Influence of K/Na ions on structure and luminescence properties of red phosphors K0.5Na0.5Gd(WO4)2: Eu3+

Abstract

In this paper, we demonstrated the influence of K/Na alkali ions on the structural and photo-cathodoluminescence properties of novel K0.5Na0.5Gd(WO4)2:Eu3+ red phosphor synthesized by the solid-state method. The purity of phosphors is determined from the X-ray diffraction. Rietveld refinement studies confirms that the compounds both K0.5Na0.5Gd(WO4)2:Eu3+ and NaGd(WO4)2:Eu3+ were crystallized in the tetragonal structure with I41/a space group and KGd(WO4)2:Eu3+ was crystallized in monoclinic structure with C2/c space group. The FTIR results indicate that the presence of characteristic functional groups in synthesized samples. The optical bandgap determined from the UV-Visible reflectance spectra in the order K0.5Na0.5Gd(WO4)2:Eu3+ Ω4 of JO parameters indicates the asymmetric environment around the activator suggesting the co-valency of Eu-O bonds with respect to host matrix. Radiative lifetime, branching ratio, electronic dipole transition probabilities were calculated based on the Judd-Ofelt formalism. Cathodoluminescence studies shows the characteristic emission of the Eu3+ ions for low current and voltage which further confirms the pure red color emission of phosphors. All the synthesized phosphors can emit the red emissions with correlated color temperature range from 1500 to 2000 K. For K0.5Na0.5Gd(WO4)2:Eu3+ sample the chromaticity coordinate (x = 0.667, y = 0.329) are closer to the NTSC trichromatic coordinated (x = 0.67,y = 0.33) than that of Y2O2S:Eu3+ suggesting that K0.5Na0.5Gd(WO4)2:Eu3+ can be a potential red phosphor material for warm white LED's applications.

Keywords

• Tungstates
• Rietveld refinemnet
• J-O analysis
• Luminescence