Microspherical, hierarchical structures of blue-green-emitting Dy:GdOOH and Dy:Gd2O3

Dy-doped GdOOH microspherical structures were prepared in minutes without using any structure-directing agents, through the microwave irradiation route. The as-prepared product consists of nearly monodisperse sphere-like entities with each one representing a three-level hierarchy in its formation. Dy:GdOOH powder samples show a bright blue-green luminescence under UV excitation, making these structures potentially important in the field of optical and luminescent devices. Finally, thermal conversion to the corresponding oxide structures occurs at modest temperatures, spherical morphology intact and with enhanced luminescence behaviour. (C) 2014 Elsevier B.V. All rights reserved.

Luminescence studies and EPR investigation of derived Eu doped ZnO

ZnO:Eu (0.1 mol%) nanopowders have been synthesized by auto ignition based low temperature solution combustion method. Powder X-ray diffraction (PXRD) patterns confirm the nanosized particles which exhibit hexagonal wurtzite structure. The crystallite size estimated from Scherrer's formula was found to be in the range 35-39 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies reveal particles are agglomerated with quasi-hexagonal morphology. A blue shift of absorption edge with increase in band gap is observed for Eu doped ZnO samples. Upon 254 nm excitation, ZnO:Eu nanopowders show peaks in regions blue (420-484 nm), green (528 nm) and red (600 nm) which corresponds to both Eu2+ and Eu3+ ions. The electron paramagnetic resonance (EPR) spectrum exhibits a broad resonance signal at g= 4.195 which is attributed to Eu2+ ions. Further, EPR and thermo-luminescence (TL) studies reveal presence of native defects in this phosphor. Using TL glow peaks the trap parameters have been evaluated and discussed. (C) 2014 Elsevier B.V. All rights reserved.

Luminescence enhancement in monoclinic CaAl2O4:Eu2+, Cr3+ nanophosphor by fuel-blend combustion synthesis

Eu2+ ion doped into a suitable host results in an efficient luminophore with engineering relevance; however stabilizing this ion in a host is known to be a challenge. Here we report a novel approach for the synthesis of efficient CaAl2O4 phosphor containing Eu2+ luminophore and Cr3+ activator. CaAl2O4:Eu2+, Cr3+ is prepared by a solution combustion (SCS) method using (i) urea, (ii) oxalyl dihydrazide (ODH) and (iii) fuel-blend (in which overall fuel to oxidizer ratio (F/O) = 1). A Multi-channel thermocouple setup is used to measure the flame temperatures to study the nature of combustion of various fuel mixtures. The variation of adiabatic flame temperature is calculated theoretically for different urea/ODH mixture ratios according to thermodynamic concept and correlated with the observed flame temperatures. Blue emission of the CaAl2O4:Eu2+ phosphor is enhanced similar to 20 times using the fuel-blend approach. Using the observed reaction kinetics, and the known chemistry of smoldering type combustion, a mechanism is proposed for the observed stabilization of Eu2+ ion in the fuel-blend case. This also explains the observed improvement in blue light emission. We show that the right choice of the fuel ratio is essential for enhancing photoluminescence (PL) emission. The PL intensity is highest for ODH lean and urea rich combination (i.e. when the ratio of ODH:urea is 1:5); measured color purity is comparable to commercial blue phosphor, BAM:Eu2+. (C) 2015 Elsevier B.V. All rights reserved.

Spectral characterizations and photophysical properties of one-step synthesized blue fluorescent 4 `-aryl substituted 2,2 `:6 `,2 `'-terpyridine for OLEDs application

