Polarization-dependent Emission Research Articles

Polarization-dependent photoluminescence of Ce-implanted MgO and MgAl2O4

Since the qubit’s performance of solid-state spin centers depends highly on the host material, spin centers using new host materials may offer new qubit applications. We investigate the optical properties of Ce-implanted MgO and MgAl2O4 as potential materials holding the optically accessible qubit. We find that the photoluminescence of Ce-implanted MgAl2O4 is more than 10 times brighter than that of Ce-implanted MgO and observe polarization-dependent emission of Ce center in MgAl2O4 with 2% at 4 K under 500 mT, suggesting that the properties required for initializing and reading the state of the spin qubit have been achieved.

Suppressed Blinking and Polarization-Dependent Emission Enhancement of Single ZnCdSe/ZnS Dot Coupled with Au Nanorods.

Fluorescent quantum dots (QDs) have attracted extensive attention because of their promising applications in many fields such as quantum optics, optoelectronics, solid-state lighting, and bioimaging. However, photo-blinking, low emission efficiency, and instability are the drawbacks of fluorescent QD-based devices, affecting their optical properties and practical applications. Here, we report suppressed blinking, enhanced radiative rate, and polarization-dependent emission properties of single ZnCdSe/ZnS QDs assembled on the surface of Au nanorods (NRs). We found that the local surface plasmon (LSP) of Au NRs significantly regulates the excitation and emission properties of the composite ZnCdSe/ZnS QD-Au NRs (QD-Au NRs). The average number of photons emitted per unit time from single QD-Au NRs has been significantly enhanced compared with that of single ZnCdSe/ZnS QDs on the coverslip, accompanied by a drastically shortened lifetime and suppressed blinking. According to the experimental and simulation analysis, the photogenerated LSP field of Au NRs remarkably increases the excitation transition and the radiative rates of QD-Au NRs. Although the emission efficiency is slightly increased, the synergetic enhancement of excitation and radiative rates sufficiently competes with the nonradiative process to compensate for the low emission efficiency of QDs and ultimately suppress the photo-blinking of QD-Au NRs. Moreover, the polarization-dependent emission enhancement has also been observed and theoretically analyzed, demonstrating good consistency and confirming the contribution of excitation enhancement. Our findings present a practical strategy to improve the optical properties and stability of single QD-Au NR composite and provide essential information for a deep understanding of the interaction between emitters and the LSP field of metal nanoparticles.

Self-assembled ultrafine CsPbBr3 perovskite nanowires for polarized light detection

One-dimensional (1D) metal halide perovskite nanowire (NW) arrays with high absorption efficiency, emission yield and dielectric constants, as well as anisotropic optoelectronic properties have found applications in energy harvesting, flexible electronics, and biomedical imaging devices. Here, a modified two-step solvothermal method is developed for the synthesis of self-assembled cubic CsPbBr3 NW arrays. This method provides facile access to continuous and uniform ultrafine perovskite NWs and well-aligned pure perovskite NW arrayed architectures. Under excitation at 365 nm, the CsPbBr3 NWs give a strong blue emission observable to the naked eyes. The CsPbBr3 NWs also exhibit strong two-photon excited luminescence under the irradiation with an 800 nm pulse laser. By rotating the polarization angle of the 800 nm laser, strong polarization dependence with a polarization degree up to ∼0.49 is demonstrated in the self-assembled CsPbBr3 NW array, although the CsPbBr3 NWs have an isotropic cubic structure. Based on density functional theory (DFT) calculations, this polarization-dependent emission is correlated with the anisotropic charge density distribution of the perovskite NWs. These findings suggest that the ultrafine CsPbBr3 NWs with a well-defined self-assembled architecture could be applied as next-generation polarization-sensitive photoelectronic detection materials.

Spatially and temporally polarization shaped laser pulses for two-photon excited fluorescence

We present simultaneous spatial and temporal polarization pulse shaping for two-photon excited fluorescence of dyes. A temporal pulse shaper and a subsequent spatial pulse shaper are used to generate laterally and axially tailored two-photon excited fluorescence profiles. The induced fluorescence is recorded for different polarization directions by utilizing the anisotropy of the dyes embedded in glycerol. We achieve an increased fluorescence contrast between different dyes by employing specific polarization shaped laser pulses and by taking polarization dependent emission into account. This versatile pulse shaping method is prospective for novel biophotonic imaging.

