Synthesis, dual mode luminescence and down-conversion based thermometric properties of novel Y2−x−yLaCaGa3ZrO12:xEr3+, yYb3+ phosphors

Abstract

Fluorescence thermometry is extensively utilized in many fields owing to its high efficiency and accuracy of detection. The fluorescence intensity ratio (FIR) using thermally coupled energy states of Er³⁺ is a promising route to produce thermometers with high spatial resolution and rapid response. Herein, Y_2−xLaCaGa₃ZrO₁₂:xEr³⁺ and Y_1.92−yLaCaGa₃ZrO₁₂:0.08Er³⁺, yYb³⁺ phosphors were synthesized using a solid-state reaction method. Their crystal structure, dual mode luminescence and potential for down-conversion (DC) temperature sensing application were investigated. With an increase in the Yb³⁺ ion concentration, the DC luminescence of Y_1.92−yLaCaGa₃ZrO₁₂:0.08Er³⁺, yYb³⁺ (0.05 ≤ y ≤ 0.5) phosphors under 374 nm excitation was significantly decreased, suggesting an efficient Er³⁺ → Yb³⁺ energy transfer (ET), which was supported by decay lifetime analysis and varified via calculating ET efficiency that significantly increased from 20% to 67%. Moreover, the temperature-dependent DC emission spectra (in the 78–525 K range) and their temperature-sensing properties (absolute and relative sensitivities) were evaluated using FIR technique. The highest S_A (0.001825 K⁻¹) and S_R (2.939% K⁻¹) for Y_1.92LaCaGa₃ZrO₁₂:0.08Er³⁺ were obtained at 425 K and 200 K, respectively. Conversely, for Y_1.72LaCaGa₃ZrO₁₂:0.08Er³⁺, 0.2Yb³⁺, even with a lower S_A (0.001582 K⁻¹ at 500 K), the S_R value was enhanced significantly to 1209/T² (200–300 K) and 990.7/T² (300–525 K) from 1175/T² (200–300 K) and 883.1/T² (300–525 K), respectively, for Y_1.92LaCaGa₃ZrO₁₂:0.08Er³⁺. The highest S_R was observed to be 2.939 and 3.023% K⁻¹ for Y_1.92LaCaGa₃ZrO₁₂:0.08Er³⁺ and Y_1.72LaCaGa₃ZrO₁₂:0.08Er³⁺, 0.2Yb³⁺ thermometers, at 200 K with the lowest thermal resolution of 0.17 and 0.16, respectively, which is quite high as compared to the other reported thermometers. Therefore, we believe that the phosphors under investigation are promising candidates for non-contact mode temperature sensing application.