Electronic properties and third-order optical nonlinearities in tetragonal chalcopyrite AgInS₂, AgInS₂/ZnS and cubic spinel AgIn₅S₈, AgIn₅S₈/ZnS quantum dots

Abstract

Comprehensive studies on the electronic properties and spectral dependencies of the third-order nonlinear optical properties of quantum-confined tetragonal chalcopyrite AgInS 2 and its non-stoichiometric cubic spinel AgIn 5 S 8 with reference to their corresponding Zn 2+ alloyed compounds i.e. AgInS 2 /ZnS and AgIn 5 S 8 / ZnS are presented in this work. Nonlinear refraction and nonlinear absorption in the quantum-confined nanocrystals were measured in a wide range of wavelengths (550-1200 nm) using the Z-scan technique.The results revealed the presence of strong two-photon absorption bands in the near-infrared range for both compounds. The impact of Zn 2+ ion alloying was also investigated for both compounds revealing a significant increase of the cubic nonlinearity for the chalcopyrite quantum dots and a negligible change for the spinel-like quantum dots which was discussed as a consequence of different surface reconstruction mechanisms of the tetragonal and cubic nanocrystals. The cubic nonlinearity of the quantum dots is discussed in terms of electronic properties and linear dielectric function dispersions of both systems obtained within the density functional theory. Kinetics of the two-photon excited state recombination was investigated with the femtosecond time-resolved photoluminescence spectroscopy revealing the complex character of electronic relaxation in both systems. The results indicate that the optical properties of the tetragonal AgInS 2 and cubic AgIn 5 S 8 quantum dots are much better suited for the steady-state as well as time-resolved multiphoton fluorescence techniques utilized commonly for bio-sensing applications than their CuIn x S y homologues.

Colorectal Cancer Diagnosis Using Enzyme‐Sensitive Ratiometric Fluorescence Dye and Antibody–Quantum Dot Conjugates for Multiplexed Detection

“…An excitation of 780 nm was used to visualize the tissue architectures by autofluorescence, and the morphologies of the disordered tumor colon tissue and the shapes of cells were visualized (Figure c). The two‐photon cross section of our AgInS 2 /ZnS QD is ≈500 GM at 980 nm which was used for excitation . Some scattered cells were brightly visualized under both autofluorescence and QD imaging.…”

Nonlinear Optical Properties of Emerging Nano‐ and Microcrystalline Materials

“…The third-order nonlinear optical response of the AgInS 2 chalcopyrite (d = 2.8 nm) and non-stoichiometric spinel AgIn 5 S 8 QDs (d = 2.53 nm) were measured in a wide range of wavelengths (550-1200 nm) using the Z-scan technique. [102] The two-photon absorption cross-sections of those nanocrystalline materials were characterized to be 3160 GM for AgInS 2 and 1770 GM for AgIn 5 S 8 at 675 nm, indicating that NLO properties of such quantum dots make them potentially suitable candidates for two-photon fluorescent bioprobes. An enhancement of twophoton excited fluorescence efficiency and low threshold twophoton pumped amplification of spontaneous emission by a strategy of Zn processing onto CuInS 2 (CIS) QDs was presented recently.…”

Influence of Hydrophilic Thiol Ligands of Varying Denticity on the Luminescence Properties and Colloidal Stability of Quaternary Semiconductor Nanocrystals

“…17,18 The optical properties of ternary and quaternary QDs depend on size and chemical composition and differ in many aspects from those of binary II−VI, III−V, and IV−VI QDs. 19,20 While high-quality binary QDs exhibit relatively narrow and symmetrically shaped emission bands and lifetimes in the shorter nanosecond range, AIS, CIS, and ZAIS QDs show broad PL bands, large Stokes shifts, and PL lifetimes of a few hundred nanoseconds, which indicate the involvement of intragap levels in their PL. 10,11,21 The PL features of the latter QDs have been explained by different PL mechanisms such as the radiative recombination of donor−acceptor pairs (DAP) or the selftrapped exciton model (STE), which describes the recombination of a localized hole with a conduction band electron, or a combination of these mechanisms.…”