Anisotropy of Excitons in Two-Dimensional Perovskite Crystals.

Two-dimensional (2D) perovskites show great potential for optoelectronic applications due to their bandgap tunability, extremely large excition binding energy, and large crystal anisotropy compared with their three-dimensional counterparts. To fully explore exciton-based applications and improve their performance, it is essential to understand the exciton behavior in 2D perovskites. Here, we investigate exciton anisotropy within the crystallographic plane and cross plane of (C4H9NH3)2PbI4 2D perovskite crystals by polarization-resolved photoluminescence, reflection, and photoconductivity studies. We observe a polarization-dependent emission evolution and an enhanced self-trapped exciton emission with an oblique incident excitation from the cross plane. Furthermore, the anisotropy of excitons in (C4H9NH3)2PbI4 2D perovskite crystals is identified by polarization-resolved photoluminescence and photoconductivity measurement, and a completely opposite polarization-dependent behavior was observed for free excitons and self-trapped excitons. We attribute this different anisotropy to the existence of out-of-plane excitons and different optical selection rule for free excitons and self-trapped excitons. Our findings will shed light on designing and improving the performance of exciton-based optoelectronic devices in 2D perovskites.

Broadened Bandwidth Amplified Spontaneous Emission from Blue GaN-Based Short-Cavity Superluminescent Light-Emitting Diodes

We report broad bandwidth blue superluminescent light-emitting diodes (SLEDs) based on a short-cavity active region. The dependencies of amplified spontaneous emission (ASE) output power and gain bandwidth on cavity length were investigated in devices whose gain medium consists of a ridge waveguide with embedded InGaN/GaN quantum wells sandwiched between one etched facet coated with a high reflectivity distributed Bragg mirror and one cleaved facet with an anti-reflection coating. 250 μm-long blue SLEDs exhibit a spectral bandwidth up to 7.5 nm at 1.72 mW output power at a wavelength of 427 nm. As cavity length decreases, the bandwidth gradually broadens up to 15 nm for the shortest, 40 μm-long, SLED devices. ASE is confirmed by current-dependent electroluminescence spectra and polarization-dependent emission intensity measurements. The optical features of those short-cavity devices could be helpful for designing broad bandwidth SLEDs aiming for various applications such as optical coherence tomography, next generation displays, on-chip biosensing and imaging.

Magnetically controllable random laser in ferromagnetic nematic liquid crystals.

This paper first reports random laser action in dye-doped ferromagnetic nematic liquid crystals, which act as a randomly distributed cavity. The random laser intensity of the ferromagnetic nematic liquid crystals can be controlled by a weak magnetic field (∼1 mT). Moreover, the magnetic switching of random laser is attributed to the direction and polarization dependent emission of light in the ferromagnetic nematic liquid crystals in an external magnetic field.

Lasing of Nd3+ in sapphire

AbstractWe present a rare‐earth‐doped sapphire laser. Single‐crystalline α‐Al2O3 films doped with trivalent neodymium have been grown by pulsed laser deposition on undoped sapphire substrates. The Nd3+ doping concentrations of the films have been varied between 0.3 at.% and 2 at.%. Epitaxial growth was proven by structural and optical characterization of the films. The samples exhibit strongly polarization dependent emission transitions from the 4F3/2 manifold with a fluorescence lifetime of 108 μs and peak emission cross sections of 1.1 × 10−18 cm2 around 1100 nm. Lasing at 1096.5 nm was achieved under Ti:sapphire‐pumping in a planar waveguide configuration with a maximum cw output power of 137 mW and a slope efficiency of 7.5% with respect to the incident pump power. image

Azimuthally polarized cathodoluminescence from InP nanowires

We determine the angle and polarization dependent emission from 1.75 µm and 2.50 µm long InP nanowires by using cathodoluminescence polarimetry. We excite the vertical wires using a 5 keV electron beam, and find that the 880 nm bandgap emission shows azimuthally polarized rings, with the number of rings depending on the wire height. The data agree well with a model in which spontaneous emission from the wire emitted into the far field interferes with emission reflected off the substrate. From the model, the depth range from which the emission is generated is found to be up to 400 nm below the top surface of the wires, well beyond the extent of the primary electron cloud. This enables a probe of the carrier diffusion length in the InP nanowires.

