Optimal Doping of Ho3+ in CaTiO3 Perovskite for Enhanced Photoluminescence and Sustainable Green Emission

In this work, the synthesis of Ho 3+ -doped calcium titanate perovskite (CaTiO 3 ) revealed significant photoluminescence (PL) properties, predominantly displaying a distinct green emission. The investigation explored Ho 3+ -doped CaTiO 3 perovskite synthesized via the sol–gel method. Structural analysis confirmed an orthorhombic crystal structure through powder x-ray diffraction (XRD) and Rietveld refinement, while Fourier transform infrared (FT-IR) spectroscopy confirmed the presence of functional groups in Ho 3+ -doped CaTiO 3 . Diffuse reflectance spectroscopy (DRS) revealed a charge transfer band between O 2− and Ho 3+ ions in the range of 250–350 nm, supported by photoluminescence excitation (PLE) spectra. A bandgap of 3.39 eV was found for Ho 3+ -doped CaTiO 3 . At 0.03 mol Ho 3+ , the PLE band intensity was saturated, indicating optimal excitation efficiency. Emission spectra revealed distinct intra 4 f –4 f transitions, particularly a green emission at 545 nm under 454 nm excitation corresponding to 5 F 4 + 5 S 2 → 5 I 8 transition. The PL intensity reached its peak at 0.03 mol Ho 3+ and then decreased due to concentration quenching. Color purity reached ~90%, highlighting its potential in applications requiring precise green emission. The results of the study suggest that this perovskite is well suited for optoelectronics, lighting, displays, or industries that require specific green light emission properties.