Enhanced Photoluminescence Emission Research Articles

Tailoring the luminescent and structural behaviors of pH-driven PPy/gC3N4/ZrO2 nanocomposite as an emissive layer material for OLED application

The polymeric nanocomposites were synthesized via an in-situ polymerization method, optimized through pH adjustment of zirconium oxide rather than concentration variation. X-ray powder diffraction analysis revealed phase transitions and average crystallite sizes ranging from approximately 6.52–9.16 nm, depending on the pH levels. Field Emission Scanning Electron Microscopy tool is used to analyze the granular nanosheets and nanoparticles like the microstructure of polypyrrole, graphitic carbon nitride and zirconium oxide at a high resolution. UV–visible spectroscopy determined an optical bandgap energy of about 2.44 eV, a refractive index of 2.17, and an optical conductivity of 3.15 × 1010 S/cm2. Forster resonance energy transfer between Zirconium dioxide and graphitic carbon nitride significantly enhanced photoluminescence emission. PL emission and color purity (45 %) of the optimized sample were examined using photoluminescence data. Electrical conductivity of ∼15.9 × 10−4 S/cm and dielectric constant of ∼14.77 were obtained from I to V and LCR meter measurements. These properties indicate that the pH-driven nanocomposite exhibits optimized electron-hole recombination rates, electrical conductivity, and suitable bandgap energy, making its potential impact as an emissive layer material for OLED applications.

Porous GaN Nanopyramids: Advancing Beyond Conventional Nanostructures for High‐Brightness InGaN/GaN Quantum Wells Emission

AbstractGaN nanostructures hold significant promise in advancing nanoscale light‐emitting devices. However, significant progress remains elusive, possibly due to the absence of innovative approaches. Beyond the smaller size of GaN nanostructures, the main interest lies in growing InGaN active layers on semi‐ and non‐polar orientations. Nevertheless, it is evident that while leveraging such a method holds initial promise, this approach may eventually reach its limits, prompting the need for fresh perspectives. In this manuscript, electrochemical etching is utilized to fabricate porous GaN nanopyramids. Given the absence of prior studies on electrochemical etching of GaN nanostructures, its etching behavior is investigated, revealing its selectivity concerning doping concentration and geometry. Furthermore, how the choice of electrolyte can differently impact the optical response of the etched template is explored. Subsequently, an InGaN/GaN quantum wells shell is grown as the active region. The significance of the approach is evidenced by a tenfold enhancement in photoluminescence emission. Porous nanopyramids demonstrate a higher internal quantum efficiency of 44.7% and faster radiative recombination time. Additionally, finite difference time domain simulation reveals a twofold increase in light extraction efficiency. This research will lead the way toward the development of a new class of nanostructures offering potential advancements in optoelectronic devices.

Photoluminescence emission enhancement in the LiSrVO4:Eu3+ vanadate phosphor by partial substitution of M+ ions (M+=Li+/Na+/K+); optical thermometry; and optical transition probabilities using Judd-Ofelt analysis

In solid state lighting (SSL), pcWLEDs gain more attention for various illumination applications. The Eu3+ activated LiSrVO4:xEu3+ (0–15 mol% in steps of 3) phosphors are prepared by the conventional solid state method and their phase formation is confirmed by PXRD. It suggest that the samples are in a monoclinic structure with P2/m space group. SEM results confirmed that the size of the prepared phosphor is in a micrometer range with an irregular spherical shape. The optical diffuse reflectance spectrum (DRS) consisted broad band absorption in the ultraviolet (UV) region (270–350 nm) and also, they are found to absorb strongly the NUV light (396 nm) and the blue light (466 nm). They exhibit the strongest emission at 617 nm for the samples under 326 nm excitation. The PL intensity of the phosphors are improved by co-doping. The optical transition probabilities of the LiSrVO4:9 mol% Eu3+ phosphor are also analyzed using the Judd-Ofelt theory. The optimized phosphor showed a good thermal stability and the lifetime values are in the millisecond range. The absolute and the relative sensitivities are obtained from the temperature dependent lifetime measurements. The LiSrVO4:9 mol%Eu3+ phosphor yielded CIE coordinates (x, y) of (0.5987, 0.4005), a low CCT of 1468K, and a color purity of 96.4 %. These results indicate the potential application of the LiSrVO4 based phosphors in WLEDs.

