Tm³⁺ Modified Optical Temperature Behavior of Transparent Er³⁺-Doped Hexagonal NaGdF₄ Glass Ceramics

Er³⁺-doped and Er³⁺-Tm³⁺-co-doped transparent hexagonal NaGdF₄ glass ceramics are fabricated via melt-quenching method. The emissions of Er³⁺-doped NaGdF₄ glass ceramics are adjusted from the green to red by varying the concentration of Tm³⁺ ion under the excitation of 980 nm. The spectrum, thermal quenching ratio, fluorescence intensity ratios, and optical temperature sensitivity of the transparent glass ceramics are observed to be dependent on the pump power. The maximum value of relative sensitivity reaches 0.001 K^-1 at 334 K in Er³⁺-doped NaGdF₄, which shifts toward the lower temperature range by co-doping with Tm³⁺ ions, and has a maximum value of 0.00081 K^-1 at 292 K. This work presents a method to improve the optical temperature behavior of Er³⁺-doped NaGdF₄ glass ceramics. Moreover, the relative sensitivity S_R is proved to be dependent on the pump power of 980-nm lasers in Er³⁺-doped NaGdF₄ and Er³⁺-Tm³⁺-co-doped NaGdF₄.