title: Preparation and surface effect analysis of trivalent europium-doped nanocrystalline La2O2S.
abstract: La2O2S:Eu3+ nanocrystals (NCs) with a mean size of 18 nm are prepared by gel thermolysis. The morphology of the particles is hexagonal. The surface Eu3+ ions are first detected by time-resolved spectra in the 5D0 --> 7F1 region. Because the symmetry of the sites occupied by surface Eu3+ ions is lower, the 5D0 --> 7F1(E) line, which is doubly degenerate in the bulk crystal, is split, and the fluorescence lifetime becomes shorter. The results of the laser-selective excitation indicate that the degradation of the site symmetry of Eu3+ seems to be abrupt, which means the as-synthesized La2O2S:Eu3+ NCs might be of the La2O2S/La2O(2-x)S(1+x)core-shell structure and the shell are not in a disordered state but a rather pure one.
authors.affiliation: Institute of Optoelectronic Technology, Beijing Jiaotong University, 100044 Beijing, China. hillphs@sina.com
authors.forename: Hongshang
authors.initials: H
authors.lastname: Peng
authors.forename: Shihua
authors.initials: S
authors.lastname: Huang
authors.forename: Fangtian
authors.initials: F
authors.lastname: You
authors.forename: Jianjun
authors.initials: J
authors.lastname: Chang
authors.forename: Shaozhe
authors.initials: S
authors.lastname: Lu
authors.forename: Lin
authors.initials: L
authors.lastname: Cao