Enhanced photoluminescence emission intensity and stability of deep blue-emissive (Et3NH)PbBr3 perovskite nanocrystals by using metal-organic frameworks

The primary obstacle faced by researchers in the field of luminescent metal-halide perovskites is their inherent instability, prompting a shift in focus towards enhancing the stability of perovskite nanocrystals (PNCs). One of the promising approaches to address this challenge involves the utilization of metal-organic frameworks (MOFs) to fabricate PNCs@MOF composites. The present study reports a facile and low-cost colloidal strategy to prepare (Et3NH)PbBr3 PNCs followed by their encapsulation within UiO-67 to enhance their photoluminescence (PL) emission stability. The PNCs and modified UiO-67 were prepared separately via simple and efficient ligand-assisted reprecipitation (LARP) and hydrothermal methods, respectively. After modification of the UiO-67, the pore sizes experienced a substantial increase from 1.90 to 28.84 nm which significantly facilitated the localization of PNCs within the porous matrix. Under a full survey of experimental conditions, the resulting (Et3NH)PbBr3@UiO-67 composite exhibited a bright deep-blue emission at around 410 nm with an emission quantum yield of 52 %. The emission durability of the fabricated PNCs@MOF composites was assessed against temperature and long-time of storage, confirming the superior advantages of MOF even at elevated temperatures of up to 100 °C. The stable and luminous deep-blue emission displayed by the PNCs@MOF composites in this investigation, offers a promising advancement in materials development for optoelectronic applications.

Facile Access to High Solid Content Monodispersed Microspheres via Dual-Component Surfactants Regulation toward High-Performance Colloidal Photonic Crystals.

Monodispersed microspheres play a major role in optical science and engineering, providing ideal building blocks for structural color materials. However, the method toward high solid content (HSC) monodispersed microspheres has remained a key hurdle. Herein, a facile access to harvest monodispersed microspheres based on the emulsion polymerization mechanism is demonstrated, where anionic and nonionic surfactants are employed to achieve the electrostatic and steric dual-stabilization balance in a synergistic manner. Monodispersed poly(styrene-butyl acrylate-methacrylic acid) colloidal latex with 55wt% HSC is achieved, which shows an enhanced self-assembly efficiency of 280% compared with the low solid content (10wt%) latex. In addition, Ag-coated colloidal photonic crystal (Ag@CPC) coating with near-zero refractive index is achieved, presenting the characteristics of metamaterials. And an 11-fold photoluminescence emission enhancement of CdSe@ZnS quantum dots is realized by the Ag@CPC metamaterial coating. Taking advantage of high assembly efficiency, easily large-scale film-forming of the 55wt% HSC microspheres latex, robust Ag@CPC metamaterial coatings could be easily produced for passive cooling. The coating demonstrates excellent thermal insulation performance with theoretical cooling power of 30.4W m-2, providing practical significance for scalable CPC architecture coatings in passive cooling.

Insulating 6,6-Phenyl-C61-butyric Acid Methyl Ester on Transition-Metal Dichalcogenides: Impact of the Hybrid Materials on the Optical and Electrical Properties.

In this study we develop a strategy to insulate 6,6 -Phenyl C61 butyric acid methyl ester (PCBM) on the basal plane of transition metal dichalcogenides (TMDs). Concretely single layers of MoS2, MoSe2, MoTe2, WS2, WSe2 and WTe2 and ultrathin MoO2 and WO2 were grown via chemical vapor deposition (CVD). Then, the thiol group of a PCBM modified with cysteine reacts with the chalcogen vacancies on the basal plane of TMDs, yielding PCBM-MoS2, PCBM-MoSe2, PCBM-WS2, PCBM-WSe2, PCBM-WTe2, PCBM-MoO2 and PCBM-WO2. Afterwards, all the hybrid materials were characterized using several techniques, including XPS, Raman spectroscopy, TEM, AFM, and cyclic voltammetry. Furthermore, PCBM causes a unique optical and electrical impact in every TMDs. For MoS2 devices, the conductivity and photoluminescence (PL) emission achieve a remarkable enhancement of 1700 % and 200 % in PCBM-MoS2 hybrids. Similarly, PCBM-MoTe2 hybrids exhibit a 2-fold enhancement in PL emission at 1.1 eV. On the other hand, PCBM-MoSe2, PCBM-WSe2 and PCBM-WS2 hybrids exhibited a new interlayer exciton at 1.29-1.44, 1.7 and 1.37-154 eV along with an enhancement of the photo-response by 2400, 3200 and 600 %, respectively. Additionally, PCBM-WTe2 and PCBM-WO2 showed a modest photo-response, in sharp contrast with pristine WTe2 or WO2 which archive pure metallic character.

