High-pressure/high-temperature synthesis, single-crystal structure analysis, and spectroscopic data of γ-Eu(BO₂)₃ and γ-Gd(BO₂)₃

Orthorhombic crystals of the compounds γ -Eu(BO 2 ) 3 and γ -Gd(BO 2 ) 3 were obtained by high-pressure/high-temperature syntheses at 10.5 GPa and 1100 and 900 °C, respectively. The structures were solved by single-crystal X-ray diffraction methods. The two compounds crystallize with four formula units per cell in the space group Pca 2 1 (no. 29) with the unit cell parameters a = 18.2729(7), b = 4.4076(2), c = 4.2505(1) Å ( Ln = Eu), and a = 18.2591(6), b = 4.4055(1), c = 4.2477(1) Å ( Ln = Gd). Their infrared spectra and the luminescence spectrum of γ -Eu(BO 2 ) 3 are discussed.