Optical properties and Judd–Ofelt analysis of Nd₂O₃ nanocrystals embedded in polymethyl methacrylate

PMMA matrices were doped with nano-crystalline neodymium oxides synthesized by thermal decomposition process. X-ray diffraction and high-resolution transmission electron microscopy measurements were carried out to investigate the structure, phase, and the morphology of the Nd₂O₃ nanocrystals and those embedded in the PMMA matrix. The average grain sizes were estimated 35 ± 6 nm and 46 ± 4 nm for non-annealed and annealed Nd₂O₃ particles, respectively. The grain size distributions (GSD) were calculated from the diffraction peaks of the annealed and non-annealed Nd₂O₃ powders and doped PMMA samples. The mass density, refractive index, UV–Visible absorption spectra were measured and the data were analyzed using the Judd–Ofelt approach to determine the oscillator strengths, the spontaneous emission probabilities and the branching ratios as a function of the nano-crystalline Nd₂O₃ content in the range of 0.1 wt.%–20 wt.% of MMA. Luminescence spectra upon 808 nm diode laser excitation were carried out in the wavelength range of 850–1550 nm at room temperature. The photoluminescence study has shown that the reasonably sharp emission peaks were observed upon heat treatment at 800 °C for 24 h for all concentrations of Nd₂O₃ nanopowders in PMMA. The infrared laser transition of Nd³⁺ ions at about 1.06 μm due to the ⁴F_3/2 → ⁴I_11/2 transition was analyzed and discussed in Nd₂O₃ system for their possible applications in the photonic technology.