A new group of tetracyanidoborates - tetracyanidoborates with trivalent rare earth metal cations - was synthesized. The rare earth tetracyanidoborates form isostructural groups, e.g. [LRE(H2O)5][B(CN)4]3•0.5 H2O, with LRE3+ = La, Ce, Pr, Nd, Sm, Eu, Gd and [HRE(H2O)7][B(CN)4]3 with HRE3+ = Tb, Dy, Ho, Er, Tm, Yb, Lu and Y. These tetracyanidoborates exhibit rare earth cation specific luminescence properties which are improved by the tetracyanidoborate anion. Therefore, the tetracyanidoborates with trivalent rare earth metal cations could have possible applications in phosphors.