Abstract
Objectives. This study aimed to predict the limits of substitution and stability of luminescent materials based on low-temperature modifications of solid solutions (spatial group P21/c) with lutetium oxyorthosilicates (Lu1−xLnx)[(SiO4)0.5O0.5], where Ln represents the rare-earth elements (REEs) of the La–Yb series.Methods. The V.S. Urusov’s crystal energy theory of isomorphous substitutions and a crystallochemical approach in the regular solid solution approximation were used to calculate the energies of the mixing (interaction parameters) of the solid solutions.Results. Using the V.S. Urusov’s theory, we calculated the energies of mixing (interaction parameters) in the systems under study. The dependences of the decomposition temperatures of solid solutions on the REE number and composition (x) were obtained and used to create a diagram of the thermodynamic stability of the solid solutions, allowing us to predict the substitution limits depending on the temperature or determine the decomposition temperature using the given substitution limits.Conclusions. The results of the study can be useful when choosing the ratio of components in matrices (host materials) and the amount of the activator (dopant) in the new luminescent, laser, and other materials based on low-temperature modifications of solid solutions of “mixed” REE oxyorthosilicates (Lu1−xLnx)[(SiO4)0.5O0.5].
Highlights
Oxyorthosilicates of rare-earth elements (REEs), Ln[(SiO4)0.5O0.5], and solid solutions (Lu1−xLnx)[(SiO4)0.5O0.5] have attracted the attention of researchers, as they can be applied as materials for producing luminophores [1, 2], scintillators [3,4,5,6,7], lasers [8], among other purposes
The electronegativity of Lu, as in the case of Gd, is significantly low. Such a change in the χLn of REEs leads to a situation wherein the differences in the degrees of ionicity of the chemical bonds vary within the range of 0.001–0.019 and do not significantly affect the total energy of mixing, which decreases with increase in the REE number
A crystallochemical approach in the regular solution approximation was used to calculate the energies of mixing of solid solutions, which were based on the lowtemperature modification of lutetium oxyorthosilicate Lu[(SiO4)0.5O0.5] and modified with REEs for compositions with x = 0.01, 0.03, 0.05, 0.10, 0.20, and 0.5
Summary
Oxyorthosilicates of rare-earth elements (REEs), Ln[(SiO4)0.5O0.5], and solid solutions (Lu1−xLnx)[(SiO4)0.5O0.5] have attracted the attention of researchers, as they can be applied as materials for producing luminophores [1, 2], scintillators [3,4,5,6,7], lasers [8], among other purposes. The authors of [1] established that the oxyorthosilicates of the yttrium subgroup can be obtained as a lowtemperature modification (1173–1273 K) of nanosized polycrystals (space group P21/c) In this case, they are isostructural crystals of the cerium subgroup. The study of luminescent properties showed that the polycrystalline oxyorthosilicate Lu[(SiO4)0.5O0.5]:Ce had better spatial resolution and image sharpness than luminophore Gd2O2Si:Tb, which has been used in most medical imaging methods in the last decades [6] This luminophore can be used in X-ray mammography for visualization in both radiographic cassettes and digital detectors. It has an excellent spectral compatibility with the currently used Si-based films
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