Eu2+Eu2+ luminescence in the EuAl2O4EuAl2O4 concentrated phosphor (original) (raw)
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Eu 2 + luminescence in the EuAl 2 O 4 concentrated phosphor
Radiation Measurements, 2007
Powder samples of EuAl 2 O 4 and (Eu, Sr)Al 2 O 4 with a quantum efficiency (QE) of the Eu 2+ emission more than 0.30 were synthesized. A modified method of QE determination is described and results of the QE measurements for EuAl 2 O 4 , (Eu 0.8 Sr 0.2 )Al 2 O 4 , (Eu 0.65 Sr 0.35 )Al 2 O 4 , and a diluted sample (Sr 0.98 Eu 0.02 )Al 2 O 4 are presented. Excitation and emission spectra as well as decay behaviour of the Eu 2+ luminescence in (Eu 1−x Sr x )Al 2 O 4 in the temperature region of 20-300 K are studied. It is concluded that the main reason for the high QE is a pronounced relaxation of the crystal lattice after excitation of the Eu 2+ ions resulting in an emission with a large Stokes shift and, therefore, in a restriction of energy migration. Eu ions occupying the crystallographic sites with the higher coordination number (Eu II ) are supposed to be the luminescence centres in (EuSr)Al 2 O 4 lattice.
Luminescence in the Concentrated Phosphor
Radiation Measurements, 2007
Powder samples of EuAl 2 O 4 and (Eu, Sr)Al 2 O 4 with a quantum efficiency (QE) of the Eu 2+ emission more than 0.30 were synthesized. A modified method of QE determination is described and results of the QE measurements for EuAl 2 O 4 , (Eu 0.8 Sr 0.2 )Al 2 O 4 , (Eu 0.65 Sr 0.35 )Al 2 O 4 , and a diluted sample (Sr 0.98 Eu 0.02 )Al 2 O 4 are presented. Excitation and emission spectra as well as decay behaviour of the Eu 2+ luminescence in (Eu 1−x Sr x )Al 2 O 4 in the temperature region of 20-300 K are studied. It is concluded that the main reason for the high QE is a pronounced relaxation of the crystal lattice after excitation of the Eu 2+ ions resulting in an emission with a large Stokes shift and, therefore, in a restriction of energy migration. Eu ions occupying the crystallographic sites with the higher coordination number (Eu II ) are supposed to be the luminescence centres in (EuSr)Al 2 O 4 lattice.
Journal of Non-crystalline Solids, 2009
Strong blue-green light emitting Eu doped SrAl 2 O 4 phosphor was synthesized by a low-temperature initiated, self-propagating and gas producing combustion process in a very short time (<5 min). The prepared powder was characterized by X-ray diffraction, Fourier-transform infrared spectrometry and scanning electron microscopy. The excitation spectrum shows a peak at 397 nm. Upon excitation at 397 nm, the emission spectrum exhibits a well defined broad band with maximum at 493 nm corresponding to 4f 6 5d ? 4f 7 transition. Electron paramagnetic resonance (EPR) measurements at X-band showed low field signals due to Eu 2+ ions in SrAl 2 O 4 :Eu.
New localized/delocalized emitting state of Eu2+ in orange-emitting hexagonal EuAl2O4
Scientific reports, 2014
Eu(2+)-activated phosphors are being widely used in illuminations and displays. Some of these phosphors feature an extremely broad and red-shifted Eu(2+) emission band; however, convincing explanation of this phenomenon is lacking. Here we report a new localized/delocalized emitting state of Eu(2+) ions in a new hexagonal EuAl(2)O(4) phosphor whose Eu(2+) luminescence exhibits a very large bandwidth and an extremely large Stokes shift. At 77 K, two luminescent sites responsible for 550 nm and 645 nm broadband emissions are recognized, while at room temperature only the 645 nm emission band emits. The 645 nm emission exhibits a typical radiative lifetime of 1.27 μs and an unusually large Stokes shift of 0.92 eV. We identify the 645 nm emission as originating from a new type of emitting state whose composition is predominantly that of localized 4f(6)5d character but which also contains a complementary component with delocalized conduction-band-like character. This investigation provid...
High-pressure luminescence spectroscopy of EuAl2O4 phosphor
Radiation Measurements, 2007
EuAl 2 O 4 powder phosphor was prepared by solid-state reaction of EuO and Al 2 O 3 oxides in vacuum. The influence of conditions of preparation on spectral lineshape of Eu 2+ emission was analyzed. It was found that the fluorescence spectra of vacuum-prepared EuAl 2 O 4 samples at 300 K present the superposition of three bands peaked at 430, 500 and 528 nm, corresponding to the 4f 6 5d 1 → 4f 7 (8 S 7/2) transition of Eu 2+ ions in the different sites of EuAl 2 O 4 lattice. The luminescence of Eu 2+ centers in EuAl 2 O 4 host was also studied using the high-pressure spectroscopy up to 67 kbar. It was found that the bright green-yellow fluorescence of EuAl 2 O 4 at 300 K in the band peaked at 520.530 nm range can be presented by superposition of two Gaussian sub-bands. The different pressure shifts −23 and −27 cm −1 /kbar for two sub-bands were found. Such a structure of the emission spectrum was attributed to the existence of two different Eu 2+ centers in the Eu 2+ II sites of EuAl 2 O 4 lattice with higher coordination number.
