Monoclinic (P21/n) structure of B-site ordered double perovskites Ba2R2/3TeO6 (R = Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) is elucidated from XRD, Raman and IR spectroscopy. The maximum relative temperature sensitivity of Ba2Y2/3TeO6:Eu3+ between 300–500 K is 0.18% K−1.