Dy3+/Eu3+ co-doped CsGd(MoO4)(2) phosphor with tunable photoluminescence properties for near-UV WLEDs applications

A series of color tunable Dy3+/Eu3+ co-doped CsGd(MoO4)(2)(CGM) phosphors were prepared by the conventional solid state reaction. The crystal structure, morphology, vibrational modes, luminescence properties and energy transfer mechanism were investigated. Upon near ultraviolet `(n-UV) excitation, Dy3+/Eu3+ co-doped phosphors exhibit the characteristics blue (F-4(9.2) -> H-6(15/2)), yellow (F-4(9.2) -> H-6(13/2)) and red (D-5(0) -> F-7(2)) emission corresponding to transitions of Dy3+and Eu3+ions. By changing the doping concentration of Dy3+ and Eu3+, the emission hue could be controlled via the energy transfer mechanism. The energy transfer efficiency and critical distance of Dy3+ and Eu3+ have been calculated. The calculated chromaticity coordinates and color correlated temperature of co-doped phosphors lie at the F-4 warm white points of standard illuminants. (C) 2016 Elsevier Ltd. All rights reserved

Dy3+/Eu3+ co-doped CsGd(MoO4)(2) phosphor with tunable photoluminescence properties for near-UV WLEDs applications

A series of color tunable Dy3+/Eu3+ co-doped CsGd(MoO4)(2)(CGM) phosphors were prepared by the conventional solid state reaction. The crystal structure, morphology, vibrational modes, luminescence properties and energy transfer mechanism were investigated. Upon near ultraviolet `(n-UV) excitation, Dy3+/Eu3+ co-doped phosphors exhibit the characteristics blue (F-4(9.2) -> H-6(15/2)), yellow (F-4(9.2) -> H-6(13/2)) and red (D-5(0) -> F-7(2)) emission corresponding to transitions of Dy3+and Eu3+ions. By changing the doping concentration of Dy3+ and Eu3+, the emission hue could be controlled via the energy transfer mechanism. The energy transfer efficiency and critical distance of Dy3+ and Eu3+ have been calculated. The calculated chromaticity coordinates and color correlated temperature of co-doped phosphors lie at the F-4 warm white points of standard illuminants. (C) 2016 Elsevier Ltd. All rights reserved

White luminescence in Dy3+ doped BiOCl phosphors and their Judd-Ofelt analysis

White-light emitting Dy3+ doped layered BiOCl phosphors were synthesized by the solid state route and their structure was confirmed by the Rietveld refinement method. On substitution of Dy3+ ion to Bi3+-site in BiOCl, the photoluminescence spectra exhibit blue (F-4(9/2) -> H-6(15/2)), yellow (F-4(9/2) -> H-6(13/2)) and red (F-4(9/2) -> H-6(11/2)) emissions which function together to generate white light. It was found that the emission intensity increases up to 9 mol% of Dy3+ and then quenched due to dipole-dipole interaction. Judd-Ofelt theory and radiative properties suggest that the present phosphors have a long lifetime, high quantum efficiency, excellent color purity and better stimulated emission cross-section compared to reported Dy3+ doped compounds. The obtained color chromaticity results are close to the National Television System Committee standard and clearly establish the bright prospects of these phosphors in white luminescence. (C) 2015 Elsevier Ltd. All rights reserved

Synthesis and characterization of Sm3+ activated La1-xGdxPO4 phosphors for white LEDs applications

A series of orange-red light emitting Sm3+ activated La1-xGdxPO4 (0.00 x 1.00) phosphors were synthesized by the solid-state method. The structural parameters were confirmed by the Rietveld refinement method based on powder X-Ray diffraction (XRD) analysis. All the compounds crystallized in the monazite monoclinic structure with space group P 1 2(1)/n 1 (no. 14). The photoluminescence spectra of La0.95-xGdxPO4:Sm3+ phosphors were measured at the excitation wavelength of 400nm, exhibited characteristic emission peaks for Sm3+ at 560, 597, and 643nm. The purely magnetic dipole allowed transition ((4)G(5/2)(6)H(5/2)) at 560nm and partly magnetic dipole transition ((4)G(5/2) H-6(7/2)) at 597nm, responsible for orange-red light, dominated the emission spectra. In contrast to the magnetic dipole transitions, the electric dipole transition ((4)G(5/2)(6)H(9/2)) was found to be relatively less intense confirming high symmetrical crystal environment around Sm3+ in the host lattice. However, with subsequent substitution of Gd3+ at the lanthanide site in the host lattice, the crystal field suffered distortion and thus, influenced the photometric properties. From experimental results, it was evident that these phosphors have suitable Commission International de l'Eclairage (CIE), color correlated temperature (CCT) parameters, appreciable lifetime, and excellent color purity with respect to other reported rare earth ion doped orange-red phosphors. Further, these results could help in the improvisation of their use in optoelectronics especially white LEDs, photovoltaic cells and other strategic applications

Effect of Ca2+ ion co-doping on radiative properties via tuning the local symmetry around the Eu3+ ions in orange red light emitting GdPO4:Eu3+ phosphors

