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Different compositions of europium doped aluminosilicate oxyfluoride glass ceramics prepared in air atmosphere have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy methods. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements show presence of homogenously distributed SrF2 nanocrystals after the heat treatment of the precursor glass. Efficient Eu 3+ incorporation in the high symmetry environment of glass ceramics is observed from the photoluminescence spectra. EPR spectra indicate Eu 3+ → Eu 2+ reduction upon precipitation of crystalline phases in the glass matrix. For composition abundant with Eu 2+ in the glassy state such behaviour is not detected. Local structure around europium ions is discussed based on differences in chemical compositions.

Solid solutions with fine-tunable photoluminescence have been obtained in a 4-iodothioxanthone−4-chlorothioxanthone system. Both pure components are room-temperature luminophors demonstrating different luminescence properties. It was discovered that in the 4-chlorothioxanthone structure, up to half of the molecules can be replaced by the iodo analogue obtaining solid solutions in the respective composition range. Despite this solid solution existing in such a large composition range, the variation of the luminescence spectra is not substantial. In the 4-iodothioxanthone structure, only up to ∼20% of the molecules can be replaced by the chloro analogue before the composition limit of this solid solution is reached. In contrast, there is a strong composition-dependent response of the luminescence. A considerable change in luminescence spectra is observed even if only a few mol % of the opposite component is added. The spectra of mechanical mixtures of pure components are different from those of the solid solutions, which demonstrates the unique behavior of the newly obtained solid phases. This study shows great potential to use solid solution engineering in the organic solid state to tune material properties in a continuum as opposed to other crystal engineering approaches, leading to property tunability in a stepwise fashion.

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