Phaseformation in triple systems phosphates Sr–<i>M</i><sup>2+</sup>–<i>Ln</i><sup>3+</sup> (<i>M</i><s

The phase formation in a system of triple phosphates Sr–M2+–Ln3+ (M2+ = Zn2+, Mg2+, Mn2+; Ln3+ = Eu3+, Tb3+) has been investigated. The crystallization of strontiowhitlockite like structure and isomorphism in a series Sr9–xMnxTb(PO4)7, Sr9–xMgxEu(PO4)7 and Sr9–xZnxEu(PO4)7 (0 ≤ x ≤ 1.0) was described. The species were synthesized through solid-state reaction. It was shown that unlimited series of solid solutions can not be formed. The formation of a strontiowhitlockite-like structure was observed for only stoichiometric compositions Sr8MgEu(PO4)7 and Sr8ZnEu(PO4)7. Crystal chemical aspects of the formation of the strontiowhitlockite structure in the series were analysed. Samples with the strontiowhitlockite structure are crystallized in centrosymmetric space group (sp. gr. R3m) compared to a mother structure, mineral whitlockite, and its synthetic modifications based on calcium phosphate. The conditions for the formation of phosphates with the structure of stronciowhitlockite are indicated. The photoluminescence properties were described, and it was shown that samples exhibit intense emission in the red-orange region, due to the presence of Eu3+ ions. A quenching effect in Sr9–xMnxTb(PO4)7 was detected.