Enhancement Of Quantum Efficiency Research Articles

Enhanced photoluminescence characteristics in Mg doped Alq3: An insight into doping mechanism

The present paper deals with the investigations on the effect of Mg doping on the structural and photophysical properties of Alq3 thin films. Mg doped Alq3 powders, with varying Mg concentrations, are synthesized using co-precipitation method and their thin films are deposited using vacuum evaporation method. These films are subjected to different analytical analyses to study the effect of Mg doping on the structural and photophysical properties of Alq3. It has been observed that Mg is attached at the central part of the Alq3 molecules making bonds with Al, N and O atoms. In this process, Mg atoms transfer electrons to Alq3 molecules and increases the electron density in its highest occupied molecular orbital (HOMO). Increased HOMO electron density in Mg doped Alq3 results in the improvement in its photoluminescence characteristics. Highest photoluminescent characteristics are observed for Mg doped Alq3 having 1.5 % (by mole) Mg which shows almost 2-fold enhancement in photoluminescence quantum efficiency (PLQY) and 3-fold enhancement in radiative decay rate. The results obtained in this work suggest that Mg doped Alq3 films may be integrated in high performing organic light emitting devices.

Epitaxial analysis of GaInP/AlGaInP red light-emitting diodes with ternary AlGaP quantum barriers for quantum efficiency enhancement

We have numerically analyzed Gallium Indium Phosphide (GaInP)/Aluminum Gallium Indium Phosphide (AlGaInP) red light-emitting diodes (LEDs) by utilizing ternary Aluminum Gallium Phosphide (AlGaP) quantum barriers instead of the conventional quaternary AlGaInP quantum barriers. The simulation findings show that the use of AlGaP quantum barriers in AlGaInP red light-emitting diodes leads to a significant increase in both electron and hole concentration in the quantum wells which in turn enhances the rate of radiative recombination compared to conventional (reference) red light-emitting diodes. Furthermore, the proposed LEDs have a substantial decline in efficiency droop from 38% to 32%.

Asymmetric Potential Model of Two-Dimensional Imine Covalent Organic Frameworks with Enhanced Quantum Efficiency for Photocatalytic Water Splitting.

Two-dimensional (2D) covalent organic frameworks (COFs) assembled using building blocks have been widely employed in photocatalysis due to their customizable optoelectronic characteristics and porous structure, which facilitate charge carrier and mass movement. Nevertheless, the development of COF photocatalysts encounters a continuous obstacle in enhancing the efficiency of photocatalysis, impeded by a limited comprehension of the orbital interaction between molecular fragments and linkers. In this study, we present a model that examines the interaction between molecular fragments in an imine-based COF at the frontier molecular orbital level, enabling us to comprehend the impact of manipulating linkers on light adsorption, exciton efficiency, and catalytic activity. Our findings demonstrate that altering the connecting orientation of 14 R-C=N-R imine linkers in 2D COFs can enhance solar-to-hydrogen (STH) efficiency under visible light from 2.76% to 4.24%. This research has the potential to provide a valuable model for refining photocatalysts with enhanced photocatalytic performance.

Plasmonic utilization of silver nanoparticles in PM6:Y7 organic solar cell

Silver nanoparticles (AgNPs) are employed to utilize plasmonic effects in PM6:Y7 organic solar cell. Such enables utilization of wavelengths ranging from 400–490 nm and resonance tuning toward longer wavelengths. Inverted structure is employed with AgNPs incorporated into zinc oxide (ZnO) layer. 5–15% volume ratio concentrations of AgNPs were used. The results obtained indicated a 12.97% power conversion efficiency for AgNPs with 10% concentration in comparison to the device without AgNP incorporation. Finite-difference time-domain method (FDTD) simulation of AgNP indicated forward scattering as the most dominant mechanism for external quantum efficiency (EQE) enhancements for wavelengths ranging from 500-900nm.

