Luminescence Characteristics of LaAlO3:Eu3+ Obtained by Modified Pechini’s Method (original) (raw)
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Solid State Sciences, 2011
Europium-doped lanthanum aluminate (LaAlO 3 ) powder was prepared by using a combustion method. The crystallization, surface morphology, specific surface area and luminescence properties of the samples have been investigated. Photoluminescence studies of Eu doped LaAlO 3 showed orange-reddish emission due to Eu 3þ ions. LaAlO 3 :Eu 3þ exhibits one thermally stimulated luminescence (TSL) peak around 400 C. Room temperature electron spin resonance spectrum of irradiated phosphor appears to be a superposition of two centres. One of them (centre I) with principal g-value 2.017 is identified as an O À centre while centre II with an isotropic g-value 2.011 is assigned to an F þ centre (singly ionized oxygen vacancy). An additional defect centre observed during thermal annealing around 300 C grows with the annealing temperature. This centre (assigned to F þ centre) originates from an F-centre (oxygen vacancy with two electrons) and the F-centre along with the associated F þ centre appear to correlate with the observed TSL peak in LaAlO 3 :Eu 3þ phosphor. The activation energy for this peak has been determined to be 1.54 eV from TSL data.
Synthesis and luminescence properties of Eu 3+-doped LaAlO 3 nanocrystals
Journal of Alloys and Compounds, 2006
Eu 3+ /Dy 3+ ions co-doped Ca 2 La 8 (GeO 4 ) 6 O 2 (CLGO) phosphors were prepared by a pechini-type sol-gel method. The structural and morphological studies of the CLGO phosphors were carried out by measuring X-ray diffraction patterns and scanning electron microscope images. The photoluminescence (PL) spectra of the CLGO:Eu 3+ phosphor exhibited the intense red emission due to the electric-dipole transition while the CLGO:Dy 3+ phosphor showed the blue ( 4 F 9/2 ? 6 H 15/2 ) and yellow ( 4 F 9/2 ? 6 H 13/2 ) emissions with almost equal intensities. The Eu 3+ /Dy 3+ ions co-doped CLGO phosphor showed the improved white light by shifting towards the warm white region. The energy transfer from Dy 3+ to Eu 3+ ions was investigated by means of PL intensities. The lifetime measurements were also performed for single-doped and codoped samples. The calculated chromaticity coordinates indicated that these phosphors may be suitable for the fabrication of near-UV excitation-based white light-emitting diodes.
A B S T R A C T We synthesized the trivalent europium ions (Eu 3+) doped lanthanum aluminate (LaAlO 3 , LAO) nanophosphors by a solvothermal method. Their structural, morphological, and luminescent properties were systematically investigated. The obtained nanoparticles possessed single nanocrystallinity with a rhombohedral structure. For the excitation originating from the charge transfer band (O 2-to Eu 3+ ions) under 320 nm illumination, the featured emissions of Eu 3+ ions were detected in all the compounds. The optimum doping concentration of Eu 3+ ions in LAO was about 9 mol% and the concentration quenching was dominated by dipole-dipole interaction. Furthermore, the Judd-Ofelt (J-O) theory was used to estimate the J-O intensity parameters. Based on the temperature-dependent PL emission spectra, the thermal stability was analyzed and the activation energy was obtained to be 0.234 eV. Meanwhile, the decay time, color coordinate/purity, and cathodoluminescence behaviors of the synthesized nanophosphors were also studied. These characteristics make the Eu 3+-doped LAO nanoparticles a promising red-emitting phosphor for both ultraviolet-based white light-emitting diodes and field-emission displays.
Journal of Applied Physics, 2009
In this work we studied the structural and optical properties of lithium tantalate ͑LiTaO 3 ͒ powders doped with Eu 3+ ions. We have examined the different sites occupied by the rare earth ion through the correlation of the DRX data analyzed with the Rietveld method and some spectroscopic parameters derived from the Eu 3+ luminescence. A direct relation was established between the lattice parameters and the "occupation fraction" of Eu 3+ in each LiTaO 3 site. The occupation fraction was set as the relative population of Eu 3+ ions for each site obtained by means of the intensity, baricenter, and the spontaneous emission coefficients of the 5 D 0 → 7 F 0 transitions. We concluded that the unit cell parameter a presents the same behavior of the Eu 3+ occupation fraction in Ta 5+ sites as a function of the Eu 3+ content in LiTaO 3. The same was observed for the variation in Eu 3+ occupation fraction in the Li + site and the unit cell parameter c with the Eu 3+ content.
