Quantum Optoelectronics

Abstract:

We demonstrate that semiconductor quantum dots can be excited efficiently in a resonant three-photon process, whilst resonant two-photon excitation is highly suppressed. Time-dependent Floquet theory is used to quantify the strength of the multi-photon processes and model the experimental results. The efficiency of these transitions can be drawn directly from parity considerations in the electron and hole wavefunctions in semiconductor quantum dots. Finally, we exploit this technique to probe intrinsic properties of InGaN quantum dots. In contrast to non-resonant excitation, slow relaxation of charge carriers is avoided which allows us to measure directly the radiative lifetime of the lowest energy exciton states. Since the emission energy is detuned far from the resonant driving laser field, polarization filtering is not required and emission with a greater degree of linear polarization is observed compared to non-resonant excitation.

Abstract:

The main challenges in the optical and morphological tuning of highly stable orange-emitting Mn-doped perovskite include achieving uniform dopant distribution, maintaining structural integrity under varying environmental conditions, and optimizing luminescent efficiency while minimizing non-radiative recombination pathways. This study presents a novel, one-step, water-induced ultrafast synthesis strategy for obtaining Mn-doped mixed-halide perovskites at room temperature. This technique offers morphological control by varying the amount of water-based precursor, allowing the tuning of resulting nanostructures to produce nanoplatelets, nanocubes, or nanowires. In the growth mechanism, Mn2+ dopants affect the crystal structure by promoting stable growth and uniform doping at higher concentrations, while water improves ion dispersion, reaction kinetics, and passivation, facilitating optimal crystal growth and the formation of desired nanostructure morphologies. The synthesized Mn:CsPbBr3−xClx NCs form a highly stable colloidal solution with approximately 100 % emission stability for up to one year under ambient conditions and retain 98.9 % of its photoluminescence after aging at 85 °C for 200 h. We also explore the PL mechanism in Mn:CsPbBr3-xClx NCs, where temperature-dependent PL analysis reveals energy transfer from CsPbBr3-xClx exciton states to Mn2+-doped levels, enhancing PL intensity, with both exciton and Mn2+ emissions exhibiting a blue shift as the temperature increased from 6 K to 300 K, attributed to lattice expansion and electron–phonon interactions. A warm white light emission is achieved with excellent stability and an exceptionally wide color gamut coverage. The proposed strategy has the potential to enable large-scale synthesis and fabrication of highly stable perovskite devices for high-quality display and lighting applications.

Abstract:

The miniaturization and enhanced functionality of LiDAR systems present critical challenges in automotive sensing technologies, particularly in achieving efficient wide-angle beam scanning while maintaining compact form factors. We demonstrate a novel dual-wavelength polarization-selective concave metalens operating at 904 nm and 940 nm wavelengths, the standard operating wavelengths for LiDAR systems. By engineering rectangular TiO2 nanopillars on a quartz substrate, we achieved simultaneous polarization filtering and concave phase profile functionality within a single metasurface layer. The optimized 600 nm × 600 nm unit cell design with 1.7 μm height nanopillars enables full 2π phase coverage while maintaining high transmission efficiency for the desired polarization state. Our fabricated metalens exhibits remarkable polarization extinction ratios (ER) of 124:1 and 102:1 at 904 nm and 940 nm wavelengths, respectively. Angular-resolved measurements demonstrate wide beam divergence angles of 148° and 138° at the respective wavelengths, with 50 % of total power contained within ± 38° and ± 25°.

Abstract:

Achieving efficient optical coupling between the emission from perovskite quantum dots (PQDs) and photonic integrated elements requires ultranarrow linewidths and highly directional emission. These are challenging goals at room temperature due to the broad and isotropic nature of perovskite emission. Here, we demonstrate ultranarrow‐linewidth emission from CsPbBr3 PQDs at room temperature, in both spontaneous and stimulated regimes, by coupling to state‐of‐the‐art open‐access curved dielectric cavities under continuous wave excitation. The emission is confined to a single transverse electromagnetic mode of the cavity, achieving a remarkably narrow linewidth of 0.2 nm, ≈100× narrower than free‐space emission in both the emission regime. Single‐mode lasing from a small number of PQDs is observed, yielding a quality factor of ≈2590, among the highest reported for single‐mode lasing. The open‐access design enables precise tuning of cavity length and selective coupling of emitters in their native state, overcoming the limitations associated with closed and fixed‐length vertical‐cavity surface emitting laser geometries. The geometry's low divergence and tunability provide an efficient route for integrating perovskite emitters with on‐chip photonic circuits, advancing their use in quantum and optoelectronic technologies. Continuous‐wave lasing from a small number of perovskite quantum dots is achieved by coupling their photoluminescence to open‐access curved dielectric cavities. This geometry confines their emission into a single optical mode, sharply narrowing linewidths in both spontaneous and lasing regimes. Tunable cavity spacing enables precise mode control and high‐Q single‐mode lasing with low divergence emission.

Abstract:

We report the fabrication of nanoscale MoS2 (nMoS2) via laser ablation in liquid and its application in electrochemical sensing. The laser ablation process fragments microscale MoS2 sheets into ~5 nm dots with stable aqueous dispersibility. Electrochemical analysis reveals that nMoS2 possesses multiple reversible redox states, enabling it to participate in redox cycling reactions that can amplify electrochemical signals. When the nMoS2 is embedded in an electrochemically inert matrix, a chitosan layer, and subsequently incorporated within a nanostructured Au electrode, the nMoS2-participating redox cycling reactions are further enhanced by the nanoconfinement effect, leading to synergistic signal amplification. As a model system, this hybrid nMoS2-in-nanoporous Au electrode demonstrates a 9-fold increase in sensitivity for detecting pyocyanin, a biomarker of Pseudomonas aeruginosa infection, compared with a flat electrode without nMoS2 loading. This study not only elucidates the redox characteristics of laser-fabricated zero-dimensional transition metal dichalcogenides but also presents a strategy to integrate semiconducting nanomaterials with metallic nanostructures for high-performance electrochemical sensing.