Lithium-Doped Two-Dimensional Perovskite Scintillator for Wide-Range Radiation Detection

Two-dimensional lead halide perovskites have demonstrated their potential as high-performance scintillators for X- and gamma-ray detection, while also being low-cost. Here we adopt lithium chemical doping in two-dimensional phenethylammonium lead bromide (PEA)2PbBr4 perovskite crystals to improve the properties and add functionalities with other radiation detections. Li doping is confirmed by X-ray photoemission spectroscopy and the scintillation mechanisms are explored via temperature dependent X-ray and thermoluminescence measurements. Our 1:1 Li-doped (PEA)2PbBr4 demonstrates a fast decay time of 11 ns (80%), a clear photopeak with an energy resolution of 12.4%, and a scintillation yield of 11,000 photons per MeV under 662 keV gamma-ray radiation. Additionally, our Li-doped crystal shows a clear alpha particle/gamma-ray discrimination and promising thermal neutron detection through 6Li enrichment. X-ray imaging pictures with (PEA)2PbBr4 are also presented. All results demonstrate the potential of Li-doped (PEA)2PbBr4 as a versatile scintillator covering a wide radiation energy range for various applications

Testbeds for Transition Metal Dichalcogenide Photonics: Efficacy of Light Emission Enhancement in Monomer vs. Dimer Nanoscale Antennae

Monolayer transition metal dichalcogenides are uniquely-qualified materials for photonics because they combine well defined tunable direct band gaps and selfpassivated surfaces without dangling bonds. However, the atomic thickness of these 2D materials results in low photo absorption limiting the achievable photo luminescence intensity. Such emission can, in principle, be enhanced via nanoscale antennae resulting in; a. an increased absorption cross-section enhancing pump efficiency, b. an acceleration of the internal emission rate via the Purcell factor mainly by reducing the antennas optical mode volume beyond the diffraction limit, and c. improved impedance matching of the emitter dipole to the freespace wavelength. Plasmonic dimer antennae show orders of magnitude hot-spot field enhancements when an emitter is positioned exactly at the midgap. However, a 2D material cannot be grown, or easily transferred, to reside in mid-gap of the metallic dimer cavity. In addition, a spacer layer between the cavity and the emissive material is required to avoid non-radiative recombination channels. Using both computational and experimental methods, in this work we show that the emission enhancement from a 2D emitter- monomer antenna cavity system rivals that of dimers at much reduced lithographic effort. We rationalize this finding by showing that the emission enhancement in dimer antennae does not specifically originate from the gap of the dimer cavity, but is an average effect originating from the effective cavity crosssection taken below each optical cavity where the emitting 2D film is located. In particular, we test an array of different dimer and monomer antenna geometries and observe a representative 3x higher emission for both monomer and dimer cavities as compared to intrinsic emission of Chemical Vapor Deposition synthesized WS2 flakes.Comment: 31 pages, 5 figure

Visible spectrum quantum light sources based on InxGa1–xN/GaN Quantum Dots

We present a method for designing quantum light sources, emitting in the visible band, using wurtzite InxGa1−xN quantum dots (QDs) in a GaN matrix. This system is significantly more versatile than previously proposed arsenide- and phosphide-based QDs, having a tuning range exceeding 1 eV. The quantum mechanical configuration interaction method, capturing the fermionic nature of electrons and associated quantum effects explicitly, is used to find shapes and compositions of dots to maximize the excitonic dipole matrix element and optimize the biexciton binding energy. These results provide QD morphologies tailored for either bright single-photon emission or entangledphoton- pair emission at any given wavelength in the visible spectrum

Observation of fluctuations of the local density of states in disordered photonic media

Local density of states (LDOS) uniquely describes the available optical eigenmodes in which photons can exist at a specific spatial location. The LDOS controls the spontaneous emission, which is a fundamental phenomenon associated with the creation of light from the source. In disordered photonic media, the average LDOS is independent of the photonic properties, and only scales with the effective refractive index. Instead, strong sample- to-sample fluctuations of the LDOS are the characteristics of a disordered medium. Qualitative calculations of the fluctuations of the LDOS were previously made in the contexts of the nonlinear sigma model and the intensity correlations in speckle patterns. To date, however, there have not been any experiments to confirm this theory. This paper investigates spontaneous emission of emitters in the disordered photonic media. Time-resolved measurements on single polystyrene spheres incorporated with dye molecules, which are embedded inside a disordered layer of ZnO nanoparticles, are done. Fluorescence images of single fluorescent spheres embedded in a 4.8 mum-thick layer of ZnO pgiment at a depth of 2.5 mum are obtained