Optical thermometry based on the thermal coupling of low-lying levels of Sm3+ in highly stable NaGdF4 glass ceramics

Abstract Based on a new scheme of ground state thermal coupling, high sensitive temperature sensing has been realized in the Sm3+ doped hexagonal NaGdF4 glass with high thermal stability. Two processes were used to create a temperature sensor with a wide temperature operating range and high relative sensitivity. Under resonance excitation, Sm3+ was directly populated to 4G5/2 from thermally activated 6H7/2 (process A) and 6H9/2 (process B) rather than ground state 6H5/2. The increase in the anti-Stokes luminescence intensity from 4G5/2 with temperature was proposed to determine temperature. Relative sensitivity is 139,300/T2 (%/K) at 303.6–570 K for process A and 282,300/T2 (%/K) at 390–773 K for process B. The proposed approach not only effectively eliminates the heating effect caused by a laser and background Stokes-type scattering noise but also provides high quantum efficiency because of the one-photon excitation process. Combine the advantages of high thermal stability of glass and low phonon energy of fluoride, NaGdF4:Sm3+ glass ceramics have considerable potential applications in fiber optic temperature sensing with a wide temperature range and high sensitivity.