We have synthesized a series of 4'-aryl substituted 2,2':6',2 `'-terpyridine (terpy) derivatives, namely 4'-(4-methylphenyl)-2,2':6',2 `'-terpyridine (C-1), 4'-(2-furyl)-2,2':6'2 `'-terpyridine (C-2), and 4'-(3,4,5-trimethoxyphenyl)-2,2':6',2 `'-terpyridine (C-3). The synthesized terpy compounds were characterized by elemental analyses, FTIR, NMR (H-1 and C-13), and ESI-Mass spectrometry. Photophysical, electrochemical and thermal properties of terpy compounds were systematically studied. Maximum excitation band was observed between 240 and 330 nm using UV-visible spectra, and maximum emission peaks from PL spectra were observed at 385, 405 and 440 nm for C-1, C-2 and C-3 respectively. Fluorescence lifetime (tau) of the fluorophores was found to be 035 and 1.55 ns at the excitation wavelength of 406 nm for C-1 and C-2 respectively, and tau value for C-3 was found to be 0.29 ns at the excitation wavelength of 468 nm. We noticed that the calculated values of HOMO energy levels were increased from 5.96 (C-1) to 6.08 (C-3) eV, which confirms that C-3 derivative is more electrons donating in nature. The calculated electrochemical band gaps were 2.95, 2.82 and 3.02 eV for C-1, C-2 and C-3 respectively. These blue fluorescent emitter derivatives can be used as an electron transport and electroluminescent material to design the blue fluorescent organic light emitting diode (OLED) applications. (C) 2015 Elsevier B.V: All rights reserved.

Boron-doped carbon nanoparticles: Size-independent color tunability from red to blue and bioimaging applications

Here, we report the hydrothermal synthesis of boron-doped CNPs (B-CNPs) with different size/atomic percentage of doping and size-independent color tunability from red to blue. The variation of size/atomic percentage of B is achieved by simply varying the reaction time, while the color tunability is obtained by diluting the solution. With dilution, the luminescence spectra are not only blue-shifted, the intensity increases as well. The huge blue-shift in the emission energy (similar to 1 eV) is believed to be due to the increase in the interparticle distance. The quantum yield with optimum dilution is found to increase with boron doping though it is very low as compared to CNPs and nitrogen-doped CNPs. Finally, we show that B-CNPs with a quantum yield of 0.5% can be used for bioimaging applications. (C) 2015 Elsevier Ltd. All rights reserved.

Yellow-red luminescence in ZnO nanoparticles synthesized from zinc acetylacetonate phenanthroline

ZnO powders/thin films/coatings when excited by a suitable excitation source, usually yield green luminescence in the visible wavelength range along with characteristic ultra-violet emission. We report yellow-red emission from ZnO nanoparticles synthesized within 5 min of microwave irradiation by using zinc acetylacetonate phenanthroline as the starting precursor material. The emission is strongly dependent on the typical structure of the starting precursor for ZnO synthesis, where one phenanthroline moiety is attached with zinc acetylacetonate hydrate complex. These ZnO nanoparticles could be potentially suitable phosphor for white light generation when excited by a blue laser. In contrast, the ZnO nanoparticles obtained from zinc acetylacetonate by similar method yield weak green emission. (C) 2015 Elsevier B.V. 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.

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.

Transparent Ni2+-doped ZnO-Al2O3-SiO2 system glass-ceramics with broadband infrared luminescence

We report transparent Ni2+-doped ZnO-Al2O3-SiO2 system glass-ceramics with broadband infrared luminescence. After heat-treatment, ZnAl2O4 crystallite was precipitated in the glasses, and its average size increased with increasing heat-treatment temperature. No infrared emission was detected in the as-prepared glass samples, while broadband infrared luminescence centered at 1310 nm with full width at half maximum (FWHM) of about 300 nm was observed from the glass-ceramics. The peak position of the infrared luminescence showed a blue-shift with increasing heat-treatment temperature, but a red-shift with an increase in NiO concentration. The mechanisms of the observed phenomena were discussed. These glass-ceramics are promising as materials for super broadband optical amplifier and tunable laser. (c) 2006 Elsevier Ltd. All rights reserved.

Intense greeen upconversion luminescence in Er3+: Yb3+ codoped fluorophosphate glass ceramic containing SrTe5O11 nanocrystals

Er3+:Yb3+ codoped tellurite-fluorophosphate (TFP) glass ceramic exhibits much stronger upconversion luminescence. The intensity of the 540 nm green light and 651 nm red light of the TFP glass ceramic is 120 times and 44 times stronger than that of the fluorophospahte (FP) glass, respectively. XRD analysis shows that the nanocrystal in TFP glass ceramic is SrTe5O11. TFP glass ceramic also displays much higher upconversion fluorescence lifetime and crystallization stability. The narrow and strong peak at 540 nm is very ideal for practical upconversion luminescence realization. This work is a new trial for exploring non-PbF2 involved nanocrystal upconversion glass ceramics.

