Abstract
Herein we describe the synthesis, crystal structures, photoluminescence (PL) and cathodoluminescence (CL) spectra of phosphors in the Sr0.97-xBaxEu0.03Al2O4 system between x = 0 and x = 0.97. The syntheses of these phosphors were carried out by solid state reactions at 1350°C in mixed gas (H2/N2). The molar fractions of the alkaline earth elements were varied in steps of 0.1. The Sr1-xBaxAl2O4 series manifested solid solutions of a monoclinic phase (at the Sr-rich side) and a hexagonal phase (at the Ba-rich side). At the Ba-rich side of Srx-1BaxAl2O4:Eu2+ we found evidence in the PL spectra that the hexagonal phase differed as the xBa fraction changed: it changed at room temperature from the ferroelectric P63 structure at xBa=1 to the paraelectric P6322 phase at xBa≈0.9 and at xBa≈0.8 it went back to P63. Unlike the PL spectra, the CL spectra of the hexagonal phase of Sr0.97-xBaxEu0.03Al2O4 at x ≥ 0.5 indicated only the paraelectric P6322 phase at room temperature.
Highlights
As part of an ongoing study on metal aluminate phosphors activated with Eu2+ we have investigated the luminescence of the phosphor series Ba1−xSrxAl2O4, Sr1−xCaxAl2O4 and Ba1−xCaxAl2O4 doped with Eu2+
The crystalline phases of the products were determined by X-ray powder diffraction at room temperature using Bruke’s D8 Advance X-ray diffraction (XRD) equipment fitted with a nickelfiltered copper source, CuKα at λ=1.5406 Å, and a LynxEye silicon strip detector
The particle size of the alkaline earth aluminates after the high temperature annealing process was in all cases rather large and varied from about 1 to 6 μm
Summary
As part of an ongoing study on metal aluminate phosphors activated with Eu2+ we have investigated the luminescence of the phosphor series Ba1−xSrxAl2O4, Sr1−xCaxAl2O4 and Ba1−xCaxAl2O4 doped with Eu2+. We shall describe the results for Sr1−xCaxAl2O4, the results for Ba1−xSrxAl2O4 and Ba1−xCaxAl2O4 will be published separately In consequence of their rather high photoluminescence (PL) efficiency the alkaline earth (Ca, Sr or Ba) aluminates doped with Eu2+ have been extensively studied [1]. From the first decade of the last century onwards, alkaline earth aluminates have been intensively studied for their use in cements These are refractory materials and were traditionally prepared by solid state reactions at high temperature (1200-1600°C) [13,14]. The PL spectra of the system CSA doped with 5 mol% Eu2+ and 5 mol% Dy3+ have been published by Xie et al [36] The phases they found largely confirmed the results of Prodjosantoso and Kennedy and Pöllmann and Kaden. In view of the scarcity of literature on the luminescent properties of CSA doped with only Eu2+ and the scientific debate over the origin of the two luminescence bands of SrAl2O4:Eu2+, we decided to investigate the mixed aluminates doped with Eu2+ in more detail
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