Tailoring thermal expansion and luminescence thermometric performance of KMgScW3O12-based compounds

Abstract

Negative thermal expansion (NTE) compounds provide an opportunity to understand the nature of thermal expansion and the engineering applications of inorganic solid functional materials. However, very few NTE materials have been found so far, which also restricts the unique applications of anomalous lattice effects in solving luminescence thermal quenching and ratio fluorescence temperature measurement. In this work, we have prepared (KMg)_xSc_2−xW₃O₁₂-based compounds with abnormal thermal expansion and luminescence negative thermal quenching. Their crystal structure, microstructure, thermal expansion properties, and semiconductor performance are studied by variable temperature X-ray diffraction, scanning electron microscopy, low-temperature differential scanning calorimetry, and UV-vis diffuse reflection spectroscopy. The thermal expansion can switch from positive to zero to negative by controlling the content of (KMg)³⁺ ions. Interestingly, the upconversion luminescence spectra intensity in (KMg)_xSc_2−xW₃O₁₂-based compounds displays unique negative thermal quenching, including weak negative thermal quenching and strong thermal quenching with the x from 0.4 to 0.8. The results of decay curves show that the trend of decay curves with temperature is consistent with the thermal expansion behaviour; the stronger the NTE properties, the stronger the luminescence negative thermal quenching. The maximum absolute sensitivity (S_a) of (KMg)_0.4Sc_1.42W₃O₁₂:0.15Yb/0.03Er is 0.50 × 10⁻² K⁻¹ at 385 K, and the maximum relative sensitivity (S_r) is 0.86% K⁻¹ at 298 K. This work does not only provide a new NTE material but also find that the NTE material as a luminescent host can produce a phenomenon of luminescence thermal enhancement.