Intense frequency upconversion luminescence in Yb3+/Tm3+-codoped oxychloride germanate glasses

Yb3+/Tm3+-codoped oxychloride germanate glasses for developing potential upconversion lasers have been fabricated and characterized. Structural properties were obtained based on the Raman spectra analysis, indicating that PbCl2 plays an important role in the formation of glass network and has an important influence on the maximum phonon energies of host glasses. Intense blue and weak red emissions centered at 477 and 650 nm, corresponding to the transitions (1)G(4) -> H-3(6) and (1)G(4) -> H-3(4), respectively, were observed at room temperature. With increasing PbCl2 content, the intensity of blue (477 nm) emission increases significantly, while the red (650 nm) emission increases slowly. The results indicate that PbCl2 has more influence on the blue emissions than the red emission in oxychloride germanate glasses. The possible upconversion mechanisms are discussed and estimated. Intense blue upconversion luminescence indicates that these oxychloride germanate glasses can be used as potential host material for upconversion lasers. C (c) 2005 Springer Science + Business Media, Inc.

Energy transfer and infrared-to-visible upconversion luminescence of Er3+/Yb3+-codoped halide modified tellurite glasses

We report on the energy transfer and frequency upconversion spectroscopic properties of Er3+-doped and Er3+/Yb3+-codoped TeO2-ZnO-Na2O-PbCl2 halide modified tellurite glasses upon excitation with 808 and 978 nm laser diode. Three intense emissions centered at around 529, 546 and 657 nm, alongwith a very weak blue emission at 4 10 nm have clearly been observed for the Er3+/Yb3+-codoped halide modified tellurite glasses upon excitation at 978 nm and the involved mechanisms are explained. The quadratic dependence of fluorescence on excitation laser power confirms the fact that the two-photon contribute to the infrared to green-red upconversion emissions. And the blue upconversion at 410 nm involved a sequential three-photon absorption process. (c) 2005 Elsevier Ltd. All rights reserved.

Upconversion luminescence of Tm3+/Yb3+-codoped oxyhalide tellurite glasses

Thermal stability, Raman spectra and blue upconversion luminescence properties of Tm-3divided by /Yb-3divided by -codoped halide modified tellurite glasses have been Studied. The results showed that the mixed halide modified tellurite glass (TFCB) has the best thermal stability, the lowest phonon energies and the strongest upconversion emissions. The effect of halide on upconversion intensity is observed and discussed and possible upconversion mechanisms are evaluated. The intense blue upconversion luminescence of Tin (3+) in TFCB Glass may be a potentially useful material for developing upconversion optical devices.. (C) 2004 Elsevier Ltd. All rights reserved.

Upconversion luminescence and mechanisms of Tm3+/Yb3+-codoped oxyhalide tellurite glasses

To obtain efficient blue upconversion laser glasses, upconversion luminescence and mechanisms of Tm3+/Yb3+-codoped oxyhalide tellurite glasses were investigated under 980nm excitation. The results showed that upconversion blue and red emission intensities of Tm3+ first increase, reach its maximum at TM2O3% =0.1 mol%, and then decrease with increasing Tm2O3 content. The effect of TM2O3 content on upconversion intensity is discussed, and possible effect mechanisms are evaluated. The investigated results were conducing to increase upconversion luminescence efficiency of Tm3+. (c) 2005 Elsevier B.V. All rights reserved.

Intense upconversion luminescence in ytterbium-sensitized thulium-doped novel oxychloride bismuth-germanium glass

Structural and up-conversion fluorescence properties in ytterbium-sensitized thulium-doped novel oxychloride bismuth-germanium glass have been studied. The structure of novel bismuth-germanium glass was investigated by peak-deconvolution of Raman spectrum, and the structural information was obtained from the peak wave numbers. The Raman spectrum investigation indicates that PbCl2 plays an important role in the formation of glass network, and has an important influence on the up-conversion luminescence. Intense blue and weak red emissions centered at 477 and 650 mn, corresponding to the transitions 1G(4) -> H-3(6) and (1)G(4) -> H-3(4), respectively, were observed at room temperature. The possible up-conversion mechanisms are discussed and estimated. This novel oxychloride bismuth-germanium glass with low maximum phonon energy (similar to 730 cm(-1)) can be used as potential host material for up-conversion lasers. (c) 2005 Elsevier Ltd. All rights reserved.