Computational and Experimental Study of Gd-substituted Scandium Orthovanadate Systems

The energies of mixing (interaction parameters) and critical decomposition temperatures of $\mathrm{S}\mathrm{c}{}_{1-x}\mathrm{L}\mathrm{n}_{x}\mathrm{V}\mathrm{O}_{4}$ solid solutions (where Ln is a rare-earth element (REE), Ln=Ce- Lu) with the zircon structure were calculated using the crystal-energy theory of isomorphous miscibility. Decomposition temperatures for $\mathrm{S}\mathrm{c}{}_{1-x}\mathrm{L}\mathrm{n}_{x}\mathrm{V}\mathrm{O}_{4}$ solid solutions with x=0.01,0.02,0.05,0.10, and 0.20 were calculated with crystal chemical method of regular solution approximation. A diagram which allows to determine decomposition temperature with given equilibrium substitution limit (x), or substitution limit with given temperature and assess areas of stability, instability, and metastability for $\mathrm{S}\mathrm{c}{}_{1-x}\mathrm{L}\mathrm{n}_{x}\mathrm{V}\mathrm{O}_{4}$ solid solutions is presented. Results of calculations were compared with literature data on thermodynamic stability of solid solutions and on substitution limits. The results of the study can be used during development of new luminescent materials based on $\mathrm{S}\mathrm{c}\mathrm{V}\mathrm{O}_{4}$, which are modified with rare-earth elements, at defining rare-earth elements in matrix and activator, at defining optimal proportions of REE in $\mathrm{S}\mathrm{c}{}_{1-x}\mathrm{L}\mathrm{n}_{x}\mathrm{V}\mathrm{O}_{4}$ matrixes. Using the XRD method, including the Rietveld structure refinement was found that the substitutional limit of Gd for Sc (x) in a series of solid solutions $\mathrm{S}\mathrm{c}1-x\mathrm{G}\mathrm{d}_{X}\mathrm{V}\mathrm{O}_{4}$ is about 0.13, which is in satisfactory agreement with the result of the calculation (x=0.18). The effect of substitutions on the luminescent properties of $\mathrm{S}_{\mathrm{C}1-x}\mathrm{G}\mathrm{d}_{x}\mathrm{V}\mathrm{O}_{4}$ is shown: with the introduction of 9% Gd in $\mathrm{S}\mathrm{c}\mathrm{V}\mathrm{O}_{4}$, the intensity of intrinsic luminescent radiation increases to a greater degree.