New ultraviolet B emission from gadolinium activated BaZrO 3 phosphor - An electron paramagnetic resonance and optical study

Gadolinium activated BaZrO3 phosphor has been prepared by the solution combustion method. Powder X-ray diffraction and scanning electron microscopy methods are used to characterize the prepared phosphor. Electron paramagnetic resonance (EPR) spectra of un-doped and gadolinium activated BaZrO3 phosphor has been studied. Pure BaZrO3 exhibits an EPR spectrum which is a superposition of spectra from two distinct centers. One of the centers (center I) with an isotropic g factor 2.0016 is tentatively assigned to an F+-type center (singly ionized oxygen vacancy). Center II with an axially symmetric g-tensor with principal values g(parallel to) = 1.955 and g(perpendicular to) = 1.973 is identified as a Zr3+ ion. The EPR spectrum of gadolinium activated BaZrO3 samples exhibit resonance signals with the effective g values at g approximate to 1.94 and g approximate to 4.10. The signal at g approximate to 1.94 has been attributed to Gd3+ ions disposed in a weak cubic symmetry field between the Gd3+ ion and the phosphor lattice. The excitation spectrum exhibits a dominant band with a maximum at 275 nm (36364 cm(-1)). Upon excitation at 275 nm (36364 cm(-1)), the emission spectrum exhibits a well defined ultraviolet B emission band with a maximum at 314 nm (31847 cm(-1)) corresponding to P-6(7/2) -> S-8(7/2) transition. (C) 2015 Elsevier B.V. All rights reserved.