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Abstract:

We have estimated the intrinsic complex refractive index spectrum of a CsPbBr3 nanocrystal. With various dilute solutions of CsPbBr3 nanocrystals dissolved in toluene, effective refractive indices were measured at two different wavelengths using Michelson interferometry. Given the effective absorption spectrum of the solution, a full spectrum of the effective refractive index was also obtained through the Kramers–Krönig relations. Based on the Maxwell–Garnett model in the effective medium approximation, the real and imaginary spectrum of the complex refractive index was estimated for the CsPbBr3 nanocrystal, and the dominant inaccuracy was attributed to the size inhomogeneity.

Abstract:

Data for paper on plasmonic enhanced emission from perovskite nanowires

Abstract:

Flexible optoelectronics have broad applications in healthcare and various industries. Unlike traditional (two-dimensional) 2D designs, flexible 3D optical sensors enable advanced functions like light directionality detection, intensity mapping, and velocity measurement. However, their integration with 2D circuit boards adds manufacturing complexity. Solving this could unlock untapped applications in navigation, agriculture, and remote sensing. In this study, selective buckling of flexible circuit boards is investigated to develop an all-in-one flexible (three-dimensional) 3D optical sensor for light detection with high sensitivity to periodic light pulses. By employing a buckling-based design, the developed flexible 3D phototransistor is found to be adjustable for measuring incident light angles between 0° and 87°, with an average error of less than 5°. Additionally, the sensor is able to measure object velocity with a maximum deviation of only 1.5% from the actual speed. In this design, the flexible circuit board is also integrated with Bluetooth Low Energy (BLE) technology to wirelessly transmit readings to a smartphone application to enable efficient data processing, transmission, visualization, and analysis. The platform's effectiveness is then demonstrated for unmanned aeraial vehicles (UAV) navigation and solar tracking, highlighting its strong potential for real-world use in autonomous systems and environmental monitoring.

Abstract:

The optical Aharonov-Bohm effect in a quantum ring was investigated in terms of magnetic field dependence of excitons and biexcitons. The fine exciton states of quantized orbital angular momentum in a quantum ring were considered theoretically, and the presence of quantum beats was predicted as evidence of the quantum coherence of the fine exciton states. In the case of GaAs/GaAlAs quantum rings grown by the droplet epitaxy, we found various disorder effects are associated such as structure anisotropy, localization, and internal electric field, resulting in a modulation of the oscillation periods. Additionally, we found that a strongly correlated exciton pair can be formed in a single quantum ring similar to the Wigner molecule. In this case, the biexciton emission energy changes abruptly at transition magnetic fields with a fractional oscillation period compared to that of the exciton, the so-called fractional optical Aharonov-Bohm oscillations.

Abstract:

The optical properties of graphene (Gr)-covered CsPbBr₃ quantum dots (QDs) were investigated using micro-photoluminescence spectroscopy, revealing a remarkable three orders of magnitude enhancement in photoluminescence (PL) intensity compared to bare CsPbBr₃ QDs. To elucidate the underlying mechanisms, we combined experimental techniques with density functional theory (DFT) calculations. DFT simulations showed that the graphene layer generates interfacial electrostatic potential barriers when in contact with the CsPbBr₃ surface, impeding carrier leakage from perovskite to graphene and enhancing radiative recombination. Additionally, graphene passivates CsPbBr₃ surface defect states, suppressing nonradiative recombination of photo-generated carriers. Our study also revealed that graphene becomes n-doped upon contact with CsPbBr₃ QDs, activating its plasmon mode. This mode resonantly couples with photo-generated excitons in the perovskite. The momentum mismatch between graphene plasmons and free-space photons is resolved through plasmon scattering at Gr/CsPbBr₃ interface corrugations, facilitating the observed super-bright emission. These findings highlight the critical role of graphene as a top contact in dramatically enhancing CsPbBr₃ QDs’ PL. Our work advances the understanding of graphene-perovskite interfaces and opens new avenues for designing high-efficiency optoelectronic devices. The multifaceted enhancement mechanisms uncovered provide valuable insights for future research in nanophotonics and materials science, potentially leading to breakthroughs in light-emitting technologies.