Synthesis and low-order optical nonlinearities of colloidal HgSe quantum dots in the visible and near infrared ranges

Heterojunctions of Mercury Selenide Quantum Dots and Halide Perovskites with High Lattice Matching and Their Photodetection Properties

Heterojunction semiconductors have been extensively applied in various optoelectronic devices due to their unique carrier transport characteristics. However, it is still a challenge to construct heterojunctions based on colloidal quantum dots (CQDs) due to stress and lattice mismatch. Herein, HgSe/CsPbBrxI3-x heterojunctions with type I band alignment are acquired that are derived from minor lattice mismatch (~1.5%) via tuning the ratio of Br and I in halide perovskite. Meanwhile, HgSe CQDs with oleylamine ligands can been exchanged with a halide perovskite precursor, acquiring a smooth and compact quantum dot film. The photoconductive detector based on HgSe/CsPbBrxI3-x heterojunction presents a distinct photoelectric response under an incident light of 630 nm. The work provides a promising strategy to construct CQD-based heterojunctions, simultaneously achieving inorganic ligand exchange, which paves the way to obtain high-performance photodetectors based on CQD heterojunction films.

Optical and structural properties of Sn and Ag-doped PbS/PVA nanocomposites synthesized by chemical bath deposition

In this work, Sn and Ag doped PbS/PVA nanocomposites, in three different concentrations were successfully prepared using the low-cost and simple method of chemical bath deposition (CBD). X-ray diffraction patterns confirmed the formation of the PbS cubic phase in all of the nanocomposites. FE-SEM images showed that PbS NPs are cubic in shape and the doping can alter the shape of grains. DLS analysis applied for solution NPs exhibited a 175 nm size distribution for PbS NPs and decreased by doping Ag and Sn to almost 100 nm and 110 nm, respectively. Optical absorption spectra showed the blue phenomena and the band gaps of Sn: PbS/PVA and Ag: PbS/PVA nanocomposites increased with adding Sn and Ag from 3.08 eV for pure PVA/PbS to 3.33 eV for Sn doped and 3.43 eV for Ag-doped samples. The nonlinear refractive index is decreased from 0.55 m2 W-1 for pure PVA/PbS to 0.11 m2 W-1 and 0.13 m2 W-1 for Sn and Ag-doped samples, respectively. Hence, doping Ag and Sn enhanced the optical sensitivity issue of nanocomposites and raised the optical resistivity. Collectively, our results can be useful in the design of linear and nonlinear optical devices such as sensors and optical switches and limiters.

Investigation of Nonlinear Optical Processes in Mercury Sulfide Quantum Dots

The authors report the third-harmonic generation, nonlinear refraction, and nonlinear absorption in HgS quantum dot (QD) suspensions and films using the nanosecond and femtosecond pulses. High conversion efficiency (7 × 10⁻⁴) towards the third harmonic (TH) of the 900–1700 nm, 150 fs laser in the thin (70 nm) films containing HgS QDs deposited on the glass substrates is obtained. The authors analyze spectral dependencies of the TH, nonlinear refractive indices, and nonlinear absorption coefficients of QDs in the 500–1700 nm range and discuss the relation between the TH process and the low-order nonlinear optical properties of these quantum dots.