Characterization and Investigation of the UCPL, Photoluminescence, and Thermoluminescence Properties of Neodymium-Doped Silicates

This paper reports the spectral and kinetic features of the up- and downconversion photoluminescence (PL) of (1%, 2%, 3%, 4%, and 5%) Nd-doped BaSrSiO₄ silicates to elucidate the fundamental processes of UCPL. This manuscript discusses the energy transition levels and potential excitation processes. The sol-gel method was utilized for synthesizing Nd-doped BaSrSiO₄ nanocrystals, which were then annealed at 600 °C to produce silicates. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to determine the crystal phase and nanocrystal formation of the synthesized Nd-doped BaSrSiO₄ powders. When activated by various UV–visible wavelengths, the PL downconversion (DCPL) from a sample exhibits well-resolved bands with sub-split lines centered at 890 nm associated with the near-infrared transitions in Nd³⁺ ions. Quenching occurred at 5% doping due to multipolar interactions, indicating that 4% doping is appropriate for temperature sensing applications. Conversely, a visible upconversion PL (UCPL) has been found when excited by a pulsed laser of 800 nm. Furthermore, the suggested energy levels for the upconversion process were verified using the UCPL and photoluminescence excitation (PLE) data. Our results imply that the excited-state absorption mechanism (ESA) in rare earth (Nd)-doped BaSrSiO₄ is most likely a potential mechanism of the UCPL process. The TL glow peak shows the highest intensity for 4 mol% Nd³⁺-doped BaSrSiO₄ at 88 °C. Quenching at 5% was observed due to the dissipation of the trapping centers.