Synergistic strategies of metallization and redox coupling to enhance the quantum yield and recyclability of porphyrin COF

Enhancing the quantum efficiency of photocatalytic reactions and recyclability of photocatalysts are crucial for the practical applications of photocatalytic technology. In this study, a mechanical grinding method was employed to prepare porphyrin covalent organic framework (Por-COF) and metalloporphyrin covalent organic frameworks (MPor-COF, M = Zn, Fe). These COFs were evaluated for their photocatalytic and recycling performances under visible light. ZnPor-COF exhibited a significant enhancement in quantum efficiency compared to Por-COF, with efficiency increases of 31.8 %, 3.0 %, and 11.5 % for individual reduction, individual oxidation, and simultaneous redox reactions, respectively. Notably, when ZnPor-COF underwent simultaneous redox reactions with oxidation and reduction efficiencies above 80 %, the number of recycles increased from 3 to 10 times compared to Por-COF. This synergistic strategy of metallization and redox coupling improved the photocatalytic and recycling performance of Por-COF. Experimental and theoretical investigations revealed that the introduction of metal ions enhance light response, altere energy levels, reduce carrier separation distance, and improve carrier separation performance. Simultaneous oxidation and reduction reactions effectively mitigated photocorrosion, enhancing stability and carrier utilization efficiency. This research provides valuable insights for advancing porphyrin-based COF photocatalytic technology.

Water-Oil Interfacial Synthesis of Two-Dimensional Colloidal Lead-Iodide Perovskites with Enhanced Efficiency and Stability.

Two-dimensional Ruddlesden-Popper perovskites L2PbI4 (L = alkylammonium cation) (RPPs) have attracted significant attention due to their unique excitonic characteristics. However, their ultrafast reaction dynamics exacerbates the structural distortion of the inorganic framework, leading to severe deterioration in photoluminescence. Here, we propose a water-oil interfacial synthesis approach to achieve controlled growth of the RPPs nanosheets. By segregating Pb and I precursors in two immiscible solvents, the nucleation and growth of RPPs are prolonged to the minute level. L2PbI4 nanosheets terminated with various alkylammonium are synthesized, and the factors influencing the growth kinetics of RPPs nanosheets are investigated. The resulting (PEA)2PbI4 nanosheets exhibit a 3.6-time enhancement in quantum efficiency and 3.2-time improvement photostability compared to those synthesized using the classical recrystallization method. A white light-emitting diode based on (HDA)2PbI4 nanosheets is fabricated, achieving a color gamut of 119.7% of the NTSC display standards. This innovative approach offers a new method for the controlled growth of 2D RPPs with improved optical quality and stability.

Mn4+, Cr3+ Co‐doped K2LiGaF6 Phosphors with Bright Near‐Infrared Luminescence

AbstractIn this study, Cr3+‐doped and Mn4+‐Cr3+ co‐doped double perovskite fluoride phosphors K2LiGaF6 are prepared using a simple hydrothermal method. High‐efficiency near‐infrared (NIR) emission near 762 nm is obtained under blue‐light excitation, and the co‐doping effect of Mn4+ on the NIR luminescence properties of Cr3+ is studied. Compared with the Cr3+ single‐doped phosphor, Mn4+, and Cr3+ co‐doped K2LiGaF6 exhibit a sharp increase of 129% in NIR emission, an enhancement in the internal quantum efficiency from 82.5% to 90.0%, and an enhancement in the thermal stability at 425 K from 85.0% to 90.7%. The encapsulated NIR phosphor‐converted light‐emitting diode device at 300 mA exhibits a photoelectric conversion efficiency of 15.3%. These values exceed most previously reported results. This study provides a new approach for enhancing the luminescence properties of Cr3+‐doped fluoride NIR phosphors.

