Colloidal CuFeS₂ Nanocrystals: Intermediate Fe d-Band Leads to High Photothermal Conversion Efficiency

Abstract

We describe the colloidal hot-injection synthesis of phase-pure nanocrystals (NCs) of a highly abundant mineral, chalcopyrite (CuFeS2). Absorption bands centered at around 480 and 950 nm, spanning almost the entire visible and near-infrared regions, encompass their optical extinction characteristics. These peaks are ascribable to electronic transitions from the valence band (VB) to the empty intermediate band (IB), located in the fundamental gap and mainly composed of Fe 3d orbitals. Laser-irradiation (at 808 nm) of an aqueous suspension of CuFeS2 NCs exhibited significant heating, with a photothermal conversion efficiency of 49%. Such efficient heating is ascribable to the carrier relaxation within the broad IB band (owing to the indirect VB–IB gap), as corroborated by transient absorption measurements. The intense absorption and high photothermal transduction efficiency (PTE) of these NCs in the so-called biological window (650–900 nm) make them suitable for photothermal therapy as demonstrated by tumor cell annihilation upon laser irradiation. The otherwise harmless nature of these NCs in dark conditions was confirmed by in vitro toxicity tests on two different cell lines. The presence of the deep Fe levels constituting the IB is the origin of such enhanced PTE, which can be used to design other high performing NC photothermal agents.

Cu5FeS4 Nanoparticles With Tunable Plasmon Resonances for Efficient Photothermal Therapy of Cancers

“…The optical absorption spectrum of CFS nanoparticles, obtained from the reaction with a ratio of 20% for iron source to copper source, showed a peak around 1,100 nm. The NIR absorption may be attributed to 3d electronic transitions from the valence band to an intermediate band, similar to CuFeS 2 nanocrystals (Ghosh et al, 2016) and CuCo 2 S 4 nanocrystals (Li et al, 2017). The ratio of Cu to Fe was found to be 4.99, confirmed by ICP-AES.…”

Doping and Surface Effects of CuFeS2 Nanocrystals Used in Thermoelectric Nanocomposites

“…This size range is difficult to achieve as steric stabilization in organic solvents is generally limited to crystal sizes below 20 nm . Therefore, the CuFeS 2 NC synthesis methods described in the literature produce much smaller sizes in the range of 3–15 nm ,,. In view of the fabrication of thermoelectric pellets, the synthesis is scaled up to the gram scale, i. e. to significantly higher quantities than those obtained with standard colloidal syntheses .…”

Copper Iron Sulfide Nanocrystal‐Bulk Silicon Heterojunctions for Broadband Photodetection

“…While Si has been used for visible (400–1100 nm) detectors, [ 13 ] CuFeS 2 has the potential for sensing a significantly broader 300–2500 nm wavelength window. [ 14–17 ] Unlike their constituent semiconductors, CuFeS 2 /Si heterojunctions sense radiation not just till 2500 nm, but also to wavelengths below the bandgap of either constituent through a slower photothermal response. We associate a heat capacity of 1.5 J K −1 at room temperature with typical devices and a dark current that varies as 0.7 µA K −1 at room temperature.…”