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The Ca 9 Y(VO 4 ) 7-x (PO 4 ) x (x = 0, 1, 3, 4) solid solution whitlockite-like single crystals have been grown by the Czochralski method from mixtures of single phase Ca 9 Y(VO 4 ) 7 and Ca 9 Y(PO 4 ) 7 starting materials produced by solid-state synthesis. Real compositions of solid solution crystals has been determined and analyzed. It is found that crystals with x = 0, 1, 4 exist with polar structure at room temperature, space group R 3 c . At least one of them, Ca 9 Y(VO 4 ) 7 , demonstrates ferroelectric behaviour with phase transition at 942 °C. Unlike the others, Ca 9 Y(VO 4 ) 3 (PO 4 ) 4 crystallizes in centrosymmetric whitlockite-like structure with space group R 3 ¯ c confirmed by single-crystal X-ray structure analysis. Similar to other whitlockite-family phosphates and vanadates, its crystal structure is described as a disordered structural version of usual whitlockites, corresponding to their high-temperature paraelectric phases. The transmission and luminescence spectra of solid solution crystals are reported, the hardness H v and fracture toughness K 1c of solid solution single crystals are also determined.

Ca9Nd(VO4)7 single crystal was grown by the Czochralski method in inert atmosphere. The crystal structure and chemical composition were studied. Polarized absorption and luminescence spectra were investigated in details. It was found that the Ca9Nd(VO4)7 crystals belongs to self-activated laser materials with a weak concentration quenching of luminescence. Judd-Ofelt analysis was performed. The emission cross-sections spectra for 4F3/2 → 4I9/2, 4I11/2, 4I13/2 transitions were determined. For the first time Raman spectra of the Ca9Nd(VO4)7 single crystal were recorded and interpreted.

Pure and Yb-doped Ca 9 Y(VO 4 ) 7 (CYVO) single crystals were grown using the Czochralski method. Their crystal structure was determined using powder diffraction and the defect structure was characterized using high-resolution diffraction. The undoped crystal is found to be composed of a transparent and an opaque parts. In the latter, yttrium-rich inclusions were detected. Spectral-kinetic characteristics of Yb3 -doped crystals is reported.