Broadband near infrared emission in Cr3+,Yb3+, Li+ tri-doped In2TeO6

Cr3+ near infrared (NIR) emission is witnessed in tellurite compound for the first time. Broadband emission that peaks at 840 nm and has 157 nm of full width at half maxima (FWHM) appears in the Cr3+ doped In2TeO6 phosphor when excited at 455 nm. Further introduction of Li+ ions into the In2TeO6 can distort the octahedral environment of the doped Cr3+ ions, resulting in 4 times enhancement in luminescence intensity and a 1.75-fold enhancement in internal quantum efficiency (IQE). Moreover, the FWHM increases to 282 nm in the In2TeO6: Cr3+,Li+,Yb3+ phosphor induced by the Cr3+ to Yb3+ energy transfer. LED device utilizing this NIR phosphor has been constructed. At 150 mA drive current, the optoelectrical efficiency is 11.189 % and the NIR output power is 50.72 mW. The In2TeO6: Cr3+,Li+,Yb3+phosphor exhibits enormous potential in NIR phosphor-converted LED (pc-LED).

Determining Factors to Understand the External Quantum Efficiency Values: Study Carried Out with Copper(I)-I and 1,2-Bis(4-pyridyl)ethane Coordination Polymers as Downshifters in Photovoltaic Modules.

Downshifters refer to compounds with the capacity to absorb UV photons and transform them into visible light. The integration of such downshifters has the potential to improve the efficiency of commercial photovoltaic modules. Initially, costly lanthanide derivatives and organic fluorescent dyes were introduced, resulting in a heightened module efficiency. In a novel research direction guided by the same physicochemical principles, the utilization of copper(I) coordination compounds is proposed. This choice is motivated by its simpler and more economical synthesis, primarily due to copper being a more abundant and less toxic element. Our proposal involves employing 1,2-bis(4-pyridyl) ethane (bpe), an economically viable commercial ligand, in conjunction with CuI to synthesize coordination polymers: [CuI(bpe)]n(1), [Cu3I3(bpe)3]n(2), and [CuI(bpe)0.5]n(3). These polymers exhibit the ability to absorb UV photons and emit light within the green and orange spectra. To conduct external quantum efficiency studies, the compounds are dispersed on glass and then encapsulated with ethylene vinyl acetate through heating to 150 °C. Interestingly, during these procedural steps, the solvents and temperatures employed induce a phase transformation, which has been thoroughly examined through both experimental analysis and theoretical calculations. The outcomes of these studies reveal an enhancement in external quantum efficiency with [Cu3I3(bpe)3]n(2), at a cost significantly lower (between 340 and 350 times) than that associated with lanthanide DS complexes.

Hollow Microcavity Electrode for Enhancing Light Extraction.

Luminous efficiency is a pivotal factor for assessing the performance of optoelectronic devices, wherein light loss caused by diverse factors is harvested and converted into the radiative mode. In this study, we demonstrate a nanoscale vacuum photonic crystal layer (nVPCL) for light extraction enhancement. A corrugated semi-transparent electrode incorporating a periodic hollow-structure array was designed through a simulation that utilizes finite-difference time-domain computational analysis. The corrugated profile, stemming from the periodic hollow structure, was fabricated using laser interference lithography, which allows the precise engineering of various geometrical parameters by controlling the process conditions. The semi-transparent electrode consisted of a 15 nm thick Ag film, which acted as the exit mirror and induced microcavity resonance. When applied to a conventional green organic light-emitting diode (OLED) structure, the optimized nVPCL-integrated device demonstrated a 21.5% enhancement in external quantum efficiency compared to the reference device. Further, the full width at half maximum exhibited a 27.5% reduction compared to that of the reference device, demonstrating improved color purity. This study presents a novel approach by applying a hybrid thin film electrode design to optoelectronic devices to enhance optical efficiency and color purity.

Direct Population of Triplet States for Efficient Organic Afterglow through the Intra/Intermolecular Heavy-Atom Effect.

