CRYSTAL CHEMICAL DESIGN OF ACTIVATED EUROPIUM(III) PHOSPHORS WITH SCHEELITE STRUCTURE

For the first time, the relationship between the features of the crystal structure and the luminescent properties of a series of molybdates, vanadates, and mixed vanadate-molybdates with a scheelite structure has been systemati­cally analyzed. Using the solid-state reaction method, CaMoO₄, KBi(MoO₄)₂, and BiVO₄, as well as solid solutions K₀.₄₅Bi₀.₅₅Mo₀.₉V₀.₁O₄, Ca₀.₁Bi₀.₉Mo₀.₁V₀.₉O₄, Bi₀.₉₈V₀.₉Mo₀.₁O₄ do­ped with 0.1 mol% Eu³+, have been synthesized. The degree of distortion of the coordination environment of molybdate, vanadate, and mixed vanadate-molybdatetetrahedrain the investigated structures was calculated based on X-ray diffraction data using the Shape 2.0 software via the continuous shape measure method. Analysis of luminescence spectra reveals that the transition from molybdates to vanadates leads to a noticeable red shift of the 5D₀→⁷F₂ transition bands in to the longer-wave length region of the spectrum. For a series of substituted members of the scheelite family, the following common features in the spectral characteristics of europium(III)-doped frameworks can be identified: 1)the red luminescence of all studied scheelite-structured matrices is characterized by predominant emission in the 610–620 nm region, corresponding to the electronic 5D₀→⁷F₂ transition; 2) the coordination environment of the luminescent centersis significantly more distorted than expected for the tetragonal phase of scheelite, even under monoclinic distortion. It was demonstrated that aliovalent substitution with in the anionic and cationic sublattices is one of the key approaches to modifying not only the local structure of the scheelite frame work but also a factor in fluencing the luminescent properties of oxide phosphors. Particular importance is attributed to local changes not only in the first coordination sphere of the luminescent ion but also in the second sphere, which includes mixed tetrahedral anions (Mo/V)O₄. This regularity can serveas the basis for the controlled tuning of luminescence line intensity ratios (color coordinates) and forenhancing the emission efficiency of oxide crystal phosphors.