A comparative study of a tunable body-centered cubic (I) red-emitting nanophosphor for warm WLED applications

Abstract

Rare earth (RE) elements activated red-emitting nanophosphors have promising applications in the fabrication of white LEDs. To achieve red emission, we successfully synthesized Y2O3:Eu3+ and Li+ ​activated Y2O3:Eu3+ red-emitting nanophosphors employing chemical co-precipitation techniques at different annealing temperatures. The X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy, time-decay, High-resolution TEM, and photoluminescence (PL) spectroscopy have been studied to compare structural and optical characteristics. X-ray diffraction reveals that the nanophosphor has a single body-centered cubic (I) phase with point group symmetry m-3 (Number 206, Z ​= ​16). The crystal structures were modeled using the Rietveld refinement method at centrosymmetric and noncentrosymmetric sites of the host matrix. The FTIR spectra and HR TEM results reveal that the nanophosphors are polycrystalline and have high crystallinity. The optical bandgap of Y2O3:Eu3+ nanophosphor is lowered from 5.8 ​eV to 5.6 ​eV when Li+ ​ions are added, according to UV–Vis spectroscopy. PL investigations demonstrate a considerably increased emission band due to the flux effect, oxygen vacancy, and greatly improved crystallinity caused by the Li+ ​ion under varied excitation wavelengths. The optimal emission intensity was observed at 613 ​nm for all instances due to the 5D0→7F2 electric dipole transition of Eu3+ ions at annealed temperature 1000 ​°C. This is 1.44 times greater enhancement excited at 255 ​nm, 1.62 times higher at 393 ​nm, and 0.51 times higher at 466 ​nm when compared to noncodoped Li+ ​nanophosphor. The average lifetime corresponding to the 5D0→7F2 transition of Eu3+ ion improves with increasing annealing temperature and is found to be somewhat longer than that of a noncodoped phosphor. The estimated CIE 1931 chromaticity coordinates were tuned within the red region of the color space and CCTs were less than 3000 ​K under different excitation wavelengths. This implies that the materials could act as potential red-emitting nanophosphor for the fabrication of warm WLEDs.