Optical Thermometry Based on Fluorescence Intensity Ratio in Dual-Phases Glass Ceramics Containing LiYF₄: Ln³⁺(Ln=Tb, Dy) and ZnAl₂O₄: Cr³⁺ Nanocrystals

Dual-phases glass ceramics (GCs) containing LiYF₄: Ln³⁺(Ln=Eu, Tb, Dy) and ZnAl₂O₄: Cr³⁺ nanocrystals (NCs) were fabricated by a conventional melt-quenching method. The structural and spectrographic characterizations indicate that Ln³⁺ can be doped into LiYF₄ lattice and Cr³⁺ can be introduced into ZnAl₂O₄ lattice, respectively. In this regard, the luminescent centers are physically separated through a spatial isolation strategy, getting rid of adverse energy transfer processes. The dual-modal luminescence of Ln³⁺ and Cr³⁺ can be thus attained simultaneously. Also, optical thermometry based on the fluorescence intensity ratio (FIR) of Ln³⁺/Cr³⁺ is performed. Under irradiation upon 377 nm, the FIR value for Tb³⁺: ⁵D₄→⁷F₅ and Cr³⁺: ²E→⁴A₂ transitions varies acutely, with a maximal relative sensitivity of 0.80%·K^–1 at 570 K. The FIR-based optical thermometry for Dy³⁺: ⁴F_9/2→⁶H_13/2 and Cr³⁺: ²E→⁴A₂ transitions is carried out, with a maximal relative sensitivity of 0.86%·K^–1 at 573 K. As a consequence, the dual-phases GCs can be an ideal medium for the spatial isolation of luminescent centers, suppressing an adverse energy transfer process and realizing an efficient dual-mode luminescence. This is beneficial to the application of FIR-based optical thermometry for GC materials.