Nonlinear Composition-Dependent Optical Spectroscopy of Ba2xSr2-2xV2O7.

In general, adjusting the composition of a fluorescent material is an effective way to tune its luminescent properties such as peak energy and bandwidth. In most solid-solutions, the emission peak shifts linearly with the materials' composition, which is referred to as Vegard's Law. However, we found extraordinary variations in our samples Ba2xSr2-2xV2O7, that is, both the excitation and emission peaks show nonlinear dependence on the composition x, and the same is true for the spectral bandwidths. The nonlinearities are not due to structural anomaly, as all the samples are confirmed to be solid-solutions by X-ray diffraction measurements. To explain these phenomena, we proposed a model by considering the disorder of Ba(2+) and Sr(2+) distributions in solid-solutions and the changes of configurations between the ground and excited electronic states. This novel phenomenon could be applied to further exploit new fluorescent materials.