Low-cost, environmentally friendly synthesis, structural and spectroscopic properties of Fe:ZnSe colloidal nanocrystals

Abstract

Semiconductor nanocrystals have been the focus of great interest in recent years due to their size dependent physical and chemical properties. Here, we present a facile, eco-friendly and feasible approach for the fabrication of highly luminescent Fe:ZnSe nanocrystals by using low-cost, and environmentally friendly reagents and solvents, benefiting the practical applications. The developed process produces Fe:ZnSe nanocrystals having in situ capping of mercaptoacetic acid on the surface, resulting in good water solubility due to effective surface functionalization. Surface investigation of the nanocrystals indicates that mercaptoacetic acid is chemisorbed onto the surface of Fe:ZnSe nanocrystals and the sulfur atom in the thiol is coordinated to the zinc atom, leading to the formation of the covalent Zn–S bond. Ultra-small Fe:ZnSe nanocrystals were produced with average particles size ca. 4nm, indicating they are in the alleged quantum confinement regime. The Fe:ZnSe samples are found to be nanocrystalline in nature with cubic zinc blende structure. The Fe:ZnSe nanocrystals are quasi-spherical shaped, and the regular behavior of the lattice fringes inside the nanocrystal further demonstrates that most nanoparticles have a good crystalline characteristics with no obvious defects. The microstructural properties of the Fe:ZnSe nanocrystals were probed by X-ray diffraction in detail. The photoluminescence spectrum band is relatively narrow and symmetric, which reveals the obtained Fe:ZnSe nanocrystals are nearly monodisperse and homogeneous. The photoluminescence quantum yield of the fabricated Fe:ZnSe nanocrystals was calculated to be ca. 35%, that makes Fe:ZnSe nanocrystals a promising candidate for applications in biolabeling, bioimaging, and light emitting devices. The blue shifted band gap energy of the fabricated Fe:ZnSe nanocrystals in comparison to the corresponding bulk value derives from size quantization characteristics of the resulting products in nanoparticle form. The exhibited quantum confinement effects were probed within the framework of the effective mass approximation model. Furthermore, the underlying mechanisms were also elucidated. This work provides a more promising synthetic strategy with advantages of being simplicity and low cost in preparation, environmentally friendly and suitable for large scale production of functionalized doped and alloyed nanocrystals with excellent synthetic reproducibility.