LED Adaptive Deployment Optimization in Indoor VLC Networks

Driven by the continuous penetration of high data rate services and applications,a large amount of unregulated visible light spectrum is used for communication to fully meet the needs of 6th generation(6G)mobile technologies.Visible light communication(VLC)faces many challenges as a solution that complements existing radio frequency(RF)networks.This paper studies the optimal configuration of LEDs in indoor environments under the constraints of illumination and quality of experience(QoE).Based on the Voronoi tessellation(VT)and centroidal Voronoi tessellation(CVT)theory,combined with the Lloyd’s algorithm,we propose two approaches for optimizing LED deployments to meet the illumination and QoE requirements of all users.Focusing on(i)the minimization of the number of LEDs to be installed in order to meet illumination and average QoE constraints,and(ii)the maximization of the average QoE of users to be served with a fixed number of LEDs.Monte Carlo simulations are carried out for different user distribution compared with hexagonal,square and VT deployment.The simulation results illustrate that under the same conditions,the proposed deployment approach can provide less LEDs and achieve better QoE performance.

A dual-blue light-emitting diode based on strain-compensated InGaN-AlGaN/GaN quantum wells

A strain-compensated InGaN quantum well（QW） active region employing a tensile AlGaN barrier is analyzed.Its spectral stability and efficiency droop for a dual-blue light-emitting diode（LED） are improved compared with those of the conventional InGaN/GaN QW dual-blue LEDs based on a stacking structure of two In0.18Ga0.82N/GaN QWs and two In0.12Ga0.88N/GaN QWs on the same sapphire substrate.It is found that the optimal performance is achieved when the Al composition of the strain-compensated AlGaN layer is 0.12 in blue QW and 0.21 in blue-violet QW.The improvement performance can be attributed to the strain-compensated InGaN-AlGaN/GaN QW,which can provide a better carrier confinement and effectively reduce leakage current.

Bipolar Thermally Activated Delayed Fluorescence Emitter with Balanced Carrier Transport for High-Efficiency Nondoped Green Electroluminescent Devices

High-efficiency electroluminescent devices featuring simplified architecture have received considerable attention due to significant advantages in construction procedures and commercialized applications.However,there still remains a critical challenge with regard to the lack of organic semiconductors that simultaneously possess high luminescent efficiency and balanced carrier-transporting abilities.Herein,we design a thermally activated delayed fluorescence(TADF)emitter 4-(9,9-dimethyl-9,10-dihydroacridine)-4′-triphenylphosphineoxide-benzophenone(DMAC-BPTPO)by incorporating triphenylphosphine oxide into the donor–acceptor skeleton.The accessional electrontransporting moiety,rod-like dimer,and horizontally packing model synergistically enable DMAC-BP-TPO which possesses an excellent photoluminescence quantum yield of nearly 90%with a reverse intersystem crossing rate constant of 2.0×106 s−1,horizontal dipole ratio of 89%,and a balanced electron and hole mobilities with a small constrast ratio of 1.08.Eventually,simplified electroluminescent devices including organic lightemitting diodes(OLEDs)and organic light-emitting transistors(OLETs)incorporating DMAC-BP-TPO-based nondoped film are demonstrated due to their superior integrated optoelectronic properties along with preferable horizontal dipole orientation.A record-high external quantum efficiency value of 21.7%and 4.4%are finally achieved in the simplified nondoped OLED and OLET devices,which are among the highest values in the related research fields.This work provides a new avenue to develop a high-efficiency bipolar TADF emitter to advance the simplified electroluminescent devices.

Intrinsically Stretchable Electroluminescent Materials and Devices

Intrinsically stretchable electroluminescent(EL)devices have emerged as pivotal components with transformative potential in various domains,including wearable technology,medical devices,human-machine interfaces,and communications.This mini-review focuses on the recent progress in the development of intrinsically stretchable EL materials,highlighting milestones and breakthroughs in the field.The article discusses the basic principles,advantages,and disadvantages associated with various EL mechanisms and materials.Specific material design strategies,particularly focusing on light-emitting layers,are thoroughly examined,detailing their implementation in EL devices and the resultant EL performance.We also provide perspectives on the active challenges and future research needs for each type of EL material and devices for achieving stretchable designs,together with some insights into the future trajectory of stretchable EL technology.

Thermally activated delayed fluorescence materialsensitized helicene enantiomer-based OLEDs:a new strategy for improving the efficiency of circularly polarized electroluminescence

A new strategy of thermally activated delayed fluorescence(TADF)material-sensitized circularly polarized luminescence(CPL)has been proposed for improving the efficiencies of fluorescent circularly polarized organic lightemitting diodes(OLEDs)(CP-OLEDs).Consequently,a pair of helicene enantiomers,(P)-HAI and(M)-HAI,were synthesized.The helicene enantiomers with the rigid helicalπ-skeleton had highly thermal and enantiomeric stabilities,and they also showed excellent photophysical properties,especially,intense mirror-image CPL activities with large luminescence dissymmetry factor(|g_(lum)|)values of about 6×10^(-3).Notably,the CP-OLEDs with the helicene enantiomers as emitters and a TADF molecule as sensitizer not only displayed better performance of lower turn-on voltage(V_(T))of 2.6 V,four-fold maxmium-external quantum efficiency(EQE_(max))of 5.3%,and lower efficiencies roll-off of 1.9%at 1000 cd m^(-2),than those of the devices without TADF sensitizer,but also exhibited intense circularly polarized electroluminescence(CPEL)with the electroluminescence dissymmetry factor(g_(EL))values of-2.3×10^(-3)and+3.0×10^(-3).Meanwhile,this study also represents the first thermally activated sensitized fluorescent CP-OLEDs with markedly enhanced efficiencies and intense CPEL.

