Negative and positive thermal expansion effects regulate the upconversion and near-infrared downshift luminescence for multiparametric temperature sensing

Rare earth-doped luminescent materials suffer from thermal quenching (TQ) at high temperatures, greatly limiting their application in the high-temperature region. In this work, we prepared Yb2W3O12:Er negative thermal expansion (NTE) materials, achieving thermal enhancement of upconversion (UC) and near-infrared (NIR) downshift (DS) luminescence upon 980-nm excitation. When the temperature increased from 293 to 573 K, the green UC luminescence of Er3+ increased by 27 times, and the NIR DS luminescence increased by 87 times. The in situ temperature-dependent X-ray diffraction showed that the unit cell volume of Yb2W3O12:Er3+ samples decreased as the temperature increased, which reduced the distance between rare earth ions and increased the energy transfer. We further prepared NTE Yb2W3O12:Er phosphor and positive thermal expansion (PTE) CaWO4:Yb/Er phosphor, which enhanced the relative luminescence intensity through thermal enhancement of NTE Yb2W3O12:Er phosphor and TQ of PTE CaWO4:Yb/Er phosphor. The mixed phosphor addresses the limitations of TQ and thermal coupling energy of temperature sensors for non-contact fluorescence intensity ratio (FIR) thermometers. The maximum relative sensitivity (Sr) was 2.04% K−1, 2.15% K−1, 2.01% K−1, and 2.09% K−1 in the infrared-red FIR (I860/I525, I860/I675, I1550/I525, and I1550/I675), respectively, indicating its practical application in temperature sensors.