Sol–gel Pechini synthesis and optical spectroscopy of nanocrystalline La2O3 doped with Eu3+
Optical Materials, 2010
Europium-doped La 2 O 3 nanocrystalline powders with sizes in the range of 50-200 nm have been obtained by the modified sol-gel Pechini method. Differential thermal analysis, thermogravimetric analysis, infrared spectroscopy and X-ray diffraction were used to study the evolution of the precursor powders towards the desired crystalline phase. We determined the size and the morphology of the nanoparticles by electronic microscopy. Finally, we studied and analyzed the luminescence properties of the trivalent europium in the hexagonal La 2 O 3 nanocrystals by photoluminescence and cathodoluminescence. The luminescence spectrum of Eu 3+ in these nanocrystals is dominated by the 5 D 0 ? 7 F 2 transition with its maximum intensity peak located at 626 nm, which makes of these nanocrystals promising nanophosphors emitting in the red region of the electromagnetic spectrum.
The concentration quenching of photoluminescence in Eu3+-doped La2O3
This work explores the influence of dopant concentration on photoluminescent emission and kinetics of Eu 3+ -doped (0.2−10 at.%) nanocrystalline lanthanumoxide powders. The X-ray diffraction analysis confirmed that all samples crystallize in La 2 O 3 hexagonal phase with space group P3m1. Transmission electron microscopy showed particles with non-uniform shape and diverse size distribution with an average particle size of (95 ± 5) nm. The room temperature photoluminescence spectra of all samples contain characteristic Eu 3+ luminescence lines with the most pronounced red 5 D 0 → 7 F 2 emission at about 626 nm. The maximum intensity of red emission is observed for the sample containing 5 at.% of Eu 3+ ions. The emission kinetics was recorded in the temperature range from 10 K to 300 K. The maximum lifetime value of 0.98 ms obtained for the sample with 0.5 at.% Eu 3+ at room temperature increases up to 1.3 ms at 10 K.
Journal of Applied Physics, 2007
The luminescence properties of Eu 3+ :Al 2 O 3 powders prepared via low temperature direct combustion synthesis was investigated. It was observed that the heat treatment of the powders modifies the dynamics of the radiative transition 5 D 0 → 7 F 2 of Eu 3+ ͑1.0 mol % ͒ and produces an enhancement of the luminescence intensity by nearly one order of magnitude. The luminescence enhancement is attributed to the presence of Eu 3+ in ␣-Al 2 O 3 crystalline phase as the heat treatment drastically reduces the amount of amorphous Al 2 O 3 phases present in the powder.
Vi Encuentro Franco-Espanol De Quimica Y Fisica Del Estado Solido - Vi Rencontre Franco-Espagnole Sur La Chimie Et La Physique De L Etat Solide, 2010
Europium-doped La 2 O 3 nanocrystalline powders with sizes ranging from 4 nm to 300 nm have been obtained by the modified Pechini, hydrothermal with conventional furnace, hydrothermal with microwave furnace, and precipitation with ultrasonic bath methods. X-ray diffraction techniques were used to study the evolution of the prepared gels towards the desired crystalline phase. We determined the size and the morphology of the nanoparticles by electronic microscopy. Finally, we studied and analyzed the luminescence properties of the trivalent europium in the hexagonal La 2 O 3 nanocrystals by photoluminescence and cathodoluminescence.
LaAlO3:Eu3+ and LaAlO3:Tb3+ phosphors were prepared by microwave-induced combustion reaction. X-ray diffraction (XRD), scanning electron microscopy (SEN) and photoluminescence spectroscopy (PL) were used to characterize the produced powders. X-ray diffraction patterns confirmed the formation of nanocrystalline LaAlO3 oxide. Traces of secondary phase, La(OH)3, were observed in the pattern of the sample doped with terbium. Under UV excitation, Eu3+ and Tb3+-doped LaAlO3 phosphors show red and blue/green photoluminescence, respectively. These systems are potential candidates for use as luminescent materials.