Homogeneously Alloyed CdS_xSe_1-x Nanocrystals:  Synthesis, Characterization, and Composition/Size-Dependent Band Gap

Abstract

Alloy nanocrystals provide an additional degree of freedom in selecting desirable properties for nanoscale engineering because their physical and optical properties depend on both size and composition. We report the pyrolytic synthesis of homogeneously alloyed CdS(x)Se(1-x) nanocrystals in all proportions. The nanocrystals are characterized using UV-visible absorption spectroscopy, transmission electron microscopy, X-ray diffractrometry, and Rutherford backscattering spectrometry to determine precisely structure, size, and composition. The dependence of band gap on nanocrystal size and composition is elucidated, yielding a bowing constant of 0.29, in agreement with bulk values. In addition, the morphology of the resultant nanocrystals can be altered by changing the reaction conditions, generating structures ranging from homogeneous, spherical nanocrystals to one-dimensional gradient nanorods.

Design of cadmium-free colloidal II–VI semiconductor quantum dots exhibiting RGB emission

“…37,38 The calculated curves (solid lines) agree well with the experimentally observed data (dots). Differences between the observed and calculated data were less than, or comparable to, ∼100 meV.…”

“…In general highly monodisperse colloidal QDs are easier to synthesize with diameters in the range of 3-6 nm. [37][38][39][40] This suggests that the target compositions for Zn(Te 1 x Se x ) alloyed QDs are 0.02≤x≤0.68 for green emission and 0≤x≤0.06 and 0.66≤x≤0.9 for blue emission. In the Zn(Te 1 x S x ) alloy system, those are 0.26≤x≤0.37 for red emission, 0.01≤x≤0.2 and 0.45≤x≤0.61 for green emission and 0≤x≤0.02 and 0.63≤x≤0.72 for blue emission.…”

“…Thus, we first evaluated the applicability of the finite-depth-well EMA calculation to alloyed QDs based on a comparison of the calculated optical gap with that experimentally observed for Cd(Se 1 x S x ) 37,38 and Cd(Te 1 x Se x ) 39,40 alloy systems; these two systems are chosen as typical systems that exhibit small and large band gap bowing, respectively. The size and composition dependent optical gap of Zn(Te 1 x Se x ) and Zn(Te 1 x S x ) alloy systems were then calculated.…”

Colloidal Cu2−x(SySe1−y) alloy nanocrystals with controllable crystal phase: synthesis, plasmonic properties, cation exchange and electrochemical lithiation

“…3,5 As an additional degree of freedom in varying the chemical composition of chalcogenide-based materials, more than one chalcogenide species can be present in the lattice, for example S and Se. To date, several colloidal NCs of mixed metal ''sulfides-selenides'' have been reported, for example HgS y Se 1Ày , 6 ZnS y Se 1Ày , 7 SnS y Se 1Ày , 8 CdS y Se 1Ày , 9 PbS y Se 1Ày , 10 CuIn-(S y Se 1Ày ) 2 , 11 Cu x Fe 4 Sn 12 (S y Se 1Ày ) 32 12 and Cu 2 ZnSn(S y Se 1Ày ) 4 . 13 On the other hand, the ability to control the crystal phase and to obtain NCs in phases that were previously non-accessible is also quite relevant (see for example recent works on wurtzite Cu 2 ZnSnSe 4 and Cu 2 ZnSnS 4 NCs).…”

Developing a facile method for highly luminescent colloidal CdSxSe1−x ternary nanoalloys

“…Swafford et al reported that the composition of the CdS x Se 1Àx nanoalloys remained reasonably constant over the growth period for all the Se : S ratios, establishing the homogenous nanoalloy. 12 Ouyang et al also suggested the formation of the homogenous nanoalloys.…”