β-LaTeBO5 and RETeBO5 (RE = Y, Gd, Tb): explorations of new optical materials in the RE(iii)–Te(iv)–B–O system

Four novel crystals of the RE( iii )–Te( iv )–B–O system (β-LaTeBO 5 and RETeBO 5 (RE = Y, Gd, Tb)) have been obtained, which exhibit wide transparency (0.4–6.5 μm), large birefringence and high thermal stability.