Optical thermometry based on the upconversion fluorescence from Yb3+/Er3+ codoped La2O2S phosphor

The fluorescence intensity ratio (FIR) of the two green emission bands centered at 524 and 547 nm in Yb3+/Er3+ co-doped La2O2S phosphor was studied as a function of temperature in the range 300–573 K for optical temperature measurement. Upconversion phosphor La2O2S: Yb3+, Er3+ show intense double-band green emission at low pump power, and the maximum sensor sensitivity derived from the FIR of the upconversion green emissions was approximately 0.008 K−1. This indicates that the phosphor has potential application in optical temperature sensors. Based on the Judd–Ofelt theory, an interpretation on how the factors influence the sensitivity of temperature sensing was proposed for the first time.