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The hitherto unknown title compound is prepared from a homogeneous melt of Na2O and P2O5 containing more than 25 wt.% of TiO2, which is slowly cooled down starting from 930 °C. An X‐ray analysis of this compound reveals that its space group is P21a; Z=4.

Luminescence and luminescence excitation under VUV radiation of ABP 2 O 7 (A = Na, K, Cs; B = Al, In) double phosphates are studied. Two emission bands peaking near 330 and 420 nm are common for investigated ABP 2 O 7 crystals. The band structure and partial densities of electronic states of perfect KAlP 2 O 7 , LiInP 2 O 7 and NaTiP 2 O 7 crystals are calculated by the full-potential linear-augmented-plane-wave (FLAPW) method. It is found that the structures of the conduction bands of ABP 2 O 7 crystals, which have different B cations, are appreciably different. Experimental results are compared with results of calculations of the electronic structure. Assumptions concerning the origin of luminescence in double phosphates are made.

PACS 77.84.Bw, 78.55.Hx Sodium titanium orthophosphate NaTi 2 (PO 4 ) 3 crystals were synthesized and their luminescence properties were investigated. Luminescence spectra of this compound consist of two main bands in the green and red spectral regions. Maximum positions of the bands depend on temperature of the samples. At some conditions the red band reveals details of a fine spectra structure. Obtained results are discussed taking into account similarity of spectral properties of the investigated crystals with ones described recently for sodium aluminum diphosphate crystals doped with chromium ions. Conclusion is made that red emission band is corresponded to radiation transitions in the Ti 3+ titanium ions.