Rapid annealing: A novel processing technique for Cr:ZnAl2O4 nanoparticles

Nanocrystalline Cr: ZnAl2O4 was synthesized for the first time by rapid thermal annealing the corresponding hydroxide precipitate in just 10 min. The XRD patterns showed that synthesis between 500 degrees C and 700 degrees C had smaller crystallites (similar to 2.4 - 4 nm), while at 800 degrees C and 900 degrees C, had similar to 10 nm crystallites. HRTEM images of the 900 degrees C sample showed the well-developed lattice fringes confirming the high crystallinity. The particles were polyhedral having an average size of similar to 16 nm. The diffuse reflectance spectra showed characteristic (4)A(2g) -> T-4(1g) and (4)A(2g) -> T-4(2g) transitions, while the photoluminescence emission spectrum comprised of the zero phonon line (R-line) along with other multi-phonon side bands that are characteristic of the spin - parity forbidden transitions of the Cr3+ ion. The emission spectra and photoluminescence lifetimes are comparable with reports on sensing and imaging applications. Our work demonstrates the suitability of this technique to quickly synthesise phosphors for a variety of applications. (C) 2017 Elsevier B. V. All rights reserved.