A dual-mode temperature sensing based on UC luminescence of a new green Er3+: SrLaGaO4 phosphor

Novel green-emitting SrLa_(1-x)Er_xGaO₄ (x = 1, 2, 3, 4, and 5 at.%) ceramic phosphors have been successfully synthesized through a solid-state reaction method. The up-conversion (UC) emission spectra of Er³⁺ ions were recorded under two excitation wavelengths (973 and 1550 nm). Two important parameters, correlated color temperature (CCT) and color purity/ Color Rendering Index (CRI), were calculated from the luminescence spectra, resulting in the highest values of CCT (between 5000 and 6000 K) and CRI (ranging from 90 to 97.4). The temperature dependence of Er³⁺ emission in the visible and infrared domains was investigated using the luminescence intensity ratio (LIR) method for thermally coupled levels (TCLs) and nonthermally coupled levels (NTCLs) under both excitation wavelengths. The highest relative sensitivity (S_r) values were achieved for the 1% Er: SLO sample, with S_r = 1.38% K^-1 at 300 K from TCLs (²H_11/2/⁴S_3/2) under λ_ex = 973 nm. Under the 1550 nm excitation wavelength, the peak value of S_r = 1.09% K^-1 at 300 K was observed from TCLs for the 1% Er: SLO sample, along with S_r = 0.98% K^-1 at 575 K from NTCLs for the 3Er: SLO sample. In the infrared domain, the maximum S_r value for 1% Er: SLO was recorded at S_r = 0.88% K^-1 at 75 K, indicating that Er: SrLaGaO₄ phosphors possess the potential to function as optical temperature sensors and can be utilized in white light-emitting diode devices.