Polarization-dependent Photoluminescence 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.

Investigation of exciton states of ReS2 by temperature- and polarization-dependent photoluminescence and oxygen plasma treatment

Rhenium disulfide (ReS2) is a 1T′ phase, direct band-gap layered semiconductor with in-plane anisotropy of optical and electrical properties. It has been researched extensively for polarization-sensitive optoelectronic applications in the energy range of visible light. However, the comprehensive excitonic states of ReS2, including the emission induced by incidental defects such as sulfur vacancies, have not been investigated fully. We performed temperature- and polarization-dependent photoluminescence (PL) measurements to study the exciton states of ReS2 with thicknesses varying from monolayer to multilayer. Notably, we firstly identified the PL peak at ∼1.4 eV (X0). It showed a gradual enhancement by the oxygen plasma treatment. The X0 peak showed an isotropic polarization of the PL. This was distinguished from the linearly polarized emission of the other PL peaks of ReS2. Density functunal theory (DFT) calculations predicted the narrowing of the bandgap by the formation of ReO bonds at the sulfur vacancy sites. This is consistent with the observed energy of X0. Our comprehensive investigation of the four excitonic transitions of ReS2 including X0 impurity state, expands the utility of anisotropic ReS2 as a practical optoelectronic device.

Growth evolution and polarization-dependent photoluminescence of lateral InSb/CdTe nanowires

The evolution of lateral InSb nanowires (NW) grown on CdTe (001) substrate by increasing of the InSb thickness is reported. At 10-nm growth of InSb, NW with narrow lateral width of ∼ 70 nm and high NW density (∼18 μm−1) are obtained. The evolutional description of InSb NW growth based on the atomic force microscopic characterization is presented. The intrinsic strain at the interface and top InSb layer is revealed by x-ray diffraction analysis. The strong polarization-dependent photoluminescence (PL) of NW is observed. The polarization degree of NW is ∼ 80% and 56% when the excited laser and the emission PL are polarized, respectively. The latter can be attributed to the shape anisotropy.

Optical polarization properties of TPP2MnBr4 perovskite crystal adjusted by the self-trapping state.

Low-dimensional networked organic-inorganic hybrid metal halide crystal has become an emerging hotspot material due to its opportunities and advantages in the development of white-light-emitting diodes. Therefore, its photoluminescence (PL) mechanism is important. Herein, we study the PL behavior of columniform TPP2MnBr4 crystals using multi-spectroscopy. The temperature-dependent PL data show that the PL of the TPP2MnBr4 crystal originates from the recombination of a self-trapping exciton. A polarization-dependent PL test suggests that the self-trapping exciton is anisotropic, which indicates that the distribution of self-trapping states is sensitive to the orientation of the crystal axis. Space-resolved PL spectroscopy shows that the anisotropy of PL gradually weakens along the orientation of the columniform crystal, which has a longer relaxation distance than traditional light-wave-guiding behavior. Thus, anisotropy of PL can exist before it disappears in the crystal. Our results elucidate the PL mechanism of low-dimensional networked organic-inorganic hybrid metal halide crystals and provide a foundation for advanced optical polarization devices based on them.

Optical Signal Modulation in Photonic Waveguiding Heteroarchitectures with Continuously Variable Visible-To-Near-Infrared Emission Color.

Photonic circuit systems based on optical waveguiding heteroarchitectures have attracted considerable interest owing to their potential to overcome the speed limitation in electronic circuits by modulating the optical signal at the micro- or nanoscale. However, controlling the parameters, including the wavelength and polarization of the light outcoupling, as well as the sequence among different building blocks, remains a key issue. Herein, supramolecular heteroarchitectures made by phosphorescent organometallic complexes of Pt, Pd, Cu, and Au are applied as photonic logic gates that show continuously variable emission colors from 475 to 810nm, low waveguide losses down to 0.0077dBµm-1 , and remarkable excitation-light polarization-dependent photoluminescence with anisotropy ratios up to 0.68. The sequences among Pt, Pd, Au, and Cu building blocks in the heteroarchitectures are controlled by living supramolecular polymerization or crystallization-driven self-assembly synthetic approaches. The results indicate the prospects for using organometallic complexes and supramolecular synthetic approaches to prepare photonic circuit systems with tunable emission color and controllable sequences among different blocks that achieve modulation of the optical signal in the visible-to-near-infrared spectral region.

