Synthesis, phase transition and photoluminescence studies on Eu3+-substituted double perovskites-A novel orange-red phosphor for solid-state lighting
Photoluminescence studies on Eu3+-doped double perovskites with the formula A2CaWO6 (A=Sr, Ba) revealed that the forced electric dipole (ED) transition is present when Eu3+ is substituted at the non-centrosymmetric Sr-site vis-a-vis substitution at the centrosymmetric Ca-site shows both ED and magnetic dipole (MD) transition. A series of novel orange-red-emitting phosphor compositions Sr1.9-xBaxEu0.05Li0.05CaWO6 (x=0-1.9) have also been synthesized and characterized by powder X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS) and photoluminescence. XRD results reveal a phase transition from monoclinic to pseudo-cubic structure for x≤0.2. All the compositions show broad charge transfer band and orange-red (MD and ED) emission. However, the relative intensity of the MD and ED depends on the Ba content present in the host lattice. Select compositions in this system of compounds could find potential application as orange-red phosphors for white light generation using blue/near-UV GaN-based light-emitting diodes (LEDs). © 2008 Elsevier Inc. All rights reserved.
Synthesis and Eu3+ luminescence in new oxysilicates, ALa 3Bi(SiO4)3O and ALa2Bi 2(SiO4)3O [A=Ca, Sr and Ba] with apatite-related structure
New oxysilicates with the general formula ALa3Bi(SiO 4)3O and ALa2Bi2(SiO 4)3O [ACa, Sr and Ba] are synthesized and characterized. Powder X-ray diffraction of these silicates show that they are isostructural with BiCa4(VO4)3O which has an apatite-related structure. Eu3+ luminescence in the newly synthesized oxysilicates show broad emission lines due to disorder of cations. The relatively high intense magnetic dipole transition 5D0→ 7F1 points to a more symmetric environment. The photoluminescence results confirm that the compounds have apatite-related crystal structure. © 2005 Elsevier Inc. All rights reserved.
Role of crystallite size on the photoluminescence properties of SrIn2O4:Eu3+ phosphor synthesized by different methods
Photoluminescence (PL) of Eu3+ was studied in SrIn2O4 host lattice. A complete solid solubility of Eu3+ has been found in the series SrIn2-xEuxO4 [x=0-2.0]. The phase formation at a relatively low temperature and in a very short duration was achieved by combustion synthesis (CS). Concentration quenching of luminescence has been observed in SrIn2-xEuxO4 [x=0.1-2.0] and the critical concentration for maximum emission was found to be with x=0.3. In order to find the role of crystallite size on the PL properties of SrIn2O4:Eu3+, the results obtained with phosphors synthesized by solid state reaction (SSR) and CS methods were compared. © 2008 Elsevier Inc. All rights reserved.
Host-sensitized emission of LiInW2O8 wolframites: From red-Eu3 to white-Dy3 phosphors
The LiInW2O8:Eu3, LiInW2O 8:Dy3 and LiInW2O8:Eu 3/Dy3 phosphors were synthesized by solid-state reaction and their photoluminescence properties were studied. Under UV excitation, the LiInW2O8:Eu3 phosphor exhibits an intense red emission whereas the LiInW2O8:Dy3 and LiInW2O8:Dy3/Eu3 phosphors show a white emission. The WO6 octahedra play a major role in the luminescence of the host lattice, characterized by a blue emission under UV excitation. The emission of activator ion results from an efficient energy transfer from the LiInW2O8 host lattice to the Eu 3 and Dy3 ions. The LiIn0.97Dy30.03W2O8 and LiIn0.965 Dy 30.03Eu30.005W2O 8 samples, optimized for white emission, are interesting candidates for solid-state lighting applications. © 2011 Elsevier Inc.
