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

In this work, the synthesis of Ho³⁺-doped calcium titanate perovskite (CaTiO₃) revealed significant photoluminescence (PL) properties, predominantly displaying a distinct green emission. The investigation explored Ho³⁺-doped CaTiO₃ 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 Ho³⁺-doped CaTiO₃. Diffuse reflectance spectroscopy (DRS) revealed a charge transfer band between O²⁻ and Ho³⁺ ions in the range of 250–350 nm, supported by photoluminescence excitation (PLE) spectra. A bandgap of 3.39 eV was found for Ho³⁺-doped CaTiO₃. At 0.03 mol Ho³⁺, the PLE band intensity was saturated, indicating optimal excitation efficiency. Emission spectra revealed distinct intra 4f–4f transitions, particularly a green emission at 545 nm under 454 nm excitation corresponding to ⁵F₄ + ⁵S₂ → ⁵I₈ transition. The PL intensity reached its peak at 0.03 mol Ho³⁺ 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.