Synthesis of two new orthoborates KBaPr(BO3)2 and KBaNd(BO3)2

Two new rare-earth orthoborates KBaPr(BO3)2 and KBaNd(BO3)2 were synthesized using a two-step solid-state reaction, both of them are stable in the temperature range 850–1000°C. KBaNd(BO3)2 and KBaPr(BO3)2 show incongruent melting at 1019°С and 1005°С, respectively. Prepared compounds crystallize in the trigonal system with space group R3¯m with cell parameters of а =  5.5052(12) A, с =  18.402(8) A, Z = 3 for KBaPr(BO3)2 and cell parameters of а =  5.4956(5) A, с =  18.278(3) A, Z = 3 for KBaNd(BO3)2. These new borates continue the previously described line of isostructural three-cation orthoborates KBaY(BO3)2 and KBaR(BO3)2, by R  =  Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. The identity of the intensity and position of the bands in the IR spectra confirm that these compounds are isostructural and have high degree of homogeneity. A red emission centered at 700–740 nm under UV excitation was observed for synthesized KBaPr(BO3)2 powder.