Organic afterglow is a fascinating phenomenon with exceptional applications. However, it encounters challenges such as low intensity and efficiency, and typically requires UV-light excitation and facile intersystem crossing (ISC) due to its spin-forbidden nature. Here, we develop a novel strategy that bypasses the conventional ISC pathway by promoting singlet-triplet transition through the synergistic effects of the intra/intermolecular heavy-atom effect in aromatic crystals, enabling the direct population of triplet excited states from the ground state. The resulting materials exhibit a bright organic afterglow with a remarkably enhanced quantum efficiency of up to 5.81%, and a significantly increased organic afterglow lifetime of up to 157 microseconds under visible light. Moreover, given the high-efficiency visible-light excitable organic afterglow emission, the potential application is demonstrated in lifetime-resolved, color-encoded, and excitation wavelength-dependent pattern encryption. This work demonstrates the importance of the direct population method in enhancing the organic afterglow performance and red-shifting the excitation wavelength, and provides crucial insights for advancing organic optoelectronic technologies that involve triplet states.

Ordered Phase Distribution of Quasi‐2D Perovskites Controlled by a Supramolecular Approach Enables Efficient Blue Light‐Emitting Diodes

AbstractQuasi‐2D perovskites demonstrate exceptional luminescent properties, mainly attributed to heightened radiative recombination facilitated by the energy transfer process among spontaneous quantum‐well structures featuring varied n‐value distributions. However, the rapid crystallization process often induces uncontrolled variations in phase composition, characterized by distinct “n” values, leading to suboptimal energy transfer efficiency. In this study, an innovative supramolecular strategy utilizing cryptand is introduced as an additive to regulate the phase distribution within quasi‐2D perovskite films. Cryptand effectively inhibited the aggregation of PEA+ and the formation of unsaturated Pb‐X coordination compounds, thereby suppressing the generation of low‐“n” phases. This intervention resulted in a continuous series of ordered intermediate phases with higher “n” values. The graded electronic structure facilitated efficient energy transfer from low‐“n” to high‐“n” phases, promoting effective radiation recombination. As a result, the optimized PeLEDs emitting at 490 nm demonstrated a remarkable external quantum efficiency (EQE) enhancement to 10.16%, compared to the reference device with an EQE of 2.33%. The device also exhibited impressive spectral and operational stability. The findings establish a viable strategy for precise phase distribution regulation in quasi‐2D perovskites, offering great potential for high‐performance blue PeLEDs.

Breaking Through the Luminescence Stability Bottleneck of Oxyfluoride Phosphor for Sun‐Like Led Lighting

AbstractSunlight like optical source is the primary objective of healthy lighting. In contrast, achieving full spectrum lighting with high stability remains challenging, mostly due to the scarcity of purple chip‐pumped cyan‐green phosphors and their inherent emission instability. In this study, a novel strategy is presented that realizes simultaneous enhancements in both humidity stability (increased by 2.9 times) and luminescence quantum efficiency (enhanced by 1.5 times) for cyan‐emitting Sr3AlO4F:Ce3+ phosphor by employing Si/N doping. Theoretical modelling shows that these improvements are attributed to the regulation of energy bands and structural rigidity as well as modulation of the ionicity of chemical bonds. Furthermore, blending the other violet chip‐pumped phosphors, sun‐like LEDs that accurately replicate solar spectra in different times of the day with an optimal color rendering index of 99 is successfully engineered. Moreover, the universality of this strategy on other oxyfluoride phosphors has also been validated. This groundbreaking outcome offers a practical solution to overcome the inherent luminescence stability limitations in oxyfluoride phosphors, thus catalyzing the application of these cyan‐green candidates in sun‐like LED lighting.

Enhancement of the internal quantum efficiency in strongly coupled P3HT-C60 organic photovoltaic cells using Fabry–Perot cavities with varied cavity confinement

Abstract The short exciton diffusion length in organic semiconductors results in a strong dependence of the conversion efficiency of organic photovoltaic (OPV) cells on the morphology of the donor-acceptor bulk-heterojunction blend. Strong light–matter coupling provides a way to circumvent this dependence by combining the favorable properties of light and matter via the formation of hybrid exciton–polaritons. By strongly coupling excitons in P3HT-C60 OPV cells to Fabry–Perot optical cavity modes, exciton-polaritons are formed with increased propagation lengths. We exploit these exciton–polaritons to enhance the internal quantum efficiency of the cells, determined from the external quantum efficiency and the absorptance. Additionally, we find a consistent decrease in the Urbach energy for the strongly coupled cells, which indicates the reduction of energetic disorder due to the delocalization of exciton–polaritons in the optical cavity.

