Photoluminescence studies of ThO2 : Eu3+ nanopowders

Eu3+ doped ThO2 nanopowders were prepared by urea combustion route. The PL spectra of these samples showed an intense emission at 588 nm along with weak ones at 604 and 627 nm. Nanopowders obtained via annealing at different temperatures in the range 300-900 deg C had given identical emission spectra typical of Eu3+ at cubic site. On annealing at 300 deg C Eu3+ ions were incorporated at the cubic site in ThO2 lattice and showed the formation of ThO2. The changes in intensity ratio of [5Do-7F2/5 Do-7F1 ] transitions on annealing had given evidence for loss of symmetry with decrease in particle size. Excitation spectra consisted of a Band Edge(Be) peak around 208 nm along with a Charge Transfer Band (CTB) around 258nm. On annealing blue shift in BE peak and red shift in CTB was observed due to reduced particle size at lower temperatures. (author)