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

Abstract

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 at 581 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 Sm2+ 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. CdSe and CdSe:Sm NCs were prepared via a water phase method. The structure and optical properties were investigated; the Sm2+ was doped into CdSe NCs successfully. CdSe and CdSe:Sm NCs all exhibit nearly spherical particles, doping Sm2+ increases the particle size, and the QYs are also enhanced. As the reaction time varies to 1, 2, 5, 8 and 10 h, the emission spectra of CdSe NCs present redshift, while the CdSe:Sm NCs have a fixed emission peak, which is the characteristic peak of Sm2+. As compared with pure CdSe NCs, the emission spectra of CdSe:Sm NCs appear blueshift by 20–36 nm. Doping Sm2+ into CdSe NCs can improve the optical properties.