Simultaneous negative thermal quenching luminescence of upconversion and downshifting processes in Al2(WO4)3:Yb/Er phosphors with low thermal expansion

Abstract

Avoiding thermal quenching (TQ) is still a huge challenge for the practical application of lanthanide (Ln³⁺)-doped luminescence materials. Herein, a novel Al₂(WO₄)₃:Yb³⁺/Er³⁺ (AWO:Yb/Er) phosphor with low-thermal-expansion is prepared via a coprecipitation method. Upon 980 nm laser excitation, the simultaneous negative thermal quenching luminescence of upconversion (UC) and downshifting (DS) processes is achieved in the temperature range from 298 to 573 K. The luminescence mechanism is systematically investigated through in situ temperature-dependent synchrotron X-ray diffraction and photoluminescence (PL) dynamics. Below 423 K, the thermal enhancement of the luminescence of AWO:Yb/Er is attributed to the continuous loss of quenching centers (water molecules). Above 423 K, the thermal enhancement of the luminescence of AWO:Yb/Er is attributed to the increased probability of radiative transitions. Based on the luminescence intensity ratio of the thermally coupled energy levels (TCLs) ²H_11/2/⁴S_3/2 and nonthermally coupled levels (NTCLs) ²H_11/2/⁴F_9/2 at different temperatures, the corresponding absolute and relative sensitivities were calculated. The absolute and relative sensitivities (NTCLs mode) of the targeted samples reach up to 10.5% K⁻¹ and 1.41% K⁻¹, respectively. The repeatability (R) is up to 95.1%. Our findings highlight a general approach for designing a thermally stable and cost-effective Ln³⁺-doped aluminate phosphor on UC/DS luminescence.