Srinivasa Buddhudu

Luminescence of Eu3+ and Tb3+ doped Zn2SiO4 nanometer powder phosphors

Abstract We report, for the first time to the best of our knowledge, the luminescent properties of Tb 3+ and Eu 3+ doped Zn 2 SiO 4 phosphors prepared by a sol–gel process. The phosphors have shown prominent luminescence in green and red, respectively, due to the electronic transitions of 5 D 0 → 7 F 2 (Eu 3+ ) and 5 D 4 → 7 F 5 (Tb 3+ ). Structural characterization of these luminescent materials was carried out with XRD and TEM. Luminescence spectra were analyzed by measuring the excitation, photoluminescence spectra and lifetimes of the emission transitions of Eu 3+ ( 5 D 0 → 7 F J , J =1–5) and Tb 3+ ( 5 D 4 → 7 F J , J =1–6). Our experimental results have shown that these phosphors have comparable luminescence properties as those currently used in TVs and CRTs.

Photoluminescence of ZnS:Mn embedded in three-dimensional photonic crystals of submicron polymer spheres

ZnS:Mn has been in-filled in photonic crystals of submicron polymer spheres. The effect of the photonic band gap on the photoluminescence (PL) properties of ZnS:Mn has been investigated. Because of the overlap of the transmission dip of the photonic crystal and the photoluminescence band of ZnS:Mn, both suppression and enhancement in the PL of the phosphor have been observed. A strong dependence of the fluorescence lifetime on the emission wavelength in the range of the stop band has been found. This strong dependence is believed to arise from the very low photon density of state within the stop band of the ZnS:Mn in-filled photonic crystal as result of a high dielectric contrast between ZnS:Mn and the polystyrene spheres.

980nm laser-diode-excited intense blue upconversion in Tm3+∕Yb3+-codoped gallate–bismuth–lead glasses

Intense blue-upconversion in Tm3+∕Yb3+-codoped gallate–bismuth–lead glasses has been achieved under an excitation from a commercially available 980nm laser diode. Energy transfer processes and excited-state absorption account for the population of the G41 emitting level of the Tm3+. Although the addition of GeO2 has enhanced the glass thermal stability, the phonon mode associated with vibration of GeO2 has almost no influence on the blue-upconversion intensity and the radiative lifetime of H43 level. The dependence of the phonon energy of the host on contributions from multiphonon decay on the fluorescence has been discussed. Significant enhancement of the blue-upconversion has also been observed in gallate–bismuth–lead glasses with the incorporation of PbF2 content.Intense blue-upconversion in Tm3+∕Yb3+-codoped gallate–bismuth–lead glasses has been achieved under an excitation from a commercially available 980nm laser diode. Energy transfer processes and excited-state absorption account for the population of the G41 emitting level of the Tm3+. Although the addition of GeO2 has enhanced the glass thermal stability, the phonon mode associated with vibration of GeO2 has almost no influence on the blue-upconversion intensity and the radiative lifetime of H43 level. The dependence of the phonon energy of the host on contributions from multiphonon decay on the fluorescence has been discussed. Significant enhancement of the blue-upconversion has also been observed in gallate–bismuth–lead glasses with the incorporation of PbF2 content.

Green upconversion luminescence in Er3+:BaTiO3 films

Green upconversion emissions at 548 and 528 nm have been obtained from sol-gel derived nanocrystalline Er3+:BaTiO3 films under 980 nm excitation. The green emissions are attributed to the ground-state (4I15/2) -directed transitions from 2H11/2 (528 nm) and 4S3/2 (548 nm) of Er3+ ions. Analysis of the temporal evolution of the emission at 548 nm shows that both excited state absorption of individual ion and energy transfer between the two neighboring ions contribute to the upconversion emissions in Er3+ (3 mol %):BaTiO3 film. The lifetime of the dominant emission at 548 nm is about 90 μs.

