Light-emitting Technology Research Articles

Surface plasmon-mediated photoluminescence boost in graphene-covered CsPbBr3 quantum dots

The optical properties of graphene (Gr)-covered CsPbBr3 quantum dots (QDs) were investigated using micro-photoluminescence spectroscopy, revealing a remarkable three orders of magnitude enhancement in photoluminescence (PL) intensity compared to bare CsPbBr3 QDs. To elucidate the underlying mechanisms, we combined experimental techniques with density functional theory (DFT) calculations. DFT simulations showed that the graphene layer generates interfacial electrostatic potential barriers when in contact with the CsPbBr3 surface, impeding carrier leakage from perovskite to graphene and enhancing radiative recombination. Additionally, graphene passivates CsPbBr3 surface defect states, suppressing nonradiative recombination of photo-generated carriers. Our study also revealed that graphene becomes n-doped upon contact with CsPbBr3 QDs, activating its plasmon mode. This mode resonantly couples with photo-generated excitons in the perovskite. The momentum mismatch between graphene plasmons and free-space photons is resolved through plasmon scattering at Gr/CsPbBr3 interface corrugations, facilitating the observed super-bright emission. These findings highlight the critical role of graphene as a top contact in dramatically enhancing CsPbBr3 QDs’ PL. Our work advances the understanding of graphene-perovskite interfaces and opens new avenues for designing high-efficiency optoelectronic devices. The multifaceted enhancement mechanisms uncovered provide valuable insights for future research in nanophotonics and materials science, potentially leading to breakthroughs in light-emitting technologies.

Recent Advances in Perovskite-Based Flexible Electroluminescent Devices.

Perovskite-based flexible electroluminescent (EL) devices are emerging as promising candidates in the display field due to their exceptional optoelectronic properties and potential for cost-effective production. However, simultaneously achieving high EL performance, excellent flexibility and stretchability, robust mechanical strength, and diverse applications remains a significant challenge. In this review, we provide a comprehensive overview of the latest developments in perovskite-based flexible EL devices, covering both direct-current (DC) and alternating-current (AC) electroluminescent formats. Our discussion encompasses the materials, working principles, device architectures, failure mechanisms, optimization strategies, and practical applications. Through this review, we aim to deepen our understanding of the current challenges and future directions of perovskite-based flexible light-emitting technologies, hoping to facilitate their potential commercial applications.

Clinical use of lasers and energy-based devices in selected skin diseases

Introduction and purpose In recent years, there has been notable progress in the role of light-emitting technologies, including lasers and other energy-based devices, across various medical disciplines. Dermatology stands out as one of the prominent fields where laser treatments have gained significant popularity. In the clinical setting, a variety of laser types are utilized. A fundamental aspect of ensuring the safe use of laser devices involves comprehending their mechanisms at the tissue level. This knowledge enables practitioners to attain the desired outcomes effectively while minimizing the risk of complications. Lasers have demonstrated effectiveness in treating cutaneous vascular conditions because of their capacity to selectively target intravascular oxyhemoglobin. Rosacea, juvenile hemangioma, and port wine stains are among the vascular skin conditions for which laser therapy has shown notable success. Laser therapy is employed in treating hypertrophic scars, keloids, and acne scars because it facilitates the restructuring of the skin's architecture at the scar site, with the goal of minimizing its size and visibility. Laser therapy stands as the gold standard for removing tattoos. Materials and methods The methodology for conducting literature search involved utilizing medical subject headings terms to explore PubMed. Search terms included: “lasers”, “intense pulsed light”, “dermatology”, “rosacea”, “acne”, “scars”, “tattoo removal”. Conclusions Laser dermatological treatments are gaining popularity worldwide, driving new innovations and clinical applications. This review highlights the significant role and diverse clinical applications of lasers and intense pulsed light in dermatological practice. Improving the quality of skin in patients suffering from skin diseases can significantly increase their quality of life.

