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

Abstract

• β-NaGdF 4 :Sm 3+ glass ceramics with high silica content are fabricated. • Emission intensity of Sm 3+ is enhanced 4.5 times after crystallization. • Two processes based on a novel strategy are applied to temperature sensing. • The sensitivities are 1393/T 2 and 2823/T 2 for process A and B, respectively. Based on a new scheme of ground state thermal coupling, high sensitive temperature sensing has been realized in the Sm 3+ doped hexagonal NaGdF 4 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, Sm 3+ was directly populated to 4 G 5/2 from thermally activated 6 H 7/2 (process A) and 6 H 9/2 (process B) rather than ground state 6 H 5/2 . The increase in the anti-Stokes luminescence intensity from 4 G 5/2 with temperature was proposed to determine temperature. Relative sensitivity is 139,300/T 2 (%/K) at 303.6–570 K for process A and 282,300/T 2 (%/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, NaGdF 4 :Sm 3+ glass ceramics have considerable potential applications in fiber optic temperature sensing with a wide temperature range and high sensitivity.