Improvement of Morphology and Luminescence Properties of Powellite Type Red Phosphors CaGd_1−xNbMoO₈: xEu³⁺ Synthesized via Citrate Gel Route

Abstract

Powellite type molybdate-based red phosphors CaGd 1Àx Nb-MoO 8 : xEu 3+ (x = 0.05, 0.1, 0.15, 0.20, 0.25, and 0.30) were synthesized by a solid-state reaction (SSR) route, and a citrate gel (CG) route. The crystalline structure, morphology, absorbance, and luminescent properties of these phosphors were characterized using powder X-ray diffraction, scanning electron microscopy, UV visible absorption spectroscopy, and photoluminescence spectroscopy. The solid solution formation of the phosphor effectively takes place at a lower temperature by the CG route than the SSR route. Particle morphology of the phosphors prepared by the CG route reveals that they are less agglomerated, more spherical, and homogenous in nature with uniform particle size. Investigations on photoluminescence properties show that these phosphors emit strong red light (614 nm) under both near UV (395 nm), and blue (465 nm) excitations. The morphological variation of the developed phosphors with respect to synthesis method and heat treatment played an important role in their luminescence enhancement. The red phosphors prepared via CG route were characterized by enhanced and sharper red emission with longer life time compared to that of phosphors synthesized via SSR route. The CIE color coordinates of the developed red phosphors are (0.65, 0.34) that are closer to NTSC standard red phosphor. Thus, these phosphors could be a promising red candidate for the phosphor converted white light emitting diode applications.

Characterization of powellite-based solid solutions by site-selective time resolved laser fluorescence spectroscopy

“…16 For either application, as a dielectric material or for the immobilization of nuclear waste, the efficacy of the material will depend on its stability. Material stability is again related to material properties such as crystallinity, phase purity, and distribution of the luminescent probe, 9 or radionuclide, respectively. The stability of a solid solution is to a large degree dependent on the stress induced in the lattice by the substitution.…”

“…The spectra for series members with 5% to 30% trivalent metal content are very similar; however, a detailed structural analysis was not performed as spectra lack the necessary resolution. 9 Mendoza et al also studied the early members of the solid solution series with up to 7% Ln 3+ substitution before and after irradiation by Ar and Pb ion beams. Once again the spectra show a strong hypersensitive effect.…”

Synthesis and luminescence of Eu3+‐doped in triple phosphate Ca8MgBi(PO4)7 with whitlockite structure

“…The spectra include a broad band (215–310 nm, centered around 260 nm) and sharp peaks (beyond 360 nm) for the absorptions at 319 nm ( 7 F 0,1 → 5 H 3,6 ), 362 nm ( 7 F 0,1 → 5 D 4 ), 382 nm ( 7 F 0,1 → 5 L 7 ), 394 nm ( 7 F 0 → 5 L 6 ), 414 nm ( 7 F 1 → 5 D 3 ) and 465 nm ( 7 F 0 → 5 D 2 ) . The broad absorption band centered at 260 nm can be attributed to the O 2− → Eu 3+ charge‐transfer band corresponding to electronic transition from the 2 p orbital of O 2− to the 4 f orbital of Eu 3+ . The charge‐transfer excitation increased with increasing Eu 3+ content, and the emission intensity of Ca 8 MgEu(PO 4 ) 7 , namely, x = 1.00, is much stronger than the others.…”

Structural and photoluminescence properties of stannate based displaced pyrochlore-type red phosphors: Ca3−xSn3Nb2O14:xEu3+

“…The sharp peaks beyond 360 nm are due to the intraconfigurational (f-f ) transitions of Eu 3+ including the peaks with maxima at 362 nm ( 7 F 0 -5 D 4 ), 382 nm ( 7 F 0 -5 G 2-4 ), 394 nm ( 7 F 0 -5 L 6 ), 412 nm ( 7 F 0 -5 D 3 ) and 464 nm ( 7 F 0 -5 D 2 ). 27 The f-f transition peaks are less intense compared to the broad charge transfer band and are saturated for 15 mol% doping. Among them, the intensity of the peaks at 394 nm and 464 nm excitation wavelengths which are emission lines of near UV and blue LED chips is much stronger than the other transitions from Eu 3+ .…”