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

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, Y2−xLaCaGa3ZrO12:xEr3+ and Y1.92−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 Y1.92−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 SA (0.001825 K−1) and SR (2.939% K−1) for Y1.92LaCaGa3ZrO12:0.08Er3+ were obtained at 425 K and 200 K, respectively. Conversely, for Y1.72LaCaGa3ZrO12:0.08Er3+, 0.2Yb3+, even with a lower SA (0.001582 K−1 at 500 K), the SR 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 Y1.92LaCaGa3ZrO12:0.08Er3+. The highest SR was observed to be 2.939 and 3.023% K−1 for Y1.92LaCaGa3ZrO12:0.08Er3+ and Y1.72LaCaGa3ZrO12:0.08Er3+, 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.