Inkjet printing for electroluminescent devices： emissive materials, film formation, and display prototypes

Inkjet priming （IJP） is a versatile technique for realizing high-accuracy patterns in a cost-effective manner. It is considered to be one of the most promising candidates to replace the expensive thermal evaporation technique, which is hindered by the difficulty of fabricating low-cost, large electroluminescent devices, such as organic light- emitting diodes （OLEDs） and quantum dot light-emitting diodes （QLEDs）. In this invited review, we first introduce the recent progress of some printable emissive materials, including polymers, small molecules, and inorganic colloidal quantum dot emitters in OLEDs and QLEDs. Subsequently, we focus on the key factors that influence film formation. By exploring stable ink formulation, selecting print parameters, and implementing droplet deposition control, a uniform film can be obtained, which in turn improves the device performance. Finally, a series of impressive inkjet-printed OLEDs and QLEDs prototype display panels are summarized, suggesting a promising future for IJP in the fabrication of large and high-resolution flat panel displays.

Simultaneous red-green-blue electroluminescent enhancement directed by surface plasmonic ＂far-field＂ of facile gold nanospheres

Based on the ＂far-field＂ effect of surface plasma resonance, simultaneous red-green-blue electroluminescence enhancement by facile synthesized gold nanospheres were realized in this work, which would be difficult and complex to attain using wavelength-selected localized surface plasma resonance. The plasmonic ＂far-field＂ effect can simultaneously enhance the whole emission region in the white light range, because the enhancing regions from blue to red emission are largely overlapped. By doping gold nanospheres embedded in a poly（3,4-ethylene dioxythiophene）：polystyrene sulfonic acid （PEDOT：PSS） layer, yield enhancement is achieved in more than 95% devices with the best enhancing ratio of 60% and the commission International de UEclairage （CIE） coordinate is stable at approximately （0.33, 0.36）. The plasmonic ＂far-field＂ effect requires an ultra-low working concentration of Au NPs in picomolar magnitude, and shows little negative effect on the electronic process and light scattering, which has big potential in realizing highly efficient white organic light emitting diodes.

Organic composite materials:Understanding and manipulating excited states toward higher light-emitting performance

Organic composite materials have been attracting extensive research interest for light-emitting applications.A wide variety of luminescent organic composite materials have been synthesized,which are of great significance for both the investigation of basic photophysics and the realization of high-performance photonic devices.Function-oriented syntheses of luminescent organic composite materials rely on the understanding and manipulating of molecular excited states.In this review,we focus on the discussion about the structure design and dynamics modulation of the electronic excited states in the organic composite materials.The excited-state structures and dynamics involve singlet/triplet levels,vibronic transition,charge transfer,and energy transfer,and so on,while the light-emitting behaviors include fluorescence,phosphorescence,persistent luminescence,electroluminescence,and lasing.We aim to give insight into the relationship between light-emitting properties and excited states of organic composite materials,which is beneficial for reaching higher tiers of design and applications of luminescent organic composite materials.

Versatile Aggregation-Enhanced Delayed Fluorescence Luminogens Functioning as Emitters and Hosts for High-Performance Organic Light-Emitting Diodes

Severe efficiency instability is still a huge challenge for most organic light-emitting diodes(OLEDs)based on thermally activated delayed fluorescence(TADF)molecules,frustrating their industrial application.To address this issue,herein we report two robust luminogens,3,6-bis(9,9-dimethylacridin-10-yl)-xanthen9-one(BDMAC-XT)and 3,6-bis(9,9-diphenylacridin-10-yl)-xanthen-9-one(BDPAC-XT),comprised of electron-accepting 3,6-dibromoxanthen-9-one and electron-donating 9,9-dimethyl-9,10-dihydroacridine and 9,9-diphenyl-9,10-dihydroacridine.

Simple dynamic energy core equivalent rays method to design freeform surface for extended source

A simple method is proposed to design free- form surface for Lambertian extended source. In this method, it can take advantage of the designing method for point source via substituting each incident ray with a dynamically calculated equivalent ray. For each facet on the freeform surface, the equivalent ray emits from the energy weighted average-emitting-position for the corre- sponding incident beam, and redirects into the direction which is determined by a source-to-target mapping. The results of the designing examples show that the light distributions＇ uniformities can be improved by this method, e.g., even the improvement of 59% can be achieved.