A thorough study of the efficiency of UV light-emitting technologies against coronaviruses

A thorough study of the efficiency of UV light-emitting technologies against coronaviruses

Advanced Light Source Technologies for Photodynamic Therapy of Skin Cancer Lesions.

Photodynamic therapy (PDT) is an increasingly popular dermatological treatment not only used for life-threatening skin conditions and other tumors but also for cosmetic purposes. PDT has negligible effects on underlying functional structures, enabling tissue regeneration feasibility. PDT uses a photosensitizer (PS) and visible light to create cytotoxic reactive oxygen species, which can damage cellular organelles and trigger cell death. The foundations of modern photodynamic therapy began in the late 19th and early 20th centuries, and in recent times, it has gained more attention due to the development of new sources and PSs. This review focuses on the latest advancements in light technology for PDT in treating skin cancer lesions. It discusses recent research and developments in light-emitting technologies, their potential benefits and drawbacks, and their implications for clinical practice. Finally, this review summarizes key findings and discusses their implications for the use of PDT in skin cancer treatment, highlighting the limitations of current approaches and providing insights into future research directions to improve both the efficacy and safety of PDT. This review aims to provide a comprehensive understanding of PDT for skin cancer treatment, covering various aspects ranging from the underlying mechanisms to the latest technological advancements in the field.

High-resolution light-emitting devices for display applications

As carriers of visual information, displays play an indispensable role in our daily life. In recent years, high-resolution (HR) self-emissive displays have been rapidly developed because of the expanding market demand for micro-display products; consequently, research on the improvement of display resolution, material and device structure optimization, the design and development of drive circuits, and various applications of HR display technology has significantly increased. However, there is no comprehensive review of HR light-emitting devices. This review focuses on HR light-emitting technologies. The main contents of the review are as follows: (1) methods for fabricating HR light-emitting devices; (2) processes for fabricating self-emissive displays and other potential fine patterning techniques for the same purpose; (3) the advantages and limitations of these processes; (4) the challenges associated with HR displays. This review can serve as a valuable reference for the development of the mi-crodisplay industry and for studies on microdisplays.

Near-Infrared Light-Emitting Diodes Based on RoHS-Compliant InAs/ZnSe Colloidal Quantum Dots.

We demonstrate efficient, stable, and fully RoHS-compliant near-infrared (NIR) light-emitting diodes (LEDs) based on InAs/ZnSe quantum dots (QDs) synthesized by employing a commercially available amino-As precursor. They have a record external quantum efficiency of 5.5% at 947 nm and an operational lifetime of ∼32 h before reaching 50% of their initial luminance. Our findings offer a new solution for developing RoHS-compliant light-emitting technologies based on Pb-free colloidal QDs.

Directional modulated light-emitting technology based on airborne display

ABSTRACT High-quality airborne display benefits pilots of making correct interpretation and operation in time, and avoids from moving body due to the unclear transmission of flight data which may lead to flying risk. A directional modulated light-emitting technology based on airborne display is proposed in this paper which can be used on Diamond DA42 New Generation aircraft. Using the proposed technology, a composite optical film with micro-structure is designed which can realise the redistribution of light intensity according to the viewing demand. A collimated display is introduced to reduce the colour shift. When the optical film is attached on a collimated display, the incident light of small viewing angles can be directionally modulated and concentrated to the large viewing angles which are just effective pilot and co-pilot viewing angles. The calculation results show that the brightness of airborne display on two pilots’ viewing angles can be increased by 38.9% and 58.7% respectively after using the proposed technology. Meanwhile, the emergent angles from the collimated display are smaller than both two pilots’ viewing angles, so the proposed optical film is beneficial to reduce the colour shift and resulting in a better display quality.

Identifying Highly Photoelectrochemical Active Sites of Two Au21 Nanocluster Isomers toward Bright Near-Infrared Electrochemiluminescence.