Pressure‐Induced Enhancement of Photoluminescence and Photocurrent in Organic Semiconductor Rubrene

AbstractAs a typical organic semiconductor material, rubrene plays a prominent role in the field of optoelectronic devices. Here, a notable photoluminescence (PL) and photocurrent enhancement of rubrene by 8‐ and 2.5‐fold is reported under compression, respectively. The shortening of the π−π stacking distance and the twisting of the lateral phenyl are crucial reasons for the decrease in the bandgap, resulting in the enhancement of PL emission and photocurrent. Pressure can effectively suppress the excitons transition from a free exciton state to a self‐trapped exciton state and improve the emission efficiency. The photocurrent is subject to dual regulation by bandgap and resistance. Interestingly, rubrene undergoes an electronic structure transition at about 4.8 GPa, which is responsible for the weakening of PL emission and photocurrent. This work provides a strategy for optimizing the performance of rubrene‐based optoelectronic devices and designing novel optoelectronic materials.

Influence of Au0 metallic particles on NIR laser emission of Yb3+ ions in Li2O−HfO2−SiO2 glass ceramic

This study consists of the synthesis, characterization, and analysis of photoluminescence (PL) spectra for Li2O−HfO2−SiO2−Yb2O3 glass ceramics sensitized with small amounts of Au2O3. Using the results of XRD and X-ray photoelectron spectroscopy (XPS) studies indicated a progressive reduction of Au3+ ions into Au0 metallic particles (MPs) with increase of Au2O3 content. Investigations into the infrared spectra highlighted a growing concentration of induced defects in the samples due to the increased proportion of Au0 MPs. Optical absorption (OA) spectra exhibited a distinct band attributed to the 2F7/2 → 2F5/2 transition of Yb3+ within wavelength range of 800–980 nm. Furthermore, a wide absorption band linked to the surface plasmon resonance (SPR) of Au0 MPs was identified in the visible region. PL spectra, recorded at λexc = 450 nm, revealed a band between 980 to 1025 nm, associated with the 2F5/2 → 2F7/2 transition of Yb3+ ions. Another emission band was observed due to the sp → d transition of Au0 MPs within the visible region. Observed enhanced PL emission from Yb3+ ions in the NIR range was ascribed to the energy transfer from Au0 MPs to Yb3+ ions. Ultimately, it was deduced that Au0 MPs played a pivotal role in enhancing the PL output of Yb3+ ions in the Li2O−HfO2−SiO2 glass ceramic. Thus, glass ceramics incorporating an optimal concentration of Au2O3 hold significant potential as materials for NIR lasers.

0D Pyramid‐intercalated 2D Bimetallic Halides with Tunable Electronic Structures and Enhanced Emission under Pressure

AbstractHybrid metal halides are emerging semiconductors as promising candidates for optoelectronics. The pursuit of hybridizing various dimensions of metal halides remains a desirable yet highly complex endeavor. By utilizing dimension engineering, a diverse array of new materials with intrinsically different electronic and optical properties has been developed. Here, we report a new family of 2D‐0D hybrid bimetallic halides, (C6N2H14)2SbCdCl9 ⋅ 2H2O (SbCd) and (C6N2H14)2SbCuCl9 ⋅ 2H2O (SbCu). These compounds adopt a new layered structure, consisting of alternating 0D square pyramidal [SbCl5] and 2D inorganic layers sandwiched by organic layers. SbCd and SbCu have optical band gaps of 3.3 and 2.3 eV, respectively. These compounds exhibit weak photoluminescence (PL) at room temperature, and the PL gradually enhances with decreasing temperature. Density functional theory (DFT) calculations reveal that SbCd and SbCu are direct gap semiconductors, where first‐principles band gaps follow the experimental trend. Moreover, given the different pressure responses of 0D and 2D components, these materials exhibit highly tunable electronic structures during compression, where a remarkable 11 times enhancement in PL emission is observed for SbCd at 19 GPa. This work opens new avenues for designing new layered bimetallic halides and further manipulating their structures and optoelectronic properties via pressure.

