Synthesis and fluorescence properties of CdTe:Eu3+ nanocrystals and core-shell SiO2-coated CdTe:Eu3+ nanospheres

Eu3+ doped-CdTe(CdTe:Eu3+)nanocrystals were prepared via a facile hydrothermal method,and Eu3+ was successfully incorporated into the crystal lattice of CdTe and measured by X-ray powder diffraction(XRD),transmission electron microscopy(TEM),ultraviolet-visible(UV-Vis) absorption spectroscopy and fluorescence emission.The CdTe:Eu^3+ nanocrystals still have a cubic crystal structure,and the corresponding XRD peaks of CdTe:Eu3+nanocrystals shift to larger angles compared with those of pure CdTe.The CdTe:Eu3+ nanocrystals are monodisperse and the particles size is about 2-4 nm.Compared with pure CdTe,the CdTe:Eu^3+ nanocrystals have larger band gap and thus exhibit blueshift in the emission spectra,which could be accounted for by the energy transfer between Eu^3+ and CdTe.To enhance the stability and functionality of CdTe:Eu3+nanocrystals,the CdTe:Eu3+nanocrystals were coated with SiO2 and the core-shell SiO2-coated CdTe:Eu3+nanocrystals(CdTe:Eu^3+@SiO2) were prepared via microemulsion method.TEM results show that CdTe:Eu3+nanocrystals are uniformly dispersed in the shell,and CdTe:Eu3+@SiO2 nanospheres are uniformly spherical with an average diameter of about 75 nm.The fluorescence emission of CdTe:Eu3+@SiO2(567 nm) shows a blueshift compared with that of CdTe:Eu^3+nanocrystals(632 nm),possibly because of altered surface properties after SiO2 coating.CdTe:Eu^3+and CdTe:Eu^3+@SiO2 with tunable photoluminescence are potentially useful in fabricating optical and bioimaging devices.

Synthesis,characterization and optical studies on Sm2+-doped CdSe nanocrystals:a blueshift and fixed emission with high quantum yields

CdSe:Sm nanocrystals(NCs) were synthesized by a water phase method,and their structures,shapes and optical properties were further characterized.X-ray diffraction(XRD) analysis suggested that both the CdSe and CdSe:Sm NCs contained(111),(220) and(311) lattice planes in the zinc blende structure overlapped with the(002),(110) and(112) lattice planes in the wurtzite structure,and the diameters were about 4.2,3.3 and 2.3 nm for CdSe,CdSe:Sm(8%) and CdSe:Sm(10%) NCs,respectively.All of the CdSe:Sm NCs were monodispersed and uniform spherical nanocrystals.The CdSe:Sm(10%) NCs prepared with different reaction times exhibited constant absorption spectra at 430 nm and a fixed emission peak at581 nm.Compared with those of pure CdSe NCs,the fluorescence emission of CdSe:Sm(10%) NCs blueshifted 20-36 nm,and the absorption peak initially redshifted and then blueshifted with the prolongation of reaction time.In addition,the Sm^2+ doping decreased the fluorescence lifetime and increased the quantum yields(QYs) of CdSe NCs.The QYs of CdSe:Sm NCs increased initially and then decreased with the increase in the amount of doped Sm2+.The initial pH and charge compensator concentration also exhibited significantly enhanced fluorescence emission of CdSe:Sm NCs.