Effect of annealing conditions on the luminescence properties and thermometric performance of Sr₃Al₂O₅Cl₂:Eu²⁺ and SrAl₂O₄:Eu²⁺ phosphors

Abstract

We report on the synthesis, photoluminescence optimization and thermometric properties of Sr₃Al₂O₅Cl₂:Eu²⁺ and SrAl₂O₄:Eu²⁺ phosphor powders. The photoluminescence of Sr_2.9Al₂O₅Cl₂:0.1Eu²⁺ phosphors exhibits a blue-shift with an increasing annealing temperature owing to a decrease in the crystal field strength of the host caused by evaporation of Cl from the material. The quenching of the blue band in favour of the red band observed in the luminescence spectra of Sr_2.9Al₂O₅Cl₂:0.1Eu²⁺ with an increased annealing temperature was explained using the mechanism of the Landau-Zener transitions. The quantum yield and the lifetime of the phosphors depend on the annealing temperature. Phosphor samples annealed at 850 °C, 1000 °C, 1200 °C and 1500 °C were found to be potential luminescence thermometers using the luminescence spectral method. For Sr₃Al₂O₅Cl₂:Eu²⁺ annealed at 1000 °C, the temperature-dependent dual-band intensity ratio demonstrated a high-temperature sensitivity of ∼1.47%/°C in the temperature range of 23 °C to 40 °C which is superior to other reported phosphors with a microsecond decay time, suggesting that the material has potential for sensitive thermometry applications at ambient temperatures.