Thus far, no correlation between nanocluster structures and their electrochemiluminescence (ECL) has been identified. Herein, we report how face-centered-cubic and hexagonal close-packed structures of two Au21(SR)15 nanocluster isomers determine their chemical reactivity. The relationships were explored by means of ECL and photoluminescence spectroscopy. Both isomers reveal unprecedented ECL efficiencies in the near-infrared region, which are >10- and 270-fold higher than that of standard Ru(bpy)32+, respectively. Photoelectrochemical reactivity as well as ECL mechanisms were elucidated based on electrochemistry, spooling photoluminescence, and ECL spectroscopy, unfolding the three emission enhancement origins: (i) effectively exposed reactive facets available to undergo electron transfer reactions; (ii) individual excited-state regeneration loops; (iii) cascade generations of various exited states. Indeed, these discoveries will have immediate impacts on various applications including but not limited to single molecular detection as well as photochemistry and electrocatalysis toward clean photon-electron conversion processes such as light-harvesting and light-emitting technologies.

(INVITED) Lighting-up nanocarbons through hybridization: Optoelectronic properties and perspectives

In recent years, a plethora of material systems have been designed and prepared to increase the performance of light harvesting and light-emitting technologies, and to develop new and attractive applications. Limitations of state-of-the-art devices based on organics (both conjugated polymers or small molecules/oligomers) derive largely from material stability issues after prolonged operation. This challenge could be tackled by leveraging the enhanced stability of carbon nanostructures (CNSs, including carbon nanotubes and the large family of graphene-based materials) in carefully designed nano-hybrid or nano-composite architectures to be integrated within photo-active layers, paving the way to the exploitation of these materials in contexts in which their potential has not been yet fully revealed. In this review, we discuss the theoretical and experimental background behind CNSs hybridization with other materials for the establishment of novel optoelectronic properties and provide an overview of the existing examples in the literature that allow to forecast interesting future perspectives for use in real devices.

Germanium-lead perovskite light-emitting diodes

Reducing environmental impact is a key challenge for perovskite optoelectronics, as most high-performance devices are based on potentially toxic lead-halide perovskites. For photovoltaic solar cells, tin-lead (Sn–Pb) perovskite materials provide a promising solution for reducing toxicity. However, Sn–Pb perovskites typically exhibit low luminescence efficiencies, and are not ideal for light-emitting applications. Here we demonstrate highly luminescent germanium-lead (Ge–Pb) perovskite films with photoluminescence quantum efficiencies (PLQEs) of up to ~71%, showing a considerable relative improvement of ~34% over similarly prepared Ge-free, Pb-based perovskite films. In our initial demonstration of Ge–Pb perovskite LEDs, we achieve external quantum efficiencies (EQEs) of up to ~13.1% at high brightness (~1900 cd m−2), a step forward for reduced-toxicity perovskite LEDs. Our findings offer a new solution for developing eco-friendly light-emitting technologies based on perovskite semiconductors.

Bifacial Color-Tunable Electroluminescent Devices.

Alternate current electroluminescent (ACEL) devices provide a range of interesting properties, such as facile large-area processability, mechanical flexibility, and outstanding resilience, when compared with other large-area light-emitting technologies. To widen the scope of possible applications for ACEL devices, color tunability and white light emission are desirable. Here, we introduce a novel three-terminal device architecture based on two monolithically stacked ACEL devices (e.g., orange and blue) that allows for color tunability via independent operation of the subdevices. The tandem devices comprise semitransparent bottom and top electrodes based on networks of silver nanowires, which endow the tandem ACEL device with bifacial Janus-type emission. We provide a detailed analysis of the sources of optical losses in single and tandem ACEL devices. Our novel device concept enables novel facets of applications for ACEL in signage and lighting.

Materials Design and Optimization for Next-Generation Solar Cell and Light-Emitting Technologies.

