Controlled synthesis and luminance properties of lanthanide-doped β-NaYF_4 microcrystals

Hexagonal yb3＋,Er3＋-doped NaYF4 crystals with different morphologies were synthesized by a facile hydrothermal method at 140-200 ℃. Their shape and size could be controlled by varying hydrothermal temperature, time and doping effect of Ce3＋ ions. Interestingly, the products displayed hexagonal sheet, plate, crown-like prism to tube changes in the temperature range from 140 to 200 ℃. A combination of ＂diffusion-controlled growth＂ and ＂selective adsorption＂ was proposed to understand the formation of the NaYF4 crystals with well-defined shapes. NaYF4：yb3＋/Er3＋ crystals exhibited shape-dependent up-conversion （UC） luminescence under excitation of 980 nm, and their luminescence property could be tuned by doping Ce3＋ ions.

Controlled preparation and self-assembly of NdVO_4 nanocrystals

Phase-pure t-NdVO_4 nanocrystals with different shapes have been synthesized by facile and repeatable hydrothermal methods. The as-synthesized t-NdVO_4 nanoparticles were characterized by various techniques of X-ray diffraction（XRD）. scanning electron microscope（SEM） and transmission electron microscope（TEM）. The growth process and assembly behavior of t-NdVO_4 nanorod arrays were investigated. The results show that the morphology of t-NdV04 nanocrystals is greatly related to the pH value of precursor solution and that strong basic solution is not in favor of the formation of t-NdVO_4 nanoparticles. Due to the strong adhesive action and stabilization of OH^-ions to some crystal faces of NdVO_4, neodymium vanadate crystallite grows into oriented short nanorods and then into nanorod arrays. The shape, crystalline and dimension of NdVO_4 nanocrystals can be effectively governed in our work.

Hydrothermal synthesis and optical properties of Zn_(1-x)Mn_xS nanorods

Zn1-xMnxS （x = 0-0.05） nanorods were successfully synthesized through a hydrothermal route. The morphology, composition and microstructure of Zn1-xMnxS nanorods were characterized respectively by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and Raman spectrometer. The optical properties of Zn1-xMnxS nanorods were determineded by UV-Vis absorption spectroscopy and photo- luminescence （PL） emission spectroscopy. The results show that the introduction of Mn^2＋ on interstitial sites in ZnS lattice has significant influence on the Raman spectra, UV-Vis absorption spectra and PL emis- sion spectra. With the increase of Mn^2＋, the lengths of the sampled nanorods become shorter and the morphologies of the products show disorder accompanied by some nanoparticles. The absorption band edge shifts to longer wavelength. The intensity of the ZnS-related emission gradually becomes weaker, whereas, the Mn^2＋-related broad emission spectra located at 580 nm gradually red-shifts and increases. Occupation of Zn^2＋ sites in the lattice by Mn^2＋ ions results in lattice distortion and influences the energy level structure of ZnS. The Mn doping is found responsible for the changes in the defect-related emission of the ZnS nanorods.