Polarization-dependent photoluminescence properties of fab-compatible nanowire-based nanophotonic structures

Semiconductor nanowires show great potential for controlling light–matter interactions. Moreover, their polarization-dependent optical properties, primarily enabled by their dielectric mismatch, are a significant requisite for a plethora of emerging applications spanning from polarized photodetection to quantum photonics and quantum communication. Herein, we study the polarization dependence of photoluminescence (PL) properties from fab-compatible nanophotonic structures, comprising arrays of ultrathin (20 nm) silicon carbide nanowires (NWs) doped with oxygen and erbium ions. Polarization-resolved PL studies demonstrate a significant excitation polarization anisotropy (∼0.7) of the visible NW PL for light polarized parallel and perpendicular to the NWs' long axis. This anisotropic behavior agrees with our simulations and with the classical dielectric contrast model and is consistent across the investigated periodicity range of the NW arrays. Furthermore, the effect of this anisotropy on the NW carrier dynamics is explored through power-dependence and transient PL measurements. We have observed a faster carrier lifetime for light polarized parallel to the NWs than the perpendicular polarization. Finally, we demonstrate a translation of this polarization dependence to the technologically significant erbium-induced 1540 nm emission from the erbium centers in the NW arrays. The ability to engineer emission polarization and placement of these centers in the NW array offers a promising platform for emission enhancement of telecom emitters through effective coupling to optical nanocavities for applications in chip-scale photonics and quantum photonics.

Polarization-controlled anisotropy in hybrid plasmonic nanoparticles

Abstract Anisotropy has played a critical role in many material systems, but its controllable creation and modulation have been a long-lasting challenge for the scientific communities. Polarization-addressed anisotropy appears more attractive among all approaches due to its excellent controllability, simplicity, and accuracy, but only a limited number of material systems are applicable for such a concept, which are largely focused on oriented growth. Here, we establish a polarization-dependent anisotropic etching system made of Au@oligomer core–shell nanoparticles (NPs). As the oligomer coatings can be photochemically degraded via two-photon photolithography, the plasmonic near-field enhancement supported by the Au NP cores renders much faster degradation of the oligomer shells along the polarization, resulting in anisotropic Au@oligomer hybrid NPs. Such shape anisotropy leads to polarization-dependent photoluminescence with embedded dyes of methylene blue, which can be used as single-particle-based polarization detector. The oligomer lobes capped at the sides of the Au NP can also function as a protection agent for anisotropic photochemical growth of Au NPs, which evolve into Au nanorods and mushrooms with controlled irradiation time. Such polarization-directed etching of oligomer shells has unique advantages of high local-selectivity, controllability, and versatility for on-chip nanofabrication, which opens many new opportunities for integrated nanophotonic devices.

Growth-related photoluminescence properties of InSb/GaAs self-assembled quantum dots grown on (001) Ge substrates

Various photoluminescence (PL) spectroscopies are applied to reveal the growth-related properties of self-assembled InSb/GaAs quantum dots (QDs) grown on (001) Ge substrate. Obtained QDs have rectangular-based shape and mainly locate near GaAs antiphase domain boundaries (APBs), which are formed during the growth of GaAs on (001) Ge substrate. The morphology and structural properties of InSb QDs can be varied by the change of controlled growth conditions. Optical phonons scatterings of the embedded InSb QDs are revealed by Raman spectroscopy. The low-temperature PL emission energy of InSb/GaAs QDs is in the range of 1.18–1.29 eV. The power-dependent PL spectroscopy confirms the type-II band alignment in this system. The thermal activation energies (22.7 meV and 146.5 meV) are extracted from the temperature-dependent PL spectroscopy (10–140 K). The polarization-dependent PL spectroscopy is performed and exhibits the polarization degree of ~ 18%, which is attributed to the shape anisotropy of buried InSb QDs.

