Electronic Structure Insights into the Tunable Luminescence of CuAl_xFe_1–xS₂/ZnS Nanocrystals

Abstract

We describe the electronic structure and spectroscopic properties of CuAl x Fe1–x S2 nanocrystals and their core/shell structures. The as-synthesized CuAl x Fe1–x S2 core exhibits a tetragonal chalcopyrite structure. The core material exhibits tunable band gap that spans the entire visible to near-infrared spectrum, from 3.48 to 0.53 eV. This tunability is achieved by varying the mole fraction of aluminum and iron from 1:0 to 0:1. The band gap variation with composition deviates from Vegard’s law and corresponds to a bowing coefficient of 1.59 eV. Our observations are interpreted using density functional theoretical calculations. In particular, we find that the significant bowing is well accounted for through significant localization of the Fe electronic states. Most significantly, CuAl x Fe1–x S2 shows photoluminescence upon making a shell of zinc sulfide, which is tunable from 400 to 1400 nm (3.1 to 0.89 eV). CuAl x Fe1–x S2/ZnS are until date the only visible-infrared tunable nanocrystal fluorophore composed entirely of earth abundant elements with atomic numbers 30 and lower.

Copper Iron Chalcogenide Semiconductor Nanocrystals in Energy and Optoelectronics Applications—State of the Art, Challenges, and Future Potential

“…For example, CuFeS x Se 2− x NCs have an SPR band at 408 nm (Figure 3e) [ 66 ] and CuAl x Fe 1− x S 2 at 480 nm (Figure 3f). [ 67 ] Further studies also indicate that the plasmon in these materials is quite stable and inert to different stoichiometric changes in the NCs. Very recently, Cu 3 VS 4 (sulvanite) NCs have shown similar but multiple SPR bands in the visible range.…”

“…f) Absorption spectra of CuAl x Fe 1−x S 2 nanoparticles versus the Al/Fe ratios. Reproduced with permission [67]. Copyright 2016, American Chemical Society.…”

Electronic Structure and Spectroscopy of I–III–VI2 Nanocrystals: A Perspective

“…Besides the success of colloidal approaches to CuFeS 2 NC synthesis, researchers have also successfully employed milling and microwave to produce CuFeS 2 NCs. , In particular, Kumar et al were able to demonstrate NIR photodetection in microwave CuFeS 2 NC/ZnO oxide hybrids . Other iron-based I–III–VI 2 NCs such as CuFeSe 2 NCs also demonstrate a similar set of optical and optoelectronic properties. − The availability of a wide library of I–III–VI 2 semiconductors with narrow band gaps and a well-defined composition could in principle reduce the reliance on alloying and quantum confinement based strategies that need to be pursued in the case of HgTe-based materials. − Phototdetector devices directly relying on sintered I–III–VI 2 inks could thus present significant advantages in the future.…”

The Presence of Charge Transfer Defect Complexes in Intermediate Band CuAl1−pFepS2

“…Recently, Yadav et al demonstrated the ability to synthesise quaternary earth-abundant CuAl x Fe 1−x S 2 nanocrystals with a band gap that is tunable across the entire UV/vis/NIR spectrum, whilst maintaining the chalcopyrite crystal structure [45]. As part of this work, they performed a limited DFT investigation into the electronic structure of the CuAl x Fe 1−x S 2 system showing the projected density of states (PDOS) calculated for the CuAl 0.75 Fe 0.25 S 2 system, the composition of which was obtained by substituting two Al 3+ ions with Fe 3+ ions, i.e., by introducing two [Fe Al ] 0 antisite defects.…”