Tb3+- and Eu3+-doped lanthanum oxysulfide nanocrystals.: Gelatin-templated synthesis and luminescence properties

Tb3+- and Fu(3+)-doped lanthanum oxysulfide nanocrystals (NCs) with homogeneous grain size have been prepared by a gel-network coprecipitation method using gelatin as the template and ammonium sulfate as the sulfurizing agent and a following reduction process at relatively low temperatures (750 degrees C) in a H-2 atmosphere. The products were characterized using thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffractometry (XRD), and transmission electron microscopy (TEM). The gelatin template can act as a "nanoreactor", which is beneficial to the dispersion and size control of the coprecipitation product. The high decomposition temperature (about 482 degrees C) of the gelatin network is advantageous to prevent aggregation of the newly formed (LaO)(2)SO4 NCs during calcination of the coprecipitation product. Single hexagonal phase La2O2S NCs were obtained by reduction of the (LaO)(2)SO4 powder, and the NCs are equiaxial in shape with particle sizes ranging from 40 to 50 urn. The photoluminescence spectra and time-resolved spectra of the La2O2S:Tb(FU) in phosphate buffer were investigated. The results show that the La2O2S:Tb NCs have a strong luminescence at 544 run, whose intensity decreases along with decreasing particle size. Concentration quenching occurs when the Tb concentration reaches 8 mol %. The fluorescence color of the La2O2S:Eu NCs depends on the concentration of Eu3+ ions. The red emission (at 625 nm) from D-5(0) transition has a much longer decay time than the green emission from ID, transition of the La2O2S:Eu NCs. The Tb3+- and the Eu3+-doped La2O2S NCs have respective fluorescence lifetimes of 1.10 and 0.41 ms in phosphate buffer, allowing their potential applications in biological labeling.