Effect of Eu3+ Concentration on Luminescence Studies of Y4Al2O9 Phosphor
Indian Journal of Materials Science, 2014
The present paper reports the effect of europium concentration on photoluminescence (PL) and thermoluminescence (TL) studies of Eu3+ doped Y4Al2O9 phosphor using inorganic materials like yttrium oxide (Y2O3), aluminium oxide (Al2O3), boric acid (H3BO3) as a flux, and europium oxide (Eu2O3). The sample was prepared by the modified solid state reaction method, which is the most suitable for large-scale production. The prepared phosphor sample was characterized using X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEGSEM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL), thermoluminescence (TL), and CIE techniques. The PL emission was observed in the range of 467, 535, 591, 611, 625, and 629 nm for the Y4Al2O9 phosphor doped with Eu3+ (0.1 mol% to 2.5 mol%). Excitation spectrum was found at 237 and 268 nm. Sharp peaks were found around 591, 611, and 625 nm with high intensity. From the XRD data, using Scherer’s formula, the calculated av...
Luminescence of Eu3+ in α-Al2O3 powders
Journal of Alloys and Compounds, 2006
Low-temperature site-selective luminescence spectroscopy demonstrates that combustion synthesis can substitute Eu 3+ for Al 3+ in ␣-Al 2 O 3 , despite the large size discrepancy between these ions. The optical spectral features observed are commensurate with C 3v site symmetry of Eu 3+ . A comparative discussion is included with other preparation methods.
Structural and luminescence characteristics of Sr3Al8SiO17:Eu2+nanophosphor
This work presents the synthesis of Eu2+ doped novel Sr3Al8SiO17 phosphors by modified combustion technique. The luminescent properties of these phosphors have been explored by analyzing their excitation and emission spectra with the help of photoluminescence spectrometer at room temperature. The crystal structure of Sr3Al8SiO17 phosphor was refined using Rietveld method. Powder X-ray diffraction analysis shows the crystalline nature of the prepared phosphor which was later confirmed by transmission electron microscopy analysis having particle dimension in between 30 and 40 nm. The morphological structures and elemental analysis of the samples were conducted using scanning electron microscope coupled with energy dispersive spectroscopy. The presence of specific mode of vibrations of the phosphor was studied by fourier transform infrared spectroscopy. Under ultra-violet excitation, Sr3Al8SiO17 phosphors show broad-band emission spectrum peak at 486 nm in the blue region of the spectra corresponding to 4f65d1?4f7 transition of Eu2+ ion. The maximum photoluminescence intensity has been obtained for 0.3 mol% concentration of Eu2+ ion in Sr3Al8SiO17 (when monitored at an excitation wavelength of 354 nm it gives emission at 486 nm). The results show Sr3Al8SiO17:Eu2+ is a promising candidate for the phosphors and may be used for improving the efficiency and quality of phosphor-converted white light-emitting diodes.
New insights in the structure–luminescence relationship of Eu:SrAl2O4
Journal of Alloys and Compounds, 2009
This work aims the preparation of Eu:SrAl 2 O 4 through a sol-gel methodology. Some studies point out the possibility that hexagonal polymorph exhibit higher luminescence efficiency than the monoclinic one. However, the slow diffusion processes in the solid-state reactions require the use of fluxing agents, like B(III) ions, to reduce the synthesis temperature, thus favouring the formation of the monoclinic phase and avoiding the stabilization of the hexagonal one. For that, the synthesis proposed in this work allows to prepare pure hexagonal and monoclinic polymorphs without the use of any fluxing agent. The influence of Eu-doping level and firing temperature in the crystalline structure and optical properties of both polymorphs are studied by means of X-ray diffraction, Raman scattering, absorption, excitation and emission spectroscopy. Emission spectra reveal the existence of energy transfer between the monoclinic matrix and the Eu 2+ ion, but the luminescence efficiency is not influenced by the crystalline polymorph but it mainly depends on the firing temperature.
Laser excited long lasting luminescence in CaAl2O4: Eu3+/Eu2+ + Nd3+ phosphor
2013
The europium and neodymium oxides doped nano-structured calcium aluminate phosphor samples have prepared through combustion technique and their luminescence properties are studied using laser excitations. Samples prepared in open atmosphere showed the presence of both Eu3+ and Eu2+ states and their ratio changes with calcination temperature. Single Eu3+/Eu2+ ions doped sample has found to give broad emission at 450 nm without the persistence glow while the Eu3+ + Nd3+ ions codoped sample has shown persistence glow at 450 nm (Eu2+) on 355 nm laser excitation. Wavelength selective excitations show that 266 nm excitation gives the intense emissions from both Eu3+ and Eu2+ states with no afterglow but 355 nm excitation gives negligible emission from Eu3+ ions and a strong afterglow at 450 nm wavelength. The mechanism of wavelength dependent phosphorescence has been discussed. Studies on Stark splittings and their relative intensities in emission spectra of Eu3+ ions have shown that Eu3+ ion can be used as excellent probe of crystal structure.