Stoke's shift and quantum efficiency enhancement in fluorescent coumarin aldehyde (HMCA) dye-conjugated chitosan matrix for optoelectronic applications

A greenish-yellow emissive fluorescent coumarin aldehyde conjugated chitosan matrix was prepared by performing a Schiff base reaction between 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde (HMCA) and chitosan. The newly formed imine linkage was confirmed by the appearance of an absorption band at 1641 cm−1 in the IR spectrum and also supported by the solid-state 13C-NMR with cross polarisation magic angle spinning (CPMAS) method. The molecular weight of the HMCA-conjugated chitosan matrix was augmented with an increase in the HMCA concentration. The SEM images unveiled crystallite aggregates in the chitosan matrix and the improved crystallinity was witnessed in the PXRD result. The chemically conjugated chitosan film unveiled a larger Stoke's shift value of 183–224 nm which was just 50–130 nm in pure HMCA. The conjugate material could overcome the self-absorption issue associated with the coumarin aldehyde. The coumarin aldehyde exhibited dual emission at 390 nm and 440 nm but it was shifted to 520 nm with single emission upon reaction with chitosan. The observed redshift could be assigned for the formation of static excimer that resulted from the chitosan backbone containing pendant chromophore (coumarin dye) which could interact with another neighbouring chromophoric group of the same chain or different chain creating a ground-state stable dimer. The emission of conjugate material shifted from blue to greenish yellow region with a higher quantum yield of 30.21 % compared to 8.57 % of HMCA alone. The calculated indirect band gap of 2.25–2.34 and the optimum refractive index suggested the potential optoelectronic applications of HMCA-conjugated chitosan as an OLED Material.

Exceptional optical performance of the zero-dimensional hybrid cuprous halide ETPA2Cu2I4 as an X-ray scintillator

The crystal structure, enhanced quantum efficiency and application of [C11H26N]2Cu2I4 in the field of high-energy detection are presented.

Strain modulation effect of superlattice interlayer on InGaN/GaN multiple quantum well

The strong piezoelectric field in InGaN/GaN heterostructure quantum wells severely reduces the light emission efficiency of multiple quantum well (MQW) structures. To address this issue, a strain modulation interlayer is commonly used to mitigate the piezoelectric polarization field and improve the luminescence performance of the devices. To investigate the influence and mechanism of strain modulation in the InGaN/GaN superlattice (SL), epitaxial wafers with an n-type InGaN/GaN SL interlayer sample, and their corresponding control samples are prepared. The measured temperature-dependent photoluminescence (PL) spectra of the epitaxial wafers, show that the introduction of an SL interlayer leads to a shorter-wavelength emission and enhancement of internal quantum efficiency. As the temperature increases, a blue shift of the PL peak is observed. However, for the sample with an SL interlayer, the blue shift of the PL peak with temperature increasing is relatively small. Electroluminescence (EL) experiments indicate that the introduction of an SL interlayer significantly increases the integrated intensity of the EL peak and reduces its full width at half maximum. These phenomena collectively indicate that the incorporation of a superlattice interlayer can partly suppress the quantum-confined Stark effect (QCSE) that affects the light emission efficiency. Theoretical calculations show that the introduction of a superlattice strain layer before growing an active multiple quantum well can weaken the polarization-induced built-in electric field in the active quantum well, reduce the tilt of the energy band in the multiple quantum well active region, increase the overlap of electron and hole wave functions, enhance the emission probability, shorten the radiative recombination lifetime, and promote competition between radiative recombination and non-radiative recombination, thereby achieving higher recombination efficiency and improving light emission intensity. This study provides experimental and theoretical evidence that the strain modulation SL interlayer can effectively improve the device performance and offer guidance for optimizing the structural design of devices.

