Energy transfer and multicolour photoluminescence in phosphors La2O3 doped by Tm3⁺, Ho3⁺, and Eu3⁺ for white LED and security applications

As the world evolves, the demand for efficient lighting sources is rising rapidly, and to cater to the burgeoning demand for swift expansion, technological advancement in white light-emitting diodes (WLEDs) and lighting materials is crucial. In this work, the photoluminescence of La₂O₃ single-doped (Tm, Ho, Eu), double-doped and triple-doped phosphors prepared by combustion synthesis was studied. XRD confirms hexagonal phase (-P6c2c) with lattice contraction on doping, supported by Rietveld refinement, while SEM shows agglomerated particles (~ 12 µm) and FTIR confirms La-O bonding. Under UV excitation, Tm³⁺, Ho³⁺ , and Eu³⁺ give blue, green, and orange-red emission, respectively; in Ho³⁺ doped samples, the small ⁵F₄-⁵S₂ gap (~ 200 cm⁻¹) compared to host phonon energy (~ 400 cm⁻¹) leads to merged emission. Efficient energy transfer (Tm → Ho, Ho → Eu, Tm → Eu) is observed in co-doped and tri-doped systems, with La₂O₃:Tm/Ho/Eu phosphor showing a strong red component. These results suggest La₂O₃-based phosphors are promising candidates for WLEDs, barcode security, and multicolour LED applications.