Review on the synthesis, structural and photo-physical properties of Gd₂O₃ phosphors for various luminescent applications

Inorganic lanthanide oxides are promising host lattices owing to their stable chemical and physical stability, large Stoke shifts, absence of photobleaching, and low phonon energy. Among the various lanthanide oxides, Gd₂O₃ has fascinated the modern era with its single-phase multimodal nature. Due to the presence of seven unpaired electrons in the f-orbitals of Gd³⁺ ions, it shows superparamagnetic behavior than the other oxides. It exhibits sharp, narrow, and intense spectra when doped with different rare-earth (Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) and non-rare-earth (Bi, Mn) elements. The dual luminescence and paramagnetic behavior make it a bi-functional material due to which it finds vast applications in optoelectronic devices, field emission displays, bio-sensors, bio-probes, and MRI contrast agents. The present article encompasses mainly structural analysis, synthesis, and spectroscopic investigations of doped and undoped Gd₂O₃ phosphors for various applications. This review article is fundamentally distributed into four parts. In the first part, different synthesis routes of Gd₂O₃ are reviewed, and their resulting outcomes are compared. In the second part, different structures of Gd₂O₃ with site occupancy of metal ions are discussed. Then, the different spectroscopic and optical properties of doped and undoped Gd₂O₃ are illustrated. The consequences of the different factors on the luminescent properties and energy transfer mechanisms in Gd₂O₃ phosphors are also discussed. The last part of the review article is devoted to the applications of Gd₂O₃ phosphors in various fields.