/2 and ⁴F_3/2, and ⁴F_3/2 two Stark components were 987 cm^-1 and 110 cm^-1, respectively. Those results imply that La₂O₂S:Nd ³⁺ phosphor is a potential candidate for the optical temperature sensor.