Light Capture and Energy Conversion in Plasmonic-Polymeric Hybrid Nanoelectrodes

Plasmonic nanomaterials have absorption cross-sections exceeding other classes of materials but dephase quickly into their dielectric environment. In this work, plasmonic-polymeric nanoantenna-reactor systems are hybridized to increase the electron-hole pair lifetime through interfacial redistribution. The electron-hole pair can then be extracted to drive catalysis as the selected polymeric acceptor, a metallophthalocyanine, has been shown to catalysis O2 and CO2 reduction efficiently. Single particle spectroelectrochemistry was used to characterize the energy transfer efficiencies of the hybrid structures by recording the surface plasmon resonance energy linewidth change during in situ polymerization. The electrochemical polymerization is selective and photoenhanced on the surface of the gold nanorods. We complement resonance energy transfer efficiencies calculated from single particle changes in linewidth with calculations from excitation polarization-dependent photoluminescence measurements. Non-radiative energy transfer efficiencies up to 50% are achieved for plasmonic-polymeric nano-antenna reactors. The understanding of interfacial transfer pathways between plasmonic-polymeric materials will lead to control and tunability of scalable hybrid nanoelectrodes.

Thermally Assisted Rashba Splitting and Circular Photogalvanic Effect in Aqueously Synthesized 2D Dion-Jacobson Perovskite Crystals.

Recently, a two-dimensional Dion-Jacobson (DJ) perovskite (AMP)PbI4 (AMP = 4-(aminomethyl)piperidinium) is emerging with remarkable Rashba effect and ferroelectricity. However, the origin of the giant Rashba splitting remains elusive and the current synthetic strategy via slow cooling is time- and power-consuming, hindering its future applications. Here, we report on an economical aqueous method to obtain (AMP)PbI4 crystals and clarify the origin of the giant Rashba effect by temperature- and polarization-dependent photoluminescence (PL) spectroscopy. The strong temperature-dependent PL helicity indicates the thermally assisted structural distortion as the main origin of the Rashba effect, suggesting that valley polarization still preserves at high temperatures. The Rashba effect was further confirmed by the circular photogalvanic effect near the indirect bandgap. Our study not only optimizes the synthetic strategies of this DJ perovskite but also sheds light on its potential applications in room/high-temperature spintronics and valleytronics.

All-epitaxial long-range surface plasmon polariton structures with integrated active materials

We demonstrate all-epitaxial structures capable of supporting short- and long-range surface plasmon polariton (SRSPP and LRSPP) modes in the long-wave infrared region of the electromagnetic spectrum. The SRSPP and LRSPP modes are bound to the interfaces of a buried heavily doped (n++) semiconductor layer and surrounding quantum-engineered type-II superlattice (T2SL) materials. The surrounding T2SLs are designed to allow optical transitions across the frequency dispersion of the SPP modes. We map the SPP dispersion in our structure using grating-coupled angle- and polarization-dependent reflection and photoluminescence spectroscopy. The epitaxial structures are analytically described using a simplified three-layer system (T2SL/n++/T2SL) and modeled using rigorous coupled wave analysis with excellent agreement to our experimental results. The presented structures offer the potential to serve as long-range interconnects or waveguides in all-epitaxial plasmonic/optoelectronic systems operating in the long-wave infrared.