High-performance amplified spontaneous emission in inorganic CsPbBr3 perovskite thin films grown on engineered quartz substrates.

In this work, periodic rectangular arrays were fabricated on quartz substrates using the femtosecond laser ablation technique, on which inorganic cesium lead bromide thin films were grown using the spin coating method. Enhanced photoluminescence emission was investigated using a homebuilt confocal microscope, and increased light absorption due to the engineered structures was also measured. High-performance amplified spontaneous emission with typical narrow lasing emission peaks excited using a nanosecond laser centered at 266 nm was obtained. This work provides a method to modify the performance of optoelectrical devices, which helps develop light-emitting diodes, photodetectors, solar cells, and lasers.

Electron Donor, Acceptor, and Concentration-Dependent Quenching of Photoluminescent Carbon Nanodots

Carbon nanodots (CNDs) are 0D-carbon nanomaterials with distinct fluorescence properties. Due to the poor understanding of the fluorescent origin and its connection to the structural complexity of CNDs, the full potential in applications of CNDs is still in a stagnant stage. Herein, we present the photoluminescence properties of two CNDs prepared from di-ammonium citrate and tri-ammonium citrate. Synthesis of CNDs was done by pyrolysis of ammonium citrates at 180 °C and 40 h under ambient conditions. We monitored the pyrolysis process using thermogravimetric analysis (TGA) both under air and inert atmospheres, which allowed for the proposal of reaction stoichiometry and structural analyses of CNDs in combination with spectroscopic means. Both CNDs possess strong photoluminescence (PL) emissions at ∼450 nm upon excitation at 365 nm. Concentration-dependent PL emission kinetics were studied to reveal both nanoparticle-like behaviors of CNDs with the enhancement of PL emission upon dilution and aggregation-induced quenching of PL emission that is common for molecular fluorophores. Quenching of CNDs’ emission with the benzophenone as a triplet sensitizer or an acceptor and the dimethoxy benzene as a donor was also studied to present additional PL emission dynamics of CNDs in support of the proposed structure for CNDs. The extensive aggregation and stacking of the proposed CNDs structure were verified using molecular dynamics simulations.

Cation substitution induced highly symmetric crystal structure in cyan-green-emitting Ca2La1-xLuxHf2Al3O12:Ce3+ solid-solution phosphors with enhanced photoluminescence emission and thermal stability: Toward full-visible-spectrum white LEDs

Highly efficient cyan-green-emitting phosphors are urgently needed for high-color-quality full-visible-spectrum white light-emitting diodes (LEDs). Herein, we report on efficient near-ultraviolet-excited cyan-green-emitting Ca2La1-xLuxHf2Al3O12:Ce3+ (CLa1-xLuxHA:Ce3+) garnet phosphors, which are developed based on the solid-solution design of chemical cation substitution. All phosphor samples present a garnet crystal structure with the Ia3‾d space group; with increasing Lu3+ ions content, the lattice could be gradually contracted, along with a high symmetry as well as rigidity. Furthermore, under the 408 nm excitation, the cyan-green emissions of CLa1-xLuxHA:Ce3+ phosphors are progressively enhanced with a slight blue-shift, due to crystal field splitting and Stokes shift. Importantly, quantum efficiency and thermal stability performances are greatly improved by introducing smaller Lu3+ ions to replace the bigger La3+ ions, owing to the high rigidity structure with high symmetry. The optimized CLa0.5Lu0.5HA:Ce3+ phosphor exhibits an intense cyan-green emission band with high internal quantum efficiency of 76.4% and external quantum efficiency of 54.4%. Through employing the as-prepared CLa0.5Lu0.5HA:Ce3+ cyan-green phosphor, we have successfully fabricated a full-visible-spectrum LED device, demonstrating a bright warm-white light emission with an extremely high color rendering index (Ra = 98.0, R9 = 95.9, and R12 = 94.3) and low correlated color temperature (3497 K) under 100 mA driving current. This study not only reveals the correlation between the crystal structure evolution and luminescent properties of phosphor materials, but also provides new strategies for the design and development of novel efficient luminescent materials for high-quality full-visible-spectrum LED lighting.

