【Others Papers】Emergent optical and magnetic functionalities in Holmium-activated β-Ga₂O₃ nanoparticles

      Researchers from the Himachal Pradesh University have published a dissertation titled "Emergent optical and magnetic functionalities in Holmium-activated β-Ga₂O₃ nanoparticles" in Journal of Alloys and Compounds.

Abstract

      Holmium (Ho³⁺) - doped β-Ga₂O₃ nanoparticles (1–3 wt.%) were synthesized via a solid-state combustion route to investigate the evolution of structural, vibrational, optical, luminescent, and magnetic properties. X-ray diffraction confirms the monoclinic β-Ga₂O₃ phase, with the emergence of a minor Ho₃Ga₅O₁₂ phase at higher dopant concentrations, indicating a solubility limit between 1 and 2 wt.%. Williamson-Hall analysis reveals compressive strain at low doping followed by partial strain relaxation at higher concentrations due to ionic radius mismatch between Ho³⁺ (0.90 Å) and Ga³⁺ (0.62 Å) ions. Morphological analysis shows variations in grain size and distribution, while elemental mapping confirms uniform incorporation of Ho³⁺ within the host lattice. FTIR spectra exhibit shifts in Ga-O vibrational modes, indicating local lattice distortion around the dopant sites. Optical studies show a gradual shift of the absorption edge toward higher energy with slight bandgap widening, attributed to defect-state redistribution and suppression of band-tail states, along with characteristic intra-4f absorption of Ho³⁺ ions. Photoluminescence (PL) exhibits broad blue emission originating from intrinsic defect states, with progressive quenching upon Ho incorporation due to increased non-radiative recombination and modification of the defect landscape. In contrast, strong green upconversion (UC) emission is observed under 980 nm excitation, arising from intra-4f transitions of Ho³⁺ ions through a sensitizer-free two-photon excited-state absorption mechanism, with intensity increasing with dopant concentration. Time-resolved measurements indicate a dominant radiative relaxation pathway with microsecond lifetimes, while magnetic studies reveal predominantly diamagnetic and paramagnetic behavior with a weak ferromagnetic component, attributed to defect-mediated localized magnetic interactions. Notably, the observation of sensitizer-free green upconversion emission along with tunable defect-mediated optical and magnetic properties highlights the multifunctional nature of β-Ga₂O₃. These results demonstrate that Ho doping effectively tunes the defect structure and optoelectronic response of β-Ga₂O₃, highlighting its potential for multifunctional photonic applications.

DOI：

https://doi.org/10.1016/j.jallcom.2026.187828