Aqueous Solution Enhanced Room Temperature Phosphorescence through Coordination-Induced Structural Rigidity.

Achieving aqueous solution enhanced room temperature phosphorescence (RTP) is critical for the applications of RTP materials in solution phase, but which faces a great challenge. Herein, for the first time, a strategy of coordination-induced structural rigidity is proposed to achieve enhanced quantum efficiency of aluminum/scandium-doped phosphorescent microcubes (Al/Sc-PMCs) in aqueous solution. The Al/Sc-PMCs in a dry state exhibit a nearly invisible blue RTP. However, they emit a strong RTP emission in aqueous solution with a RTP intensity increase of up to 22.16-times, which is opposite to common solution-quenched RTP. The RTP enhancement mechanism is attributed to the abundant metal sites (Al3+ and Sc3+ ions) on the Al/Sc-PMCs surface that can tightly combine with water molecules through the strong coordination. Subsequently, these coordinated water molecules as the bridging agent can bind with surface groups by hydrogen bonding interaction, thereby rigidifying chemical groups and inhibiting their motions, resulting in the transition from the nonradiative decay to the radiative decay, which greatly enhances the RTP efficiency of the Al/Sc-PMCs. This work not only develops a coordination rigidity strategy to enhance RTP intensity in aqueous solution, but also constructs a phosphorescent probe to achieve reliable and accurate determination of analyte in complex biological matrices.

External Quantum Efficiency Enhancement of InGaN-Based Quantum Dot Green Micro-Light-Emitting Diode Arrays by Fabricating Full-A-Sided Triangular Mesa

External Quantum Efficiency Enhancement of InGaN-Based Quantum Dot Green Micro-Light-Emitting Diode Arrays by Fabricating Full-A-Sided Triangular Mesa

UV/ visible/ NIR sensitized enhanced green luminescence of a newly synthesized salicylic acid coated Tb3+ and Yb3+ ions doped Y2O3 nano-composite phosphor: Prospect as luminescence solar collector material

The present work describes the enhancement of green luminescence of Tb3+ ion in a newly synthesized composite material that contains Tb3+ and Yb3+ ions in Y2O3 nano-phosphor (TYY) coated with salicylic acid (SA) doped polyvinyl alcohol (PVA) polymer matrix (TYY: SA/PVA). XRD results reflect nearly 50 nm size of crystallite in TYY phosphor. On coating, the same with SA-doped PVA polymer visualizes the actual particulate size in microns due to aggregation of nano-crystallites of TYY and indicates the formation of organic/inorganic composite material. In down-conversion of UV radiation, both singlet and triplet states of excited state intra-molecular proton transfer species of SA in TYY: SA/PVA composite material transfer their UV (200 nm–370 nm) excitation energy through Fӧrster and Dexter mechanism to 5D4 state of Tb3+ ions, which enhances green luminescence of Tb3+ ions [5D4 →7F5] by nineteen-fold and decrease in the NIR luminescence intensity of Yb3+ ion [2F5/2 → 2F7/2] in TYY/SA/PVA as compared to the TYY sample indicates coating of SA/PVA polymer on the nano phosphor blocks the quantum cutting process from 4f75 d1 excited state of Tb3+ ions to 2F5/2 state of Yb3+ ions. In contrast, TYY: SA/PVA and TYY material exhibit intense green luminescent emission of Tb3+ ions by up-conversion of NIR radiation through a cooperative energy transfer between two Yb3+ ions [2F5/2 → 5D4 excitation]. A thin layer coating of composite phosphor material shows enhancement in the external quantum efficiency of the solar cell by increasing the efficiency of ∼3–5 % in the 400 nm–1000 nm range compared to the bare solar cell. I–V characteristics of the composite show that simultaneous excitation of this composite material with UV/Visible/NIR radiation increases the photon density in blue, green, and NIR regions for reabsorption by the photovoltaic cell. This preliminary study signifies the scope for developing brighter, high photon flux luminescent composite luminescent solar collecter material with low cost.