We review some of the most potent directions in the design of materials for next-generation solar cell and light-emitting technologies that go beyond traditional solid-state inorganic semiconductor-based devices, from both the experimental and computational standpoints. We focus on selected recent conceptual advances in tackling issues which are expected to significantly impact applied literature in the coming years. Specifically, we consider solution processability, design of dopant-free charge transport materials, two-dimensional conjugated polymeric semiconductors, and colloidal quantum dot assemblies in the fields of experimental synthesis, characterization, and device fabrication. Key modeling issues that we consider are calculations of optical properties and of effects of aggregation, including recent advances in methods beyond linear-response time-dependent density functional theory and recent insights into the effects of correlation when going beyond the single-particle ansatz as well as in the context of modeling of thermally activated fluorescence.

Zone-Folded Longitudinal Acoustic Phonons Driving Self-Trapped State Emission in Colloidal CdSe Nanoplatelet Superlattices

Colloidal CdSe nanoplatelets (NPLs) have substantial potential in light-emitting applications because of their quantum-well-like characteristics. The self-trapped state (STS), originating from strong electron-phonon coupling (EPC), is promising in white light luminance because of its broadband emission. However, achieving STS in CdSe NPLs is extremely challenging because of their intrinsic weak EPC nature. Herein, we developed a strong STS emission in the spectral range of 450-600 nm by building superlattice (SL) structures with colloidal CdSe NPLs. We demonstrated that STS is generated via strong coupling of excitons and zone-folded longitudinal acoustic phonons with formation time of ∼450 fs and localization length of ∼0.56 nm. The Huang-Rhys factor, describing the EPC strength in SL structure, is estimated to be ∼19.9, which is much larger than that (∼0.1) of monodispersed CdSe NPLs. Our results provide an in-depth understanding of STS and a platform for generating and manipulating STS by designing SL structures.

Benzo crown ether functionalized conjugated polyfluorenes with anthracene fragment for sustainable light-emitting device technology

Dibenzo crown ether-substituted units of fluorene and acene-bearing copolymers have been successfully synthesized. FTIR, 1H and 13C NMR spectroscopy, DSC, TGA and GPC were used to characterize the resulting copolymers (P1–P5). With fascinating quantum yield, the polymers showed large band gaps. With a polydispersity index of 1.58–2.21, these polymers showed a higher molecular weight (16,080–20,480). Strong thermal stability was indicated by DSC and TGA studies. The cyclic voltammetry analysis found that these polyfluorenes were stable in the range of 0.43–0.53 eV under redox conditions with HOMO and LUMO. For light-emitting materials, thermal stability and emission studies display strong results that are desirable.

Room-Temperature Phosphorescence and Low-Energy Induced Direct Triplet Excitation of Alq3 Engineered Crystals.

Crystal engineering is a practical approach for tailoring material properties. This approach has been widely studied for modulating optical and electrical properties of semiconductors. However, the properties of organic molecular crystals are difficult to control following a similar engineering route. In this Letter, we demonstrate that engineered crystals of Alq3 and Ir(ppy)3 complexes, which are commonly used in organic light-emitting technologies, possess intriguing functional properties. Specifically, these structures not only process efficient low-energy induced triplet excitation directly from the ground state of Alq3 but also can show strong emission at the Alq3 triplet energy level at room temperatures. We associate these phenomena with local deformations of the host matrix around the guest molecules, which in turn lead to a stronger host-guest triplet-triplet coupling and spin-orbital mixing.

Directed Energy Transfer from Monolayer WS2 to Near-Infrared Emitting PbS-CdS Quantum Dots.

