Soft synthesis and vacuum ultraviolet spectra of YAG:Ce3+ nanocrystals:: reassignment of Ce3+ energy levels

Ce3+-doped YAG nanoparticles have been synthesized at relatively low temperatures by the co-precipitation and polymer-assisted sol-gel methods and characterized by Fourier transform infrared spectroscopy (FT-IR), x-ray diffraction (XRD) and x-ray absorption near-edge structure (XANES) measurements. Calcination of the product was carried out at temperatures between 800 and 1100 degrees C. Products calcined at the lower temperature contained a greater proportion of Ce4+, and this contributed in part to the lower intensity of the characteristic yellow photoluminescence. The synchrotron radiation excitation spectrum of this yellow emission band exhibits bands due to Ce3+ absorption as well as the host band gap. The origin of a luminescence band at about 300 nm obtained under band- gap excitation is discussed. Previous assignments of the 5d electronic energies in YAG: Ce3+ are critically assessed, and in the light of the new energy level and transition intensity calculations a revised assignment is put forward for the 5d energy levels.