Structural phase transitions and photoluminescence properties of Eu(3+) doped Ca(2-x)BaxLaNbO6 phosphors.

Crystal structures of the series of double perovskites Ca(2-x)BaxLaNbO6:Eu(3+) phosphors have been examined by powder X-ray diffraction and Rietveld refinements. Ca2LaNbO6 has a monoclinic (P21/n) and Ba2LaNbO6 has a monoclinic (C2/m) structure. The structural phases of Ca(2-x)BaxLaNbO6:Eu(3+) samples are divided into three sections depending on different Ca/Ba ratios: (1) monoclinic phase (P21/n) as Ca2LaNbO6 in the range of x = 0-0.1, (2) mixed phases containing Ca2LaNbO6 and Ba2LaNbO6 between 0.15 and 1.2, and (3) monoclinic phase (C2/m) as Ba2LaNbO6 for x = 1.4-2. Eu(3+) ions act as the structural probes to study the structural phase transitions, and the evolution of the photoluminescence properties and thermal stability behaviours has been also comparatively investigated depending on different structural symmetries from Ca2LaNbO6 to Ba2LaNbO6 phase. The strong red emission from (5)D0-(7)F2 peaking at 618 nm can be found in Ca2LaNbO6:Eu(3+) phosphors, which is attributed to the low crystal field effect of the activator ions located in the highly distorted [LaO8] polyhedra sites. The composition-optimized phosphors can find applications in white light emitting diodes (LEDs).