Optical Nanoarchitectonics of Highly Enhanced Asymmetric Ratio in Gd 2 O 3 :Eu 3+ Nanoparticles by Bi 3+ Codoping

We report the synthesis and comprehensive characterization of Eu 3+ (5 atom %) and Bi 3+ (10 atom %)-codoped Gd 2 O 3 nanoparticles (NPs) as a red emitter having a high asymmetric ratio of electric dipole transition to magnetic dipole transition. The nanoparticles have been synthesized from metal precursors in the presence of urea and ethylene glycol at 150 °C and annealed at 500–800 °C. X-ray diffraction (XRD) confirmed the formation of a cubic Gd 2 O 3 phase (space group Ia 3̅) with crystallite sizes increasing from 20 to 43 nm upon annealing. High-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) analyses verify the nanocrystalline structure and morphology, while energy dispersive X-ray spectroscopy (EDS), X-ray fluorescence (XRF), and Fourier transform infrared (FTIR) spectroscopy confirm the elemental composition and chemical bonding environment. Photoluminescence properties of Gd 2 O 3:Eu–Bi samples annealed at 500, 600, 700, and 800 °C are thoroughly studied and their energy transfer processes are discussed. The dynamic nature of energy transfer between the sensitizer (Bi 3+ ) and activator (Eu 3+ ) is investigated. A high asymmetric ratio value of 12.53 is obtained, which is more than those of the reported ones. The Commission Internationale de l’Eclairage (International Commission on Illumination, CIE) coordinates, the correlated color temperature (CCT), and color indexing are calculated from photoluminescence spectra, and light from blue to green to red is obtained from various UV range excitations.