Anomalous photoluminescence enhancement and resonance charge transfer in type-II 2D lateral heterostructures

Type-II band alignment can realize the efficient charge transfer and separation at the semiconductor heterointerface, which results in photoluminescence (PL) quenching. Recently, several researches demonstrated great enhancement of localized PL at the interface of type-II two-dimensional (2D) heterostructure. However, the dominant physical mechanism of this enhanced PL emission has not been well understood. In this work, we symmetrically study the exciton dynamics of type-II lateral heterostructures of monolayer MoS2 and WS2 at room temperatures. The strong PL enhancement along the one-dimensional (1D) heterointerface is associated with the trion emission of the WS2 shell, while a dramatic PL quenching of neutral exciton is observed on the MoS2 core. The enhanced quantum yield of WS2 trion emission can be explained by charge-transfer-enhanced photoexcited carrier dynamics, which is facilitated by resonance hole transfer from MoS2 side to WS2 side. This work sheds light on the 1D exciton photophysics in lateral heterostructures, which has the potential to lead to new concepts and applications of optoelectronic device.

Influence of Elevated Temperature on Color Centers in LiF Crystals and Their Photoluminescence

The radiation-induced photoluminescence (PL) of LiF has found its way into many applications for the detection and imaging of ionizing radiation. In this work, the influence of thermal treatment at temperatures up to 400 °C on absorption and PL emission spectra as well as fluorescent nuclear tracks in irradiated LiF crystals was investigated. It was found that carrying out PL measurements with the crystals kept at the temperature of about 80 °C leads to a considerable increase in luminescence emission of F3+ color centers at 525 nm. This enhancement of PL intensity allows for the microscopic imaging of the fluorescent nuclear tracks using only F3+ emission, which is not possible at room temperature. It was also found that heating the irradiated crystals before measurement at temperatures from 100 °C to 200 °C increases the concentration of F3+ centers. However, the related enhancement of PL emission is insufficient in terms of enabling the observation of the fluorescent tracks in this part of the spectrum. In the case of the main PL emission at 670 nm related to F2 centers, the thermal treatment at around 290 °C substantially increases the intensity of fluorescent tracks. This effect, however, was found to occur only at low fluences of alpha particles (up to about 109 cm-2); therefore, it is barely visible in the emission spectrum and not noticeable in the absorption spectrum.

Tailoring photoluminescence of WS2-microcavity coupling devices in broad visible range

Abstract Most of the previous TMDC-photon coupling devices were mainly based on A exciton due to its high oscillator strength and large exciton binding energy. Less effort has been focused on the modulation of the emission of B exciton and Rydberg states in TMDCs, especially in monolayer WS2. Here, we demonstrate that the photoluminescence (PL) emission of WS2-microcavity coupling devices can be tailored in a broad visible wavelength range (490 nm–720 nm). In contrast to the intrinsic PL emission of monolayer WS2, 25-fold enhanced B exciton emission and significant PL emission from the 2s Rydberg state can be observed. From the transient absorption (TA) measurements, the strongly coupled hybrid states based on B exciton can be remarkably fingerprinted. Furthermore, the strongly enhanced PL emission from the coupled B exciton has been demonstrated due to the strongly increased lower polariton (LP) state population and the internal conversion pathway being blocked in the strong coupling regime. Besides, the remarkable PL emission from the 2s Rydberg state is also revealed and confirmed by the additional ground state bleaching signal in TA spectra. These physical mechanisms about tailoring the PL emission in low dimensional TMDCs can provide significant references for constructing highly efficient optoelectronic devices.

