Upadhyayula V Varadaraju

A series of orange-red emitting phosphor compositions Sr1.9-x Bax Eu0.05 Li0.05 MoO6 (x=0-1.9) have been synthesized and characterized by powder X-ray diffraction (XRD) and photoluminescence. XRD results reveal a phase transition from orthorhombic to pseudocubic structure for x0.2. All the compositions show broad charge-transfer band absorption in the near-ultraviolet (UV) region. Orange-red emission is observed for compositions with lower x values (x0.6), whereas orange emission is observed for compositions with higher x values. Select compositions in this system of compounds could find potential applications as orange-red phosphors for white light generation using near-UV/blue GaN -based light emitting diodes. © 2006 The Electrochemical Society.

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.

Intense red phosphors, AgGd0.95Eu0.05(WO 4)2-x(MoO4)x (x = 0-2) have been synthesized and characterized by powder X-ray diffraction (XRD) and photoluminescence. Powder XRD results reveal a phase transition from monoclinic to tetragonal structure at x ≥ 0.5. All compositions with Eu3+ show red emission on excitation either in the charge-transfer band or Eu3+ levels. Intense red emission is obtained in the molybdates, AgGd0.95Eu 0.05(MoO4)2 under 465-nm excitation. Studies on AgGd1-yEuy(WO4)2 and AgGd 1-yEuy(WO4)2 (y = 0.1 - 1 in steps of 0. 1) show that the emission intensity is maximum for compositions with y = 0.2 and 0.3, respectively, and a decrease in emission intensity is observed for higher y values. The intense red emission of the tungstate and molybdate phosphors under 394 and 465 nm excitation, respectively, suggests that these materials are promising candidates as red-emitting phosphors for near-UV/blue GaN-based light-emitting diodes for white light generation. © 2005 The Electrochemical Society. All rights reserved.

Eu2+ luminescence is studied in Sr2 LiSiO4 F, and the emission spectrum shows an intense and broad green emission band with two peak maxima (475 and 505 nm). The two emission bands are due to Eu2+ present in the two crystallographic distinct Sr sites in the host lattice. Ce3+ luminescence is studied in Sr2 LiSiO4 F and shows a broad and bright blue emission band at around 430 nm under 350 nm excitation. The effect of Ce3+ co-doping is studied in Sr2 LiSiO4 F: Eu2+ phosphor. Thus, the co-doping of Ce3+ also enhances the absorption of Eu2+ in the near-UV region, where the light-emitting diode emission occurs. Ce3+ co-doped samples show broad-band emission ranging from 360 to 620 nm (blue to green-yellow), which results in white emission. This indicates partial energy transfer from Ce3+ to Eu2+. Selected compositions of this phosphor material can find potential application in solid-state lighting. © 2009 The Electrochemical Society.

Rare earth based materials have recently attracted considerable attention as potential eco-friendly colourants for low temperature as well as high temperature applications. In the present study, we have synthesized a series of Ca-doped PrPO4 compounds with the general formula, Pr 1-xCaxPO4 (x = 0-0-4 in steps of 0-1) and characterized the compounds by powder X-ray diffraction. All the compositions show a monoclinic monazite structure. The optical properties of the brilliantly coloured pigments [L (brightness), a* (+ red - green), b* (+ yellow - blue)] have been examined. These materials can find application as potential green colourants. © Indian Academy of Sciences.

Investigation of photoluminescence of Eu3+ -doped double perovskites with the formula A2 CaMo O6 (A=Sr, Ba) revealed that the electric dipole transition is present when Eu3+ is doped at the noncentrosymmetric Sr site vis-a-vis substitution at the centrosymmetric Ca site. Strong CT band absorption was observed in both series of compounds in the near ultraviolet region. Commission Internationale de I'Eclairage chromaticity coordinates indicate that Eu3+ -doped Sr2 CaMo O6 compounds are potential orange-red emitting phosphors, whose emission intensity is 1.5 times that of commercial Y2 O2 S:Eu phosphor for white LEDs based on NUV GaN based LEDs. © 2006 The Electrochemical Society.

Ce3+ luminescence is studied for the first time in BaMgSiO4. Intense and broad blue emission is observed with maximum at 430 nm when excited with 356 nm. Studies on Ba1-2y Cey Liy MgSiO4 (y=0.0025-0.125) show that the emission intensity is maximum for y=0.1 and a decrease in emission intensity is observed for higher y values. The concentration of Eu2+ and Ce3+ are varied in BaMgSiO4: 0.1 Ce3+, Eu2+, and BaMgSiO4: 0.01 Eu2+, Ce3+ systems, respectively, in order to find the critical concentration of Eu2+ and Ce3+ to achieve high emission intensity of Eu2+. Ba0.75 Eu0.05 Ce0.1 Li0.1 MgSiO4 and Ba0.97 Eu0.01 Ce0.01 Li0.01 MgSiO4 compositions show maximum Eu2+ emission, and the emission intensity is found to be comparable with that of commercial ZnS:Cu,Al (green phosphor, SONY) under near-UV excitation (400 nm). Commission Internationale de I'Eclairage (CIE) chromaticity coordinates indicate that the Eu2+ and Ce3+ substituted compositions are potential green phosphors for solid-state lighting, light-emitting diode technology. © 2007 The Electrochemical Society.

A series of novel red-emitting phosphors Ag La0.95 Eu0.05 (W O4) 2-x (Mo O4) x [x=0-2] have been synthesized and their luminescence properties investigated. All Eu3+ activated compositions show red emission on excitation either in the charge-transfer band or Eu3+ levels. All compositions show remarkably intense red emission with excitation at 465 nm. The photoluminescence studies on Ag La1-y Euy (W O4) 2 and Ag La1-y Euy (Mo O4) 2 (y=0.1-1 in steps of 0.1) show that the emission intensity is maximum for compositions with y=0.4 and 0.3, respectively, and a decrease in emission intensity is observed for compositions with higher y values. Select compositions in this system of compounds could find potential application as red phosphors for white-light generation using blue GaN-based light-emitting diodes (LEDs). © 2006 The Electrochemical Society. All rights reserved.