A series of Ca2+ substituted GdPO4:Eu3+ novel phosphors were prepared via the solid state method. Rietveld refinement of the XRD data and transmission electron microscopy results confirmed that all these compounds adopted the monazite phase with space group P21/n. Fourier transform infrared spectroscopy (FTIR) analysis confirmed the presence of the characteristic vibrational bands for host matrix of GdPO4, and field emission scanning electron microscopy (FESEM) results revealed that the particles possess agglomerated granular morphology. Photo-luminescent spectra displayed the representative luminescence D-5(0) F-7(J) (J = 0-4) intra-4f shell Eu3+ ion transitions. The magnetic dipole (D-5(0) F-7(1)) transition was stronger than the electric dipole (D-5(0) F-7(2)) transition. On co-doping Ca2+ content to Gd0.93Eu0.07PO4 phosphor, we observed the enhanced PL intensity as a function of Ca2+ content; the maximum intensity of 1.5 times was observed for 7 mol% of calcium doped Gd0.93Eu0.07PO4 phosphor. The enhancement of the PL intensity owing to the effective ionic radius and the mismatch in Pauling's electronegativity between co-dopant and host cations causes distortion of local crystal field surrounding the Eu3+ ions. Furthermore, this local distortion or reduced symmetry effect around the Eu3+ ions was reconfirmed by the Judd-Ofelt and life time decay analyses. The evaluated 1931 Commission International de l'Eclairage (CIE) chromaticity color coordinates exhibit orange red emission (x = 0.6247, y = 0.3748) with minimal CCT values and high color purity. This class of phosphors possessed excellent thermal stability at high temperature, and the integrated emission intensity at 423 K was about 66% of that at 303 K. Considering the above results, the Eu3+/Ca2+ co-doped GdPO4 phosphors have potential applications in the near-UV excited white light emitting diodes

Synthesis and structural characterization of orange red light emitting Sm3+ activated BiOCl phosphor for WLEDs applications

We report, synthesis of orange red light emitting Sm3+ activated BiOCl phosphors at relatively low temperature (400 degrees C) and shorter duration of 1 h. Rietveld refined results confirmed that all the compounds crystallized in the tetragonal structure with space group P4/nmm (No. 129). Functional group analysis were carried out by Fourier transform infrared (FT-IR) and Raman spectroscopy. The Photoluminescent (PL) experiment results reveal that, an intense PL transition at 598 nm ((4)G(5/2) -> H-6(7/2)) corresponds to orange red emission at lambda(ex) = 408 nm. The maximum emission intensity was observed for BiOCl: Sm3+ (3 mol%) phosphor, above this concentration quenching takes place due to charge exchange with neighboring Sm3+ ions. Time resolved fluorescence spectroscopic result reveals that, the decay curve is bi-exponential in nature and having long lifetime (tau = 0.58 ms). The obtained CIE and CCT values suggest that these phosphors having excellent color purity (similar to 90%) and low correlated color temperature. These results suggest that, Sm3+ activated BiOCl can be a potential red phosphor materials for WLEDs and other optoelectronics applications. (C) 2019 Elsevier B.V. All rights reserved

Synthesis, Structure and Photoluminescence Properties of Sm3+-doped BiOBr Phosphor

Well-crystallized tetragonal layered BiOBr and Bi0.95Sm0.05OBr phosphors were prepared by the solid state method. These compounds were characterized using powder X-Ray diffraction and photoluminescence technique. In PL spectra, the electric dipole transitions dominate than other transitions which indicate that the Sm3+ ions occupy a site with an inversion center of BiOBr. CIE chromaticity diagram confirmed that these phosphors can be useful in the fabrication of red component in white light emitting diodes (WLEDs) for display device applications

Alkali metal ion co-doped Eu3+ activated GdPO4 phosphors: Structure and photoluminescence properties

Series of alkali metal ion co-doped with Eu3+ activated GdPO4 phosphors were synthesized by the conventional solid state method. Structural parameters were confirmed by the X-ray Rietveld refinement method. All the compounds are crystallized in the monazite phase with space group (P121/n1, No.14). Morphology and functional group analysis were performed on scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Room temperature photoluminescence (PL) spectroscopic results reveal that, on Eu3+ ion doping in the GdPO4 host matrix, the magnetic dipole transition (5D0 → 7F1) at 581 nm responsible for orange light, dominates the red emission with respect to the electric dipole transition (5D0 → 7F2) at 620 nm. It was found that the emission intensity increased up to 9 mol% of Eu3+ and then quenched due to multipolar interactions. Further, co-doping with Li+, Na+ and K+ ion in to Eu3+ activated GdPO4 phosphor led to an enhancement in luminescence intensity by reducing the parity restriction of electric dipole transitions as a consequence of suitable local distortion of the crystal field surrounding the Eu3+ activator ion. The results of Judd–Ofelt theory and radiative parameters suggest that these phosphors have a short lifetime, good quantum efficiency, excellent color purity compared to other reported Eu3+ doped phosphors. These results illustrate the mechanistic effect of alkali metal ions doping on luminescent properties of rare earth ion doped GdPO4 phosphors and help in optimization of their luminescent properties according to the practical requirements in optoelectronic and biomedical applications

Blue emitting Ce3+ -doped CaYAl3O7 phosphors prepared by combustion route

The solution-combustion route was used to synthesize series of Ce3+-ion-activated CaYAl3O7 (CYO) blue-light-emitting phosphors. Formation of the tetragonal CYO structure was confirmed by the powder X-ray diffraction (XRD) studies. On substitution of Ce3+ ion to Ca site in CaYAl3O7 system, the photoluminescence spectra recorded at ultraviolet-light (360 nm) excitation. Photoluminescence excitation spectra at 360 nm showed the characteristic emission at 434 nm of the Ce3+ ion caused by 5d -> 4f transitions. Increase in intensity can be seen up to 1 mol % of Ce3+ followed by quenching due to dipole-dipole interaction. The Commission Internationale de l'Eclairage (CIE - 1931) coordinates x = 0.1484 and y = 0.0987 of this phosphor are in the violet blue region. The blue-color purity was found to be maximum 90% for 1 mol% Ce3+-doped phosphor. The obtained CIE, CCT, and color-purity results illustrate the potentiality of Ce3+ activated CYO phosphor for household-lighting and display-device applications