Enhancing Photoluminescence Intensity and Spectral Bandwidth of Hybrid Nanofiber/Thin-Film Multilayer Tm3+-Doped SiO2-HfO2.

Multilayering of optical thin films is widely used for a range of purposes in photonic technology, but the development of nanofiber structures that can outperform thin films and nanoparticles in optical applications cannot simply be disregarded. Hybrid structures composed of Tm3+-doped SiO2-HfO2 in the form of nanofibers (NFs) and thin films (TFs) are deposited on a single substrate using the electrospinning and dip-coating methods, respectively. Ultrafine nanofiber strands with a diameter of 10-60 nm were fabricated in both single and multilayer samples. Enhanced photoluminescence emission intensity of about 10 times was attained at wavelengths of around 457, 512 and 634 nm under an excitation of 350 nm for NF-TF-NF* hybrid structures when compared with single-layered NF and TF structures. The arrangement of nanofibers and thin films in a multilayer structure influenced the luminescence intensity and spectral bandwidth. High transparency in the range of 75-95% transparency across the wavelength of 200-2000 nm was achieved, making it ideal for photonic application. Theoretical findings obtained through IMD software were compared with experimental results, and they were found to be in good agreement.

Enhanced optical emission at MoS2-WS2 heterostructure interface with n-N junction

Atomically thin transition metal dichalcogenide based heterostructures are of significant interest for the electronic and optoelectronic device applications. Growth of atomically thin heterostructures have gained remarkable importance due to the unusual electrical response and optical emission at the interface. Here, facile chemical vapour deposition growth of n-N type MoS2-WS2 heterostructure is demonstrated. Multifold enhancement in photoluminescence emission at the interface of MoS2-WS2 heterostructure with local excitonic amplifications arising at the interface is observed. The atomic level structure of interface has been investigated with the aid of aberration corrected scanning transmission electron microscopy. Electrical properties of MoS2-WS2 heterostructure with n-N semiconductor junction are systematically probed using micromanipulators interfaced with scanning electron microscope. Our microscopic and spectroscopic investigations along with electrical and optical responses at the interface contribute to the fundamental knowledge to empower the development of optical devices based on two dimensional heterostructures with enhanced emissions.

Suppression of Phase Transitions in Perovskite Thin Films through Cryogenic Electron Beam Irradiation.

Organic-inorganic hybrid perovskites (OIHPs) with superior optoelectronic properties have emerged as revolutionary semiconductor materials for diverse applications. A fundamental understanding of the interplay between the microscopic molecular-level structure and the macroscopic optoelectronic properties is essential to boost device performance toward theoretical limits. Here, we reveal the critical role of CH3NH3+ (MA) in the regulation of the physicochemical and optoelectronic properties of a MAPbI3 film irradiated by an electron beam at 130 K. The order-to-disorder transformation of the MA cation not only leads to a notably enhanced photoluminescence emission but also results in the suppression of the orthorhombic phase down to 85 K. Taking advantage of the regulation of MA cation dynamics, we demonstrate a perovskite photodetector with 100% photocurrent enhancement and long-term stability exceeding one month. Our study provides a powerful tool for regulating the optoelectronic properties and stabilities of perovskites and highlights potential opportunities related to the organic cation in OIHPs.

Bright and Photostable Fluorescent Metal Nanocluster Supraparticles from Invert Emulsions.

Fluorescent supraparticles of gold, silver and copper nanoclusters are synthesized by simply drying of invert emulsions, resulting in a dozen-fold increase in photoluminescence quantum yield (up to ≈80 %) and a significant improvement in photostability. The inhibition of the ligand twisting during the intramolecular charge transfer is found to be responsible for the enhancement, especially for the gold nanocluster supraparticles. This research provides a general, flexible, and easy method for producing highly luminescent and photostable metal nanocluster-based materials that promise practical applications in white-light-emitting diodes.

Asymmetric Broadening and Enhanced Photoluminescence Emission in ZnO Due to Electron–Phonon Coupling

Asymmetric Broadening and Enhanced Photoluminescence Emission in ZnO Due to Electron–Phonon Coupling