Nanophosphor GdOBr:Ce via combustion synthesis: luminescence results.

We used combustion synthesis to produce phase pure GdOBr:Ce with varying Ce concentration. Several combinations of NH₄Br and fuel concentration were tested before phase pure GdOBr:Ce was produced by using a 50% excess of NH₄Br and a 50% lean concentration of fuel. In addition to the expected emissions from Ce and Gd, we also detected emissions from Eu³⁺ and Tb³⁺. Further research indicated that these extra rare earth emissions were due to impurities in the Gd₂O₃ starting material. While not the desired effect, we were able to monitor both Eu and Ce intensities as a function of Ce concentration in GdOBr. The Ce emission is seen to reach a maximum between 0.1 and 0.5 mol%. At higher Ce content, the Ce luminescence is quenched because of the concentration quenching effect and the higher concentration of O-H and N-H groups as revealed by IR spectra. Eu emission progressively decreases as Ce content increases from a combination of competition with Ce for charge capture in the RL process and the effect of OH and NH groups. As Ce concentration increases the RL intensity ratio of the bands of the Ce doublet changes even though the energy difference between the two bands (0.24 ± 0.1 eV) is compatible with the spin-orbit splitting of the ground level of Ce³⁺ (0.25 eV). Fitting results indicate that this relative change is not due to changes in self-absorption, and the effect may be due to changes in local symmetry of the Ce ion. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]