Eu3+ luminescence in La5Si2BO13 with apatite related structure and magnetic studies in Ln5Si 2BO13 (Ln=Gd, Dy)
Eu3 photoluminescence is studied in La5Si 2BO13 with apatite related structure. La 5-xEuxSi2BO13 [x=0.05, 0.1, 0.3, 0.5, 0.7, 1.0, 2.0] compositions are synthesized. The emission results shows that Eu3 ions occupy two different cationic sites viz., La(1) and La(2). The increase in the intensity of 5D07F0 line with increasing Eu3 content shows the preferential occupancy of Eu3 in La(2) site due to the existence of short La(2)O(4) (free oxide ion) bond. The observation of antiferromagnetic interactions in Gd and Dy analogues supports the structural features elucidates from photoluminescence studies. © 2010 Published by Elsevier Inc.
Li3Gd3Te2O12:Eu3+- an intense red phosphor for solid state lighting applications
Li3Gd3−3xEu3xTe2O12 (x=0.05−1.0) phases with garnet structure were synthesized by high temperature solid state reaction and the photoluminescence properties were investigated. The appearance of bands due to intra 4 f transitions of Gd3+ in the excitation spectra recorded by monitoring the 612 nm emission line of the activator indicates Gd3+→Eu3+ energy transfer in this host lattice. Under 395 nm excitation, the electric dipole transition is predominant in the emission spectrum of Eu3+ and is in agreement with the C2 point group (noncentrosymmetric) of the EuO8 polyhedron. The critical concentration of the Eu3+ activator in this series was found to be 0.6 (x=0.2) above which, concentration quenching occurs. The emission intensity of the phosphor composition, Li3Gd2.4Eu0.6Te2O12 is ~4 times that of the commercial sample of Y2O3:Eu3+ phosphor.
Intense Photoluminescence Emission in Eu3+- and Dy3+- Doped Low-Band Gap Perovskite Titanate, Na0.5Gd0.5TiO3
Na0.5Gd0.5-xRExTiO3 (RE=Eu and Dy) phases with orthorhombic perovskite structure were synthesized by high temperature solid state reaction and the photoluminescence properties were investigated. The phase purity was confirmed by Rietveld refinement of the powder XRD patterns in Pnma space group. The band gap of the host was found to be 3.41 eV from UV/Vis diffuse reflectance spectrum. In the Eu3+ doped phases, the 5D0→7F2 electric dipole (ED) transition is predominant in the emission spectrum of Eu3+, under 397 nm excitation, and is in agreement with the non-centrosymmetric Cs point group of the EuO8 polyhedron. The critical concentration of the Eu3+ was found to be x=0.075 above which, concentration quenching occurs. Dy3+ doping resulted in intense white light emission under 389 nm excitation.
Eu 3+ Photoluminescence in LiGd(WO 4 ) 2 with Scheelite-Related Structure
A comparative study of Eu 3+ photoluminescence in the Scheelite-type oxides LiGd(WO 4 ) 2 and LiGd(MoO 4 ) 2 is made. From the emission results, it is observed that the 5 D 0 → 7 F 2 electric dipole transition at 615 nm is predominant in both cases. The critical concentration of Eu 3+ is found to be x=0.3 in both LiGd 1-x Eu x (WO 4 ) 2 as well as LiGd 1-x Eu x (MoO 4 ) 2 . The emission intensity of Eu 3+ is higher in the tungstate host lattice vis a vis the molybdate. In addition, the emission intensity of Eu 3+ in LiGd 0.7 Eu 0.3 (WO 4 ) 2 is 3.3 times higher compared to that of Y 2 O 3 :0.05Eu 3+ commercial red phosphor.
Photoluminescence properties of rare earths (Eu 3, Tb 3, Dy 3 and Tm 3) activated NaInW 2O 8 wolframite host lattice
The photoluminescence (PL) studies on NaIn 1-xRE xW 2O 8, with RE=Eu 3, Tb 3, Dy 3 and Tm 3 phases have shown that the relative contribution of the host lattice and of the intra-ff emission of the activators to the PL varies with the nature of the rare earth cation. In the case of Dy 3 and Tm 3 activators, with yellow and blue emission, respectively, the energy transfer from host to the activator plays a major role. In contrast for Eu 3, with intense red emission, the host absorption is less pronounced and the intra-ff transitions of the Eu 3 ions play a major role, whereas for Tb 3 intra-ff transitions are only observed, giving rise to green emission. © 2011 Elsevier Inc. All rights reserved.