Growth and characterization of Na3R(BO3)(2) (R = La-Gd) borates: crystal structure, high-temperature behavior, and optical properties

Na3R(BO3)(2) (R = La-Gd) borates, grown with Na2O-B2O3-NaF flux, crystallize in the space group P2(1)/n. Contrary to previously published data, the peaks in the 980(La)-950(Gd) degrees C range are attributed to phase transition process, while the melting process occurs at about 100 degrees higher. Another feature of thermal behavior consists of the gradual decomposition of the compound into Na3R2(BO3)(3). The end member in the decomposition series is Na2R2O(BO3)(2), which originates under oxygen/water atmosphere. In addition, the components of the thermal expansion tensor and the dependings of the unit-cell parameters of Na3Nd(BO3)(2) on temperature were defined. A series of Pr3+, Nd3+, and Sm3+-doped Na3Gd(BO3)(2) (NGB) borates were prepared from mixtures of grown crystals by solid-state synthesis, and their photoluminescence properties were studied in detail. The excitation and emission spectra of NGB: Pr3+ and NGB: Nd3+ are comparable with similar compounds, and the relative intensity reaches the maximum at 1 mol% of Pr3+, Sm3+, and 10 mol.% for Nd3+ doping.