Green-Emitting Er3+-Doped Ca2Al2O5 Phosphors for Optical Thermometry and LED Applications

A series of novel Er3+-doped calcium aluminate phosphors were successfully synthesized using a high-temperature solid-state reaction method. Structural characterization through x-ray diffraction (XRD) confirmed phase formation and enabled the determination of lattice parameters. Photoluminescence (PL) emission studies indicated that the optimal doping concentration was 2 mol.%, beyond which concentration quenching occurred, as evidenced by Dexter’s theory. The chromaticity coordinates derived from CIE data placed the emission in the green region, with correlated color temperature (CCT) values between 5888 K and 5954 K. Ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy showed a reduction in the optical bandgap from 4.91 eV to 4.80 eV upon Er3+ doping, attributed to the formation of new energy levels. Temperature-dependent PL (TDPL) spectra demonstrated stable green emission up to 483 K, with an activation energy of 0.18 eV. Fluorescence intensity ratio (FIR) analysis confirmed the phosphor’s potential for optical thermometry, yielding maximum absolute sensitivity of 0.0131 K−1 at 403 K and peak relative sensitivity of 1.07% K−1 at 343 K. Furthermore, the phosphor exhibited excellent thermal stability, maintaining structural integrity up to 700°C and a thermal quenching temperature of 363 K. These findings highlight Ca2Al2O5:xEr3+ as a promising candidate for applications in green light-emitting diodes (LEDs) and non-contact optical temperature sensing.