Heterostructures of two-dimensional (2D) transition metal dichalcogenides (TMDs) and inorganic semiconducting zero-dimensional (0D) quantum dots (QDs) offer useful charge and energy transfer pathways, which could form the basis of future optoelectronic devices. To date, most have focused on charge transfer and energy transfer from QDs to TMDs, that is, from 0D to 2D. Here, we present a study of the energy transfer process from a 2D to 0D material, specifically exploring energy transfer from monolayer tungsten disulfide (WS2) to near-infrared emitting lead sulfide–cadmium sulfide (PbS–CdS) QDs. The high absorption cross section of WS2 in the visible region combined with the potentially high photoluminescence (PL) efficiency of PbS QD systems makes this an interesting donor–acceptor system that can effectively use the WS2 as an antenna and the QD as a tunable emitter, in this case, downshifting the emission energy over hundreds of millielectron volts. We study the energy transfer process using photoluminescence excitation and PL microscopy and show that 58% of the QD PL arises due to energy transfer from the WS2. Time-resolved photoluminescence microscopy studies show that the energy transfer process is faster than the intrinsic PL quenching by trap states in the WS2, thus allowing for efficient energy transfer. Our results establish that QDs could be used as tunable and high PL efficiency emitters to modify the emission properties of TMDs. Such TMD-QD heterostructures could have applications in light-emitting technologies or artificial light-harvesting systems or be used to read out the state of TMD devices optically in various logic and computing applications.

Wurtzite quantum well structures under high pressure

Quantum well systems based on semiconductors with the wurtzite crystalline structure have found widespread applications in photonics and optoelectronic devices, such as light-emitting diodes, laser diodes, or single-photon emitters. In these structures, the radiative recombination processes can be affected by (i) the presence of strain and polarization-induced electric fields, (ii) quantum well thickness fluctuations and blurring of a well–barrier interface, and (iii) the presence of dislocations and native point defects (intentional and unintentional impurities). A separate investigation of these phenomena is not straightforward since they give rise to similar effects, such as a decrease of luminescence efficiency and decay rate, enhancement of the Stokes shift, and strong blueshift of the emission with increasing pump intensity. In this Perspective article, we review the usefulness of measurements of the quantum well luminescence as a function of the hydrostatic pressure for both scientific research and the development of light-emitting technologies. The results presented here show that high-pressure investigations combined with ab initio calculations can identify the nature of optical transitions and the main physical factors affecting the radiative efficiency in quantum well systems. Finally, we will discuss an outlook to the further possibilities to gain new knowledge about the nature of recombination processes in quantum wells using high-pressure spectroscopy.

Template Stripping of Perovskite Thin Films for Dry Interfacing and Surface Structuring.

Combining excellent optoelectronic properties with the benefits of solution processability, metal-halide perovskites are promising materials for photovoltaic and light-emitting technologies. To facilitate the integration of perovskite thin films into optoelectronic devices, a need exists for simple and efficient fabrication methods. Here, we present a template-stripping technique to produce ultraflat and flexible perovskite thin films. We apply a one-step spin-coating procedure to produce high-quality CH3NH3PbBr3 perovskite thin films on top of ultraflat silicon templates. These films can be mechanically cleaved from the template using a polymer adhesive to reveal the ultraflat perovskite surfaces. We demonstrate how the flatness and flexibility of the template-stripped films enable new processing strategies based on dry interfacing, by interfacing them with plasmonic hole arrays. Moreover, we show that by using prepatterned silicon templates, structured perovskite surfaces can be produced with feature sizes down to a micrometer.

Recent Progress on Cesium Lead Halide Perovskites for Photodetection Applications

Recently, metal halide perovskites have attracted tremendous attention because of the unprecedented development in the research field of optoelectronic applications. Among the perovskites, all-inorganic halide perovskites (IHPs), especially the cesium lead halide type, show great potential for light-emitting devices because of their excellent optoelectronic properties, such as an ultrahigh photoluminescence quantum yield, high absorption coefficient, and large carrier mobility. Moreover, recent advancements have demonstrated that the extraordinary optical and electrical properties combined with a high chemical stability and facile synthesis make IHPs promising candidates for next-generation high-performance photodetectors (PDs) beyond light-emitting technologies. In this Review, the syntheses of IHPs with different forms, as well as their fundamental optical and electronic properties, are first summarized and compared. Thereafter, we focus on the recent progress of IHP-based PDs working with different wavelengths, covering the infrared, visible, ultraviolet, and gamma regions. Then, the challenges and opportunities facing the field of PDs based on IHPs are discussed. Finally, a brief outlook is given for the future development of IHP-based PDs.