Highly Asymmetric Optical Properties of β-Ga2O3 as Probed by Linear and Nonlinear Optical Excitation Spectroscopy

Highly asymmetric optical properties of b-Ga2O3 are investigated by polarization-dependent photoluminescence (PL) excitation spectroscopy for assessing its potential use for a novel ultraviolet emitter and nonlinear optical material. Based on power-dependent excitation and two-photon depth scan, it is demonstrated that the underlying mechanism for the PL occurring far below the bandgap is not caused by intrinsic polaron effects, but by excitonic recombination at extrinsic defect sites.

Static Rashba Effect by Surface Reconstruction and Photon Recycling in the Dynamic Indirect Gap of APbBr3 (A = Cs, CH3NH3) Single Crystals.

Recently, halide perovskites have gained significant attention from the perspective of efficient spintronics owing to the Rashba effect. This effect occurs as a consequence of strong spin-orbit coupling under a noncentrosymmetric environment, which can be dynamic and/or static. However, there exist intense debates on the origin of broken inversion symmetry since the halide perovskites typically crystallize into a centrosymmetric structure. In order to clarify the issue, we examine both dynamic and static effects in the all-inorganic CsPbBr3 and organic-inorganic CH3NH3PbBr3 (MAPbBr3) perovskite single crystals by employing temperature- and polarization-dependent photoluminescence excitation spectroscopy. The perovskite single crystals manifest the dynamic effect by photon recycling in the indirect Rashba gap, causing dual peaks in the photoluminescence. However, the effect vanishes in CsPbBr3 at low temperatures (<50 K) accompanied by a striking color change of the crystal, arising presumably from lower degrees of freedom for inversion symmetry breaking associated with the thermal motion of the spherical Cs cation compared with the polar MA cation in MAPbBr3. We also show that the static Rashba effect occurs only in MAPbBr3 below 90 K, presumably due to surface reconstruction via MA-cation ordering, which likely extends across a few layers from the crystal surface to the interior. We further demonstrate that this static Rashba effect can be completely suppressed upon surface treatment with polymethyl methacrylate (PMMA) coating. We believe that our results provide a rationale for the Rashba effects in halide perovskites.

Polarization dependent photoluminescence and optical anisotropy in CuPtB-ordered dilute GaAs1–xBix alloys

The GaAs1–xBix semiconductor alloy allows one to achieve large bandgap reduction and enhanced spin–orbit splitting energy at dilute Bi quantities. The bismide is currently being developed for near- to mid-infrared lasers, multi-junction solar cells, and photodetectors. In this structure–property relationship study of GaAsBi alloys, we report polarization dependent photoluminescence that reaches a polarization ratio up to 2.4 at room temperature. Polarization dependence is also presented using transmittance spectra, birefringence, and linear dichroism. The optical anisotropy observations agree with the predictions of point symmetry reduction in the CuPtB-type ordered GaAsBi phase. The structural ordering is investigated experimentally from the atomic scale in molecular-beam epitaxy (MBE) grown samples on exact and miscut (001) GaAs substrates, as well as on (001) Ge. The latter sample is composed of anti-phase domains in which the ordering axes are rotated by 90° angles. Since the conditions stabilizing the CuPtB ordered phase fall within the typical MBE growth regime of dilute bismides, the optical anisotropy in GaAsBi alloys is expected to be ubiquitous. These findings are important for the future development of GaAsBi-based optoelectronics and also provide new means to analyze structurally complex bismide alloys.

Optical anisotropy of interface-bound exciton emission in a-plane ZnO/Zn1-xMgxO MQWs with Zn1-yMgyO buffer layer