Plasmon-Mediated Whispering-Gallery-Mode Emission from Quantum-Dot-Coated Gold Nanosphere

Plasmons of gold nanostructures provide a powerful tool to enhance exciton–exciton coupling and energy transfer at spherical geometry, while quantum dots have confined excitons with strong optical oscillator strength and gain. Here, we report a plasmon-mediated whispering-gallery-mode emission from CdSe-ZnS quantum dot-coated gold nanosphere at room temperature. The whispering-gallery-mode emissions with different gold nanosphere sizes have been studied. Polarization-dependent emission is observed and explained. The decay dynamics of radiative emission is investigated by analyzing the photoluminescence decay spectrum. The underlying physical mechanism of the measured interference rings is further investigated by spatial distribution of photoluminescence intensity.

Probing orbital symmetry in solution: polarization-dependent resonant inelastic soft x-ray scattering on liquid micro-jet

Polarization-dependent resonant inelastic x-ray scattering is demonstrated here for liquid acetonitrile, acetone and dimethyl sulfoxide, using the liquid micro-jet technique. Selective excitation to an unoccupied orbital with a specific symmetry at the K-edge x-ray absorption of liquid samples determines the polarization-dependent emission of the occupied states. Considering the well-defined unoccupied molecular orbital configuration and utilizing the results of ab initio molecular orbital calculations, the polarization-dependent anisotropy in resonant inelastic soft x-ray scattering is discussed in a membrane-free configuration.

Molecular-scale simulation of electroluminescence in a multilayer white organic light-emitting diode

In multilayer white organic light-emitting diodes the electronic processes in the various layers--injection and motion of charges as well as generation, diffusion and radiative decay of excitons--should be concerted such that efficient, stable and colour-balanced electroluminescence can occur. Here we show that it is feasible to carry out Monte Carlo simulations including all of these molecular-scale processes for a hybrid multilayer organic light-emitting diode combining red and green phosphorescent layers with a blue fluorescent layer. The simulated current density and emission profile are shown to agree well with experiment. The experimental emission profile was obtained with nanometre resolution from the measured angle- and polarization-dependent emission spectra. The simulations elucidate the crucial role of exciton transfer from green to red and the efficiency loss due to excitons generated in the interlayer between the green and blue layers. The perpendicular and lateral confinement of the exciton generation to regions of molecular-scale dimensions revealed by this study demonstrate the necessity of molecular-scale instead of conventional continuum simulation.

Spatial resolution of methods for measuring the light-emission profile in organic light-emitting diodes

An analysis is presented of the resolution limits of two alternative methods for deducing the light-emission profile in organic light-emitting diodes (OLEDs) from the angular and polarization dependent emission spectra. The comparison includes the “fit-profile” (FP) method, within which the known physics of the recombination process is employed to describe the shape of the profile using a strongly reduced number of degrees of freedom, and the Tikhonov method, which provides a more general solution. First, the cases of a delta-function shaped emission profile and a broad single-peak emission profile are investigated. It is demonstrated that for these cases a ∼1 nm resolution of the peak position may be obtained, provided that the peak is positioned optimally in the OLED microcavity. Subsequently, an analysis is given for a double-peak emission profile and for a rectangular profile, as may be obtained in multilayer OLEDs, revealing a resolution of ∼10 nm for the cases studied. It is suggested that, in general, an optimal analysis should be based on a combined Tikhonov-FP approach.

Optimizing H1 cavities for the generation of entangled photon pairs

We report on the theoretical investigation of photonic crystal cavities etched on a suspended membrane for the generation of polarization entangled photon pairs using the biexciton cascade in a single quantum dot. The implementation of the spontaneous emission enhancement effect increases the entanglement visibility, while the concomitant preferential funneling of the emission in the cavity mode increases the collection of both entangled photons. We demonstrate and quantify that standard cavity designs present a polarization-dependent emission diagram, detrimental to entanglement. The optimization of H1 cavities allows us to obtain both high collection efficiencies and polarization-independent emission, while keeping the high Purcell factors necessary for high-quality entangled photon sources.

