Spontaneous emission

About: Spontaneous emission is a research topic. Over the lifetime, 12855 publications have been published within this topic receiving 323684 citations.

Control of Interface Defects for Efficient and Stable Quasi-2D Perovskite Light-Emitting Diodes Using Nickel Oxide Hole Injection Layer.

Abstract: Metal halide perovskites (MHPs) have emerged as promising materials for light-emitting diodes owing to their narrow emission spectrum and wide range of color tunability. However, the low exciton binding energy in MHPs leads to a competition between the trap-mediated nonradiative recombination and the bimolecular radiative recombination. Here, efficient and stable green emissive perovskite light-emitting diodes (PeLEDs) with an external quantum efficiency of 14.6% are demonstrated through compositional, dimensional, and interfacial modulations of MHPs. The interfacial energetics and optoelectronic properties of the perovskite layer grown on a nickel oxide (NiO x ) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate hole injection interfaces are investigated. The better interface formed between the NiO x /perovskite layers in terms of lower density of traps/defects, as well as more balanced charge carriers in the perovskite layer leading to high recombination yield of carriers are the main reasons for significantly improved device efficiency, photostability of perovskite, and operational stability of PeLEDs.

Localized quantum well excitons in InGaN single-quantum-well amber light-emitting diodes

Abstract: Optical properties of the InGaN single-quantum-well amber light-emitting-diodes were investigated to verify the importance of localized quantum well (QW) excitons in their spontaneous emission mechanisms. The internal piezoelectric field (FPZ) across the QW of the order of 1.4 MV/cm was confirmed to point from the surface to the substrate. Transmittance and photovoltaic spectra exhibited a broad band tail state, and the emission lifetime increased with decreasing detection photon energy. The electroluminescence spectra did not show remarkable energy shift between 10 and 300 K. The spectra exhibited an exponential tail and the higher energy portion increased more rapidly than that of the lower energy one, reflecting a thermal distribution of the localized carriers within the tail states. Since the well thickness is only 2.5 nm and is atomically flat, the device is considered to exhibit reasonably efficient emission with the external quantum efficiency of 5% at 20 mA in spite of the presence of FPZ and larg...

Stimulated Emission at Blue-Green (480 nm) and Green (514 nm) Wavelengths from Nonpolar (m-plane) and Semipolar (1122) InGaN Multiple Quantum Well Laser Diode Structures

Abstract: Stimulated emission (SE) in the blue-green (480 nm) and green (514 nm) regime has been observed, at room temperature (RT) under optical pumping, from nonpolar m-plane (1010) and semipolar (1122) InGaN multi-quantum well (MQW) laser diode (LD) structures, respectively, grown on bulk GaN substrates. The emission intensity exhibited a clear threshold behavior with respect to the pump power. Optical anisotropy was also observed between the two perpendicular in-plane directions [1123] and [1010] for semipolar LD structures, with significantly lower pump thresholds for emission along [1123]. The SE wavelength, measured just above threshold, was blue-shifted with respect to the spontaneous emission wavelength measured just below threshold. These initial results indicate that semipolar (1122) GaN is a promising orientation for the realization of blue-green and green LDs.

Quantum theory of phonon-assisted exciton formation and luminescence in semiconductor quantum wells

Abstract: The phonon scattering assisted luminescence of semiconductor quantum well excitons after short pulse excitation is investigated. The presented analysis is based on the low-density limit of a set of equations for quantum correlation functions for electrons, phonons, and photons. The dynamics of the correlation functions describes the optical excitation and the decay of the coherent exciton polarization as well as the generation of an incoherent exciton occupation and its luminescence decay. Numerical solutions of the equations of motion demonstrate strong competition effects of the exciton-phonon and the exciton-photon interaction on a picosecond time scale and lead to a nonmonotonous temperature dependence of the time-resolved spontaneous emission. The angle resolved emission resembles the generation and decay dynamics of the exciton density for different in-plane momenta.

Spontaneous emission rate of an excited atom placed near a nanofiber (17 pages)

Abstract: The spontaneous decay rate of an excited atom placed near a dielectric cylinder is investigated. Special attention is paid to the case when the cylinder radius is small in comparison with radiation wavelength (nanofiber or photonic wire). In this case, the analytical expressions of the transition rates for different orientations of a dipole are derived. It is shown that the main contribution to decay rates is due to the quasistatic interaction of the atom dipole momentum with the nanofiber, and the contributions of guided modes are exponentially small. On the contrary, in the case when the radius of the fiber is only slightly less than the radiation wavelength, the influence of guided modes can be substantial. The results obtained are compared with the case of a dielectric nanospheroid and an ideally conducting wire.