Synthesis and characterization of structural and luminescence properties of blue — green BaAlxOy:Eu2+ phosphor by solution — combustion method

Abstract

Europium-doped barium aluminate (BaAlxOy:Eu2+) phosphors were obtained at low temperatures (500°C) using the solution — combustion of corresponding metal nitrate-urea solution mixtures. The particle size and morphology and the structural and luminescent properties of the synthesized phosphors were examined by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Electron diffraction spectroscopy (EDS) and photoluminescence (PL). It was found that the change in Ba: Al molar ratios showed greatly influence not only on the particle size and morphology, but also on their PL spectra and crystalline structure. The structure of BaAlxOy nanophosphors changes from a hexagonal Ba2Al10O17 phase for samples with 6:100 molar ratios to a hexagonal BaAl2O4 one with an increase in Ba content. The peak of the emission band occurs at a longer wavelength (around 615 nm) with a decrease in Ba concentration but displays a broad blue-green emission band composed from two emissions with the maximum at 495 and 530nm coming from Eu2+ in two sites for increasing Ba content. The blue-green emission is probably due to the influence of 5d electron states of Eu2+ in the crystal field because of atomic size variation causing crystal defects while the red emission is due to f - f transitions. These findings clearly demonstrate the possibility of fine tuning the colour emission.

Primary phases in aluminous slags produced by the aluminothermic reduction of pyrochlore

“…3) cannot be identified because of the potentially large number of activator cations in the interlayer regions. The presence of a single emission band suggests Mn 2+ or Eu 2+ might be activators as similar emission bands have been observed in a variety of barium and strontium aluminates (Dejene and Kebede, 2012;Xing et al 2006;Ravichandran et al, 1999). The single emission band rules out heavy REE such as Dy and Tb as activators which typically produce several very sharp CL emission lines over a wide range of wavelengths.…”

Spectral and kinetic properties of electroluminescence of ZnS:Cu powder in polymer structure

“…The authors found that at low excitation frequency the green emission is more intense, while over 1 kHz the blue band predominates over the green one. In the light of In the luminescence investigations, kinetic measurements are very important because they provide much information concerning the luminescent centers and the mechanism of luminescence in general [8][9][10][11][12]. Especially important are the measurements of luminescence excited by a constant pulse, for example, voltage, during as well as after the end of the pulse [9][10][11][12].…”

Bluish-green afterglow and blue photoluminescence of undoped BaAl2O4

“…4 Irrespective of the difference in Re, the PL spectra of BaAl 2 O 4 :Eu 2+ ,Re 3+ are similar to that of Eu 2+ doped BaAl 2 O 4 (BaAl 2 O 4 :Eu 2+ ). 11–14 Consequently, Eu 2+ is generally assumed to be the luminescent center of afterglow and the luminescent center of PL for BaAl 2 O 4 :Eu 2+ and BaAl 2 O 4 :Eu 2+ ,Re 3+ . 1–18…”

“…11–14 Consequently, Eu 2+ is generally assumed to be the luminescent center of afterglow and the luminescent center of PL for BaAl 2 O 4 :Eu 2+ and BaAl 2 O 4 :Eu 2+ ,Re 3+ . 1–18…”

“…4 Irrespective of the difference in Re, the PL spectra of BaAl 2 O 4 :Eu 2+ ,Re 3+ are similar to that of Eu 2+ doped BaAl 2 O 4 (BaAl 2 O 4 :Eu 2+ ). [11][12][13][14] Consequently, Eu 2+ is generally assumed to be the luminescent center of aerglow and the luminescent center of PL for BaAl 2 O 4 :Eu 2+ and BaAl 2 O 4 :Eu 2+ ,Re 3+ . [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] This belief is, however, challenged by a number of theoretical and experimental results: (i) both undoped SrAl 2 O 4 and Eu 2+ doped SrAl 2 O 4 exhibit quite similar green aerglow; 19 (ii) both undoped CaAl 2 O 4 and Eu 2+ doped CaAl 2 O 4 exhibit quite similar blue aerglow; 20,21 (iii) the peak of the aerglow spectrum of Eu 2+ doped CaAl 2 O 4 does not shi regardless the variation in doping concentration; 22 (iv) the green aerglow of Dy 3+ doped SrAl 2 O 4 and Tb 3+ doped SrAl 2 O 4 is quite similar to the aerglow of Eu 2+ doped SrAl 2 O 4 ; [23][24][25][26] (v) Dy 3+ doped BaAl 2 O 4 exhibits bluish-green aerglow which is quite similar to that of BaAl 2 O 4 :Eu 2+ ; 7 (vi) density functional theory (DFT) calculations demonstrate that the aerglows of undoped SrAl 2 O 4 , undoped CaAl 2 O 4 and Eu 2+ doped SrAl 2 O 4 originate from oxygen vacancy and cation vacancy in the hosts; [19][20][21]27 (vii) oxygen vacancies are held responsible for the aerglows of a number of undoped inorganic materials such as HfO 2 , 28 SrAl 2 O 4 , 19...…”