The anisotropic exciton emission in a-plane nonpolar ZnO/ZnMgO MQWs offers opportunity for anisotropic photonic devices. By introducing Zn1-yMgyO buffer layer between r-plane sapphire substrate and MQWs, we investigated the structural and optical properties of ten-period a-plane ZnO/Zn1−xMgxO (ZnO/ZnMgO) multiple quantum wells (MQWs) with different widths of Zn1−xMgxO barrier layers grown by pulsed-laser deposition on Zn1-yMgyO buffered r-plane sapphire. Polarization-dependent photoluminescence spectra reveal that two additional linear polarizations of interface-bound exciton emission with E⊥c orienting at ~± 50° with respect to the regular a-plane MQWs are attributed to the generation of (0 0 0 2)-oriented nano-domains (NDs). As evidenced by XRD and TEM, we found four sets of (0 0 0 2)-oriented MQWs NDs are embedded in regular a-plane ZnO/ZnMgO MQWs with 90° in-plane rotation from one another which are inclined by 27.6° towards the [1 1 2¯ 0]-direction of the ZnO/ZnMgO MQWs. The existence of (0 0 0 2)-oriented NDs is further confirmed by the phase-contrast atomic force microscopy that modulates the optical anisotropy of interface-bound exciton emission in a-plane nonpolar ZnO/ZnMgO MQWs.

Multipoint Nanolaser Array in an Individual Core–Shell CdS Branched Nanostructure

AbstractNanoscale laser arrays are attractive for their potential applications in highly integrated nanodevices, which are always obtained by nanowire arrays with complicated fabrication techniques. Here, a quite different nanolaser array is successfully realized based on a highly ordered core–shell CdS branched nanostructure with implanted Sn nanoparticles in junctions that split the individual multichannel nanostructures to various microcavities with effective light confinement and oscillation, thus to achieve a multipoint nanolaser array. Under the excitation of an ultraviolet laser, the strong band‐edge emission can be well reflected between Sn nanoparticles at junctions and effectively scattered into branch segments due to Sn nanoparticles existence in junctions, furthermore oscillating in various microcavities along trunks or branches to form multipoint lasing from Fabry‐Pérot (F‐P) mode with a quality factor up to 990 and the low threshold at around 3.78 MW cm−2. The corresponding fluorescent microscope images further demonstrate the formation of multipoint F‐P lasing at various segments. The theoretical simulation indicates that implanted Sn nanoparticles work as hot point to enhance the confinement of light around the Sn centers. The existence of surface plasmon from the Sn metal particles is further confirmed by the polarization dependent photoluminescence measurement. The results provide a new way to realize nanolaser arrays.

Study of Oxidation and Polarization-Dependent Optical Properties of Environmentally Stable Layered GaTe Using a Novel Passivation Approach.

Emerging two-dimensional gallium chalcogenides, such as gallium telluride (GaTe), are considered promising layered semiconductors that can serve as vital building blocks towards the implementation of nanodevices in the fields of nanoelectronics, optoelectronics, and quantum photonics. However, oxidation-induced electronic, structural, and optical changes observed in ambient-exposed gallium chalcogenides need to be further investigated and addressed. Herein, we report on the thickness-dependent effect of air exposure on the Raman and photoluminescence (PL) properties of GaTe flakes, with thicknesses spanning in the range of a few layers to 100 nm. We have developed a novel chemical passivation that results in complete encapsulation of the as-exfoliated GaTe flakes in ultrathin hydrogen–silsesquioxane (HSQ) film. A combination of correlation and comparison of Raman and PL studies reveal that the HSQ-capped GaTe flakes are effectively protected from oxidation in air ambient over the studied-period of one year, and thus, preserving their structural and optical characteristics. This contrasts with the behavior of uncapped GaTe, where we observe a significant reduction of the GaTe-related PL (~100×) and Raman (~4×) peak intensities for the few-layered flakes over a period of few days. The time-evolution of the Raman spectra in uncapped GaTe is accompanied by the appearance of two new prominent broad peaks at ~130 cm−1 and ~146 cm−1, which are attributed to the formation of polycrystalline tellurium, due to oxidation of ambient-exposed GaTe. Furthermore, and by leveraging this novel passivation, we were able to explore the optical anisotropy of HSQ-capped GaTe flakes. This is caused by the one-dimensional-like nature of the GaTe layer, as the layer comprises Ga–Ga chains extending along the b-axis direction. In concurrence with high-resolution transmission electron microscopy analysis, polarization-dependent PL spectroscopy was used to identify the b-axis crystal direction in HSQ-capped GaTe flakes with various thicknesses over a range of wavelengths (458 nm–633 nm). Thus, our novel surface-passivation offers a new approach to explore and reveal the physical properties of the layered GaTe, with the potential of fabricating reliable polarization-dependent nanophotonics with structural and optical stability.