Anisotropy in the electronic structure ofV2GeCinvestigated by soft x-ray emission spectroscopy and first-principles theory

The anisotropy of the electronic structure of ternary nanolaminate V2GeC is investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured polarization-dependent emission spectra of V L2,3, C K, Ge M1 and Ge M2,3 in V2GeC are compared to those from monocarbide VC and pure Ge. The experimental emission spectra are interpreted with calculated spectra using ab initio density-functional theory including dipole transition matrix elements. Different types of covalent chemical bond regions are revealed; V 3d - C 2p bonding at -3.8 eV, Ge 4p - C 2p bonding at -6 eV and Ge 4p - C 2s interaction mediated via the V 3d orbitals at -11 eV below the Fermi level. We find that the anisotropic effects are high for the 4p valence states and the shallow 3d core levels of Ge, while relatively small anisotropy is detected for the V 3d states. The macroscopic properties of the V2GeC nanolaminate result from the chemical bonds with the anisotropic pattern as shown in this work.

EOS MLS forward model polarized radiative transfer for Zeeman-split oxygen lines

This work supplements the Earth Observing System (EOS) Microwave Limb Sounder (MLS) clear-sky unpolarized forward model with algorithms for modeling polarized emission from the Zeeman-split 118.75-GHz O/sub 2/ spectral line. The model accounts for polarization-dependent emission and for correlation between polarizations with complex, 2/spl times/2 intensity and absorption matrices. The oxygen line is split into three Zeeman components by the interaction of oxygen's electronic spin with an external magnetic field, and the splitting is of order /spl plusmn/0.5 MHz in a typical geomagnetic field. Zeeman splitting is only significant at pressures low enough that collisional broadening (/spl sim/1.6 MHz/hPa) is not very large by comparison. The polarized forward model becomes significant for MLS temperature retrievals at pressure below 1.0 hPa and is crucial at pressures below /spl sim/0.03 hPa. Interaction of the O/sub 2/ molecule with the radiation field depends upon the relative orientation of the radiation polarization mode and the geomagnetic field direction. The model provides both limb radiances and the derivatives of these radiances with respect to atmospheric temperature and composition, as required by MLS temperature retrievals. EOS MLS views the atmospheric limb at 118.75 GHz with a pair of linear-cross-polarized, 100-kHz-resolution, 10-MHz-wide spectrometers. The antennas of the associated receivers are scanned to view rays with tangent heights from the Earth's surface to 0.001 hPa. Comparisons of the modeled MLS radiances with measurements show generally good agreement in line positions and strengths, however residuals in the line centers at the highest tangent heights are larger than desired and still under investigation.

Dysprosium-doped YAl 3(BO 3) 4 (YAB) crystals: an investigation of radiative and non-radiative processes

The absorption, emission spectra and lifetime of the 4F 9/2 fluorescent level of Dy 3+ in YAl 3(BO 3) 4 crystal were investigated. Energy level structure was constructed from absorption and emission spectra recorded at 5 K. The measured oscillator strengths of the transitions between the J manifolds at 300 K were compared with those derived from the Judd–Ofelt theory. The radiative transition rates and radiative lifetimes were calculated. Although there are several transitions originating in the 4F 9/2 level a major part of emission intensity is contained in the 4F 9/2→ 6H 13/2 transition. Measurement of selfquenching of the 4F 9/2 luminescence provided a parameter characterizing an activator–activator interaction, which may be used to predict an optimal Dy 3+ concentration. The narrow and polarization dependent emission lines, relatively long lifetime of the 4F 9/2 metastable level ( τ=520 μs) and its high quantum efficiency are advantageous for low threshold laser action in both CW and pulsed operation. The emission cross-section of a potential laser line at 570 nm connected with 4F 9/2→ 6H 13/2 transition was estimated.

Cavity configuration for a Q-switched simultaneous dual-wavelength Nd:YAlO_3 laser with the characteristic of polarization-dependent emission cross section

By investigating the rate equations of Q-switched simultaneous dual-wavelength lasers and by using the polarization-dependent emission cross section of a Nd:YAlO3 laser crystal to balance the equivalent emission cross sections of the dual lasing wavelengths, we have developed a new resonator configuration by introducing a quarter-wave polarization rotator. The two wavelengths exhibit an equal net gain in the laser rod, and the optimal spatial and temporal overlap can be achieved easily for optimal sum-frequency mixing. This configuration has a cavity length that is shorter than in previously used configurations, so it is suitable for operation at high output power and with a high repetition rate with a short thermally determined focal length.