The growing attention to perovskite nanocrystals is connected with their unusual and potentially useful electronic and optical properties. I will discuss the bulk energy band structure of CsPbX3 (X = I, Cl, and Br) perovskites and show that all of them have the band edge at R-point of the Brillouin zone. To describe electronic and optical properties of perovskite nanocrystals we have derived the four band effective mass Hamiltonian, which describes the electronic properties of electron and holes near the band edge. Using this Hamiltonian we calculate the lowest quantum confined levels of electrons and holes and the spectra of the allowed optical transitions. The calculations takes into account the cubic shape of the perovskite nanocrystals, that results into inhomogeneous electric field of emitted and absorb photons. The symmetry of the ground exciton state has been analyzed and the radiative decay time has been calculated. The results of our theoretical calculations have explained 200 ps radiative decay time and polarization properties measured in single CsPb(BrCl2) quantum dot experiments .
KEYWORDS: Energy transfer, Gold, Data modeling, Energy efficiency, Fluorescence resonance energy transfer, Nanocrystals, Metals, Semiconductors, Quantum dots, Nanolithography
We characterize energy transfer between luminescent 1.5 nm diameter gold nanocrystal (AuNC) acceptors and three structurally/functionally-distinct classes of emissive donors including organic dyes, metal chelates and semiconductor quantum dots (QDs). Energy transfer efficiencies within the donor-AuNC assemblies were evaluated with steady-state and time-resolved measurements. Donor quenching was observed for every donor-acceptor pair although AuNC sensitization was only observed from metal-chelates and QDs. Results were analyzed with Förster’s dipole-dipole coupling model (FRET) and dipole-metal damping models including nanosurface energy transfer (NSET) and nanovolume energy transfer (NVET). FRET dramatically underestimated energy transfer efficiencies while the damping models provided qualitatively better fits to the data although neither fully reproduces the experimental data. Analysis suggests that organic dye donor quenching without corresponding AuNC sensitization results from enhanced intersystem crossing between dye singlet and triplet states driven by AuNC magnetic dipoles. We further consider factors that account for the unique electronic properties of the ultra-small luminescent AuNCs including the high excited state densities, rapid dephasing time and strong electron confinement as well as paramagnetic properties. Overall, the results provide insight into requirements necessary for realizing applications based on AuNC acceptor sensitization.
Recent interest in quantum dots (QDs) stems from the plethora of potential applications that arises from their tunable absorption and emission profiles, high absorption cross sections, resistance to photobleaching, functionalizable surfaces, and physical robustness. The emergent use of QDs in biological imaging exploits these and other intrinsic properties. For example, quantum confined Stark effect (QCSE), which describes changes in the photoluminescence (PL) of QDs driven by the application of an electric field, provides an inherent means of detecting changes in electric fields by monitoring QD emission and thus points to a ready mean of imaging membrane potential (and action potentials) in electrically active cells. Here we examine the changing PL of various QDs subjected to electric fields comparable to those found across a cellular membrane. By pairing static and timeresolved PL measurements, we attempt to understand the mechanism driving electric-field-induced PL quenching and ultimately conclude that ionization plays a substantial role in initiating PL changes in systems where QCSE has traditionally been credited. Expanding on these findings, we explore the rapidity of response of the QD PL to applied electric fields and demonstrate changes amply able to capture the millisecond timescale of cellular action potentials.
We have fabricated and studied two-dimensional (2D) and three-dimensional (3D) metallo-dielectric photonic crystals (MDPC) in the visible/near ir spectral range using a variety of optical techniques. The 2D MDPC showed anomalous transmission due to surface plasmon polaritons in resonance with the photoluminescence band of a π-conjugated polymer based on a poly-phenylene-vinylene derivative. Consequently we fabricated an organic light emitting diode (OLED) using the 2D MDPC as a cathode with improved performance over an OLED with unperforated cathode. The 3D MDPCs are based on metal infiltrated opal photonic crystals. We studied the reflectivity spectrum of various metal infiltrated MDPCs and found that the reflectivity is low in the visible spectral range but dramatically increases towards the infrared revealing the elusive metallic gap. Our findings are in good agreement with recent theoretical and numerical calculations based on a commercial program.
The theory of diffraction in the system consisting from the left-handed and the right-handed materials is constructed. The theory is based upon the Huygens principle and the Kirchhoff integral and it is valid if the wavelength is smaller than any relevant length of the system. The theory is applied to the calculation of the smearing of the foci of the Veselago lens due to the finite wavelength. We show that the Veselago lens is a unique optical instrument for the 3D imaging, but it is not a "superlens" as it has been claimed recently. We analyze the possibility of obtaining a left-handed materials on the basis of the metallic photonic crystals. The recent experimental results on the LHM are discussed.
Measurements of the in-plane electron effective mass in GaInAs/InP single quantum wells as a function of well thickness using far-infrared optically detected cyclotron resonance (FIR- ODCR) is reported. The FIR-ODCR technique is described, the mechanism of detection is explained, and the experimental results are compared with a theoretical calculation. In the thinnest QW investigated (80 angstroms) the in-plane mass is found to increase by about 50% compared to the bulk GaInAs value.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.