Photoluminescence properties of Ba3B′B″2O9 (B′=Mg, Co or Zn and B″=Nb or Ta) ceramics with perovskite structure

Optical properties of near-stoichiometric compositions of Ba3B′B″2O9 (B′=Mg, Co or Zn and B″=Nb or Ta) perovskite type materials were studied by means of photoluminescence (PL) spectroscopy. Ba3B′B″2O9 perovskites belong to the family of perovskite materials that exhibit phase transition from a completely disordered system having space group Pm-3m to a 1:2 ordered one with space group P-3m1. As revealed by X-ray diffraction, deviation from stoichiometry results in the formation of Ba- and Nb-rich phases. Photoluminescence measurements demonstrated the presence of two broad peaks, the position of which depends on secondary phase formation: the first one, attributed to the disordered Pm-3m phase, is positioned at approximately 430nm and the second band, positioned at lower energies (i.e., longer wavelengths, around 900nm), was ascribed to the formation of the 1:2 ordered P-3m1 phase. The position of the first peak is influenced by the bond network through distortions in the local environment caused by the specific electronic structure of the B′ cation.