Luminescent properties of rare-earth ion doped yttrium silicate thin film phosphors for a full-colour display

In this paper, we report our results on the sol–gel preparation and spectral properties of (RExY1−x)2SiO5 (RE3+ = Eu3+, Tb3+, Ce3+, x = 0.005, 0.01, 0.02, 0.03 and 0.05) thin films. Effects of annealing temperatures on the thin films structure and optical properties, including luminescence, decay kinetics and CIE colour coordinates have been investigated. Upon exposure to the UV source, films containing Eu3+ and Tb3+ have exhibited bright red- and green-phosphorescent colours, due to the prominent transitions of 5D0→7F2 at 613 nm of Eu3+ and 5D4→7F5 at 543 nm of Tb3+ arising because of the intra-4f n electronic transitions, respectively. The photoluminescence spectrum of (CexY1−x)2SiO5 film mainly shows a broader emission band at 488 nm, which originates from the 5d→4f electron transitions of Ce3+. Luminescence mechanisms of these phosphor thin films have been discussed in detail.

Emission properties of GdOBr: Ce3+ and Tb3+ phosphors

Abstract The present investigation aims to elucidate the photoluminescent behavior of luminescent powder phosphors of GdOBr:Ce 3+ and GeOBr:Tb 3+ prepared by a solid state reaction method. Their emission properties have been systematically investigated. Photoluminescence have revealed a bright and broader (320–480 nm) violet-blue color emission (FWHM=85 nm) from the Ce 3+ (5d( 2 D)→ 2 F 5/2 ) and an intense and sharp (543 nm) green color emission (FWHM=5 nm) from Tb 3+ ( 5 D 4 → 7 F 5 ) phosphors as well as three other weaker emission transitions 5 D 4 → 7 F 6, 4, 3 at 485, 582 and 619 nm. Under a UV source, a very bright green emission color has been observed from terbium phosphor and a strong bluish violet color from cerium phosphor. The emission color richness defining CIE coordinates have been evaluated for these blue-violet ( x =0.155, y =0.008) and green ( x =0.285, y =0.554) luminescent powder phosphors.

Enhancement of green emission from Tb3+:GdOBr phosphors with Ce3+ ion co-doping

Abstract A strong green emission (5D4→7F5) has been observed from Tb3+ (1.0 mol%) doped into GdOBr powder phosphors upon excitation with an UV-wavelength (226 nm). To this phosphor, different amounts of Ce3+ (from 0.1 to 1.5 mol%) have been added to further improve the green emission efficiency of Tb3+-doped GdOBr. It has been found that the optimum concentration, 0.2 mol% of Ce3+, results in a twofold enhancement of the green emission intensity. The green emission from Tb3+ could not be increased at higher Ce3+ concentrations due to the Ce3+-Ce3+ ion interactions, i.e., the concentration quenching effect. The mechanism involved in the energy transfer between the Ce3+ and Tb3+ has been explained with an energy level diagram.

Visible up-conversion luminescence in Er3+:BaTiO3 nanocrystals

Abstract Visible emissions at 548, 528 and 660 nm have been observed from the sol–gel derived nanocrystalline Er 3+ :BaTiO 3 powders under infrared excitations at both 980 and 810 nm. Combined with the energy level structure of Er 3+ and the decay kinetics of the green emissions, the up-conversion mechanism has been analyzed and explained. The bright green emission at 548 nm has been attributed to the ground state-directed transition from 4 S 3/2 , which is populated through excited state absorption (ESA) for 810 nm excitation, and through both ESA and energy transfer (ET) processes for 980 nm excitation.

Deposition and photoluminescence of sol-gel derived Tb3+:Zn2SiO4 films on SiO2/Si

Abstract Tb3+ doped Zn2SiO4 films have been deposited on SiO2 buffered Si wafers by sol–gel method. The structures of these films have been investigated with X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The results revealed that these films were composed of nanometer-size grains with a Willemite structure and had smooth surfaces. Photoluminescence measurements of the films showed a strong emission from 5D4 to 7F5 at 544 nm. The blue emission from 5D3–7Fj was depressed because of cross-relaxation effect. The decay kinetics of the 5D4–7F5 green emission was studied and a best fitting was obtained by a double exponential function. The lifetime of the excited 5D4 state is estimated to be 5.2 ms.

Photoluminescence of CdSe nanocrystallites embedded in BaTiO3 matrix

This letter reports the photoluminescence properties of CdSe quantum dots (QDs) embedded in a ferroelectric BaTiO3 matrix. The main emission from the samples has been assigned to the band–edge transition of QDs. With an increase in the heat treatment temperature, the emission peak has been shifted to a longer wavelength. This shift has been attributed due to the dielectric environment effects of the matrix on the electronic structure of the QDs. The dependences of the peak position on the heat-treatment temperature and dot size are found in agreement with the theoretical simulation results reported previously.