Quantum dots are becoming more recognized as a tool to use in varying photonic and sensing technologies. When quantum dots are illuminated, they can emit light; by altering the quantum dot characteristics, the wavelength of the emitted light can be finely tuned. The emitted light of quantum dots may gradually increase in intensity when continuously illuminated, a behavior of quantum dots called photobrightening. We focus on this brightening behavior and explore different factors that contribute to quantum dot photobrightening. Increased excitation of the quantum dots results in increased rate of photobrightening, shown in this work by exciting quantum dot samples with different laser intensities. By adding plasmonic nanostructures, the excitation light to the quantum dots is enhanced, which also increases the rate of photobrightening. By combining gold nanoparticles with cadmium selenide quantum dots, we determined that gold nanoparticles enhance QD photobrightening by a significant factor, potentially leading to more efficient quantum dot technologies.
This study explores optical characteristics in quantum dots. CdSe quantum dots samples have been prepared and an optical photoluminescence experimental setup has been created to measure the light emission from the quantum dots as a function of time and laser intensity. Initial baseline measurements and photoluminescence spectrum has been measured. This preliminary work sets up future studies of quantum dot photobrightening, which is when the emitted light from a CdSe quantum dots gradually increases with time while under constant laser illumination. Future work will investigate photobrightening as a function of laser intensity and with the presence of plasmonic nanoparticles to give insight into plasmonic enhancement and light interaction between plasmonic particles, quantum dots, and photobrightening effects. Results of this study can add value to future quantum dot technologies.
Localized surface plasmons have been reported for periodic 2D monolayer black phosphorene (BP) nanoribbons in the infrared region. The anisotropic nature of BP causes different plasmonic effects depending on their orientation over select dielectric substrates, leading to tunability and promising future applications in imaging and other detectors. Computational models are used to demonstrate that by tuning the localized plasmonic resonance, as well as the orientation of the BP nanoribbon, it is possible to obtain desired coupled resonance modes and enhanced absorption capabilities. The modes obtained from the absorption spectra span the infrared range and extend our understanding of BP plasmons.
Plasmonic nanodevices are metallic structures that exhibit plasmonic effects when exposed to light, causing scattering and enhancement of that light. These plasmons makes it possible for light to be focused below the diffraction limit. Dark-field spectroscopy has been used to capture the scattering spectra of these structures in order to examine the scattering and resonant frequencies of the plasmons provided by the devices. The geometries of the devices change which wavelengths of light are most readily able to couple to the device, resulting in a change in the wavelength of the scattered light. A variety of device geometries and configurations will be studied, including nanodiscs, nanowires, and plasmonic gratings, along with double-width nanogap plasmonic gratings. These new structures will have features below the fabrication limit of electron-beam lithography, i.e. sub-10 nanometer features. The polarization dependencies of these resonance modes are investigated as well. A relation between device geometry and wavelength will be drawn; in effect, this will allow the selection of geometry of the fabricated device based on the desired wavelength of light to be scattered. Preliminary Raman spectroscopy will also be performed in order to study the device response and usefulness for surface-enhanced Raman spectroscopy.
This work investigates colloidal, semiconductor Cadmium Selenide (CdSe) QDs with optical spectroscopy measurements. A custom-built microscope has been used for photoluminescence spectroscopy and has collected images, videos, and spectra of samples to study the effects of substrates, sample density, uniformity, and QD aging with time. This set up will be used to detect single to a few molecules, shown by fluorescent intermittency, or QD blinking. Differences in the spectrum will be noted as related to the age of samples, the density of the quantum dots, and the concentration of samples. Further experiments include the potential plasmonic enhancement of QD photoluminescence by gold nanoparticles or nanostructures.
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