Direct observation of cross-polarized excitons in aligned single-chirality single-wall carbon nanotubes

Optical properties of single-wall carbon nanotubes (SWCNTs) for light polarized parallel to the nanotube axis have been extensively studied, whereas their response to light polarized perpendicular to the nanotube axis has not been well explored. Here, by using a macroscopic film of highly aligned single-chirality (6,5) SWCNTs, we performed a systematic polarization-dependent optical absorption spectroscopy study. In addition to the commonly observed angular-momentum-conserving interband absorption of parallel-polarized light, which generates $E_{11}$ and $E_{22}$ excitons, we observed a small but unambiguous absorption peak whose intensity is maximum for perpendicular-polarized light. We attribute this feature to the lowest-energy cross-polarized interband absorption processes that change the angular momentum along the nanotube axis by $\pm 1$, generating $E_{12}$ and $E_{21}$ excitons. The energy difference between the $E_{12}$ and $E_{21}$ exciton peaks, expected from asymmetry between the conduction and valence bands, was smaller than the observed linewidth. Unlike previous observations of cross-polarized excitons in polarization-dependent photoluminescence and circular dichroism spectroscopy experiments, our direct observation using absorption spectroscopy allowed us to quantitatively analyze this resonance. Specifically, we determined the energy and oscillator strength of this resonance to be 1.54 and 0.05, respectively, compared with the values for the $E_{11}$ exciton peak. These values, in combination with comparison with theoretical calculations, in turn led to an assessment of the environmental effect on the strength of Coulomb interactions in this aligned single-chirality SWCNT film.

Incident wavelength and polarization dependence of spectral shifts in \u03b2-Ga2O3 UV photoluminescence

We report polarization dependent photoluminescence studies on unintentionally-, Mg-, and Ca-doped β-Ga2O3 bulk crystals grown by the Czochralski method. In particular, we observe a wavelength shift of the highest-energy UV emission which is dependent on the pump photon energy and polarization. For 240 nm (5.17 eV) excitation almost no shift of the UV emission is observed between E||b and E||c, while a shift of the UV emission centroid is clearly observed for 266 nm (4.66 eV), a photon energy lying between the band absorption onsets for the two polarizations. These results are consistent with UV emission originating from transitions between conduction band electrons and two differentially-populated self-trapped hole (STH) states. Calcuations based on hybrid and self-interaction-corrected density functional theories further validate that the polarization dependence is consistent with the relative stability of two STHs. This observation implies that the STHs form primarily at the oxygen atoms involved in the original photon absorption event, thus providing the connection between incident polarization and emission wavelength. The data imposes a lower bound on the energy separation between the self-trapped hole states of ~70–160 meV, which is supported by the calculations.

The optical and structure properties of high-quality InGaN/GaN epilayers grown on miscut sapphire substrate

We report on structural and optical properties of InGaN/GaN thin films, with a 0.46o misalignment between the surface and the (0001) plane, which were grown by metal-organic chemical vapor deposition (MOCVD) on 0.34o miscut sapphire substrates. X-ray diffraction and X-ray reflectivity were used to precisely measure the degree of miscut. Reciprocal space mapping was employed to determine the lattice parameters and strain state of the InGaN layers. Rutherford backscattering spectrometry with channeling was employed to measure their composition and crystalline quality with depth resolution. No strain anisotropy was observed. Polarization-dependent photoluminescence spectroscopy was carried out to examine the effect of the miscut on the bandedge emission of the epilayer.