A Novel Multifunctional Upconversion Phosphor: Yb ³⁺ /Er ³⁺ Codoped La ₂ S ₃

Abstract

Yb 3+ / Er 3+ codoped La 2 S 3 upconversion ( UC ) phosphors have been synthesized using high‐temperature solid‐state method. Under 971‐nm excitation, the maximum luminescence power can reach 0.64 mW at the excitation power density of 16 W/cm 2 and an absolute power yield of 0.36% was determined by an absolute method at the excitation power density of 3 W/cm 2 , and the quantum yield of La 2 S 3 : Yb 3+ , Er 3+ (green ~0.18%, red ~0.03%, integration ~0.21) was comparable to that of NaYF 4 : Yb 3+ , Er 3+ nanocrystals (integration ~0.005–0.30). Frequency upconverted emissions from two thermally coupled excited states of Er 3+ were recorded in the temperature range 100–900 K. The maximum sensitivity of temperature sensing is 0.0075 K −1 . As the excitation power density increases, the temperature of host materials rapidly rises and the top temperature can reach to 600 K. Given the intense UC emission, high sensitivity, as well as good photothermal stability, La 2 S 3 : Yb 3+ / Er 3+ phosphor can become a promising composite material for photothermal ablation of cancer cells possessing the functions of temperature sensing and in vivo imaging.