Advancement in materials for energy-saving lighting devices

This review provides a comprehensive account of energy efficient lighting devices, their working principles and the advancement of these materials as an underpinning to the development of technology. Particular attention has been given to solid state lighting devices and their applications since they have attracted the most interest and are the most promising. Solid state lighting devices including white light emitting diodes （LEDs）, organic LEDs （OLEDs）, quantum-dot LEDs （QLEDs） and carbon-dot LEDs （CLEDs） are promising energy efficient lighting sources for displays and general lighting. However there is no universal solution that will give better performance and efficiency for all types of applications. LEDs are replacing traditional lamp,; for both general lighting and display applications, whereas OLEDs are finding their own special application,; in various areas. QLEDs and CLEDs have advantages such as high quantum yields, narrow emission spectra, tunable emission spectra and good stability over OLEDs, so applications for these devices are being extended to new types of lighting sources. There is a great dean of research on these materials and their processing technologies and the commercial viability of these technologies appears strong.

Polymer light-emitting devices using poly(ethylene oxide) as an electron injecting layer

The performance of polymer light emitting devices(PLEDs)based on polyvinyl carbazole(PVK)is improved by introducing a nanoscale interfacial thin layer,made of poly(ethylene oxide)(PEO),between the calcium cathode and the PVK emissive layer.It is believed that the PEO layer plays a key role in enhancing the device performance.In comparison to the device with Ca/Al as the cathode,the performance of the PLED with PEO/Ca/Al cathode,including the driving voltage,luminance efficiency is significantly improved.These improvements are attributed to the introduction of a thin layer of PEO that can lower the interfacial barrier and facilitate electron injection.

STUDY OF DEGRADATION MECHANISM AND PACKAGING OF ORGANIC LIGHT EMITTING DEVICES

Organic Light Emitting Devices (OLED) have attracted much attention recently, for their applications in futureFlat Panel Displays and lighting products. However, their fast degradation remained a major obstacle to theircommercialization. Here we present a brief summary of our studies on both extrinsic and intrinsic causes for the fastdegradation of OLEDs. In particular, we focus on the origin of the dark spots by 'rebuilding' cathodes, which confirms thatthe growth of dark spots occurs primarily due to cathode delamination. In the meantime, we recapture the findings from thesearch for suitable OLED packaging materials, in particular polymer composites, which provide both heat dissipation andmoisture resistance, in addition to electrical insulation.

Improved device reliability in organic light emitting devices by controlling the etching of indium zinc oxide anode

A controllable etching process for indium zinc oxide （IZO） films was developed by using a weak etchant of oxalic acid with a slow etching ratio. With controllable etching time and temperature, a patterned IZO electrode with smoothed surface morphology and slope edge was achieved. For the practical application in organic light emitting devices （OLEDs）, a sup- pression of the leak current in the current-voltage characteristics of OLEDs was observed. It resulted in a 1.6 times longer half lifetime in the IZO-based OLEDs compared to that using an indium tin oxide （ITO） anode etched by a conventional strong etchant of aqua regia.

Do UV LED Devices Immolate SARS-CoV2?

Some manufactures made UVC LED Strip as disinfection tool against SARS-CoV2. Therefore, three types of commercially UVC lights were used to evaluate their efficiency to warp bacteria and viruses. We tested three commercially available UV lights devices. They were put at 4 to 5 cm to spiked sterile Petri dishes (samples) for 10, 20, 30, and 60 seconds and compared it to control (without UV light exposure). Also, the same three UV LED devices were used on Positive SARS-CoV2 swab samples (used for the Petri dishes). Serial dilutions of the cultured microbes were used for the experiment as follows: 1/10 (high concertation), 1/100, 1/1000, 1/10,000, 1/100,000 (low concertation). All three UV LED devices (DA, DB, DC) were found to have no effects on the pathogens (Bacteria or SARS-CoV2), even to the lowest Bacteria Concentration (1/100,000), when pathogens were exposed to UV radiation for 10, 20, 30, and 60 sec at distance a 4 to 5 cm. One of the manufacturers of these UVC lights (DB) claims that the device is very effective in killing Bacteria and Virus immediately at a 99.93% killing rate (in 20 sec.). This observation was not noticed. False claims may lead to severe spread of SARS-CoV2 as customers may think that the DB was disinfecting, after short exposure, while truly having no effect.

Treatment of Peripheral Neuropathy: Combination Therapy Using LED Light, Extracorporeal Shockwave Therapy, Platelet Rich Plasma, and an Oral Dietary Supplement

Objectives: Peripheral neuropathy (PN) is a significant contributor to disability in the elderly. It is also one of the most prevalent complications of type 2 diabetes, prediabetes and metabolic syndrome. PN is commonly associated with pain, numbness, tingling, burning, and cramping in the feet and legs. Current treatment options are limited to controlling pain, seizures and use of antidepressant medications. These treatments have undesirable side effects and don’t stop PN progression. Here we utilized a combination of individual-specific modalities to improve local circulation and relieve PN symptoms. Methods: We conducted an open-label, multicenter pilot trial with 34 subjects (19 males and 15 females ranging from 40 - 85 years of age). All of the participants were diagnosed with peripheral neuropathy and had bilateral symptoms in their feet, and many reported the same symptoms (pain, numbness, tingling, burning, and cramping) in their lower legs. The duration of symptoms ranged from four months to over six years. On Day 0, subjects were given a 90-day supply of the oral supplement with dosing instructions and a LED light therapy device. They also received three platelet-rich plasma (PRP) injections in their lower extremities. Subjects also received an extracorporeal shockwave therapy (ESWT) treatment for each foot and subsequently twice per week for the first six weeks, then once weekly for the duration of the study. Subjects filled out the Brief Pain Index (BPI) at weekly intervals. On Day 90, subjects completed the Patient Global Impression of Change (PGIC) survey. Results: There were significant responses to pain, as evidenced by BPI scores at weeks 8, 9, 10 and 11 (p = 0.02, 0.01, 0.02, and 0.003, respectively). Analysis of the final day PGIC survey showed a favorable outcome for 73% of participants (p = 0.003), with the majority reporting Very Much Improved. Conclusions: By utilizing a multi-modality treatment protocol that includes PRP, LED light therapy, ESWT and an oral dietary supplement, we observed significant reductions in BPI scores. Quality of life and their overall impression of change (PGIC) were significantly improved, and there were no significant side effects.

Multifunctional silicon-based light emitting device in standard complementary metal oxide semiconductor technology

A three-terminal silicon-based light emitting device is proposed and fabricated in standard 0.35 μm complementary metal-oxide-semiconductor technology. This device is capable of versatile working modes： it can emit visible to near infra-red （NIR） light （the spectrum ranges from 500 nm to 1000 nm） in reverse bias avalanche breakdown mode with working voltage between 8.35 V-12 V and emit NIR light （the spectrum ranges from 900 nm to 1300 nm） in the forward injection mode with working voltage below 2 V. An apparent modulation effect on the light intensity from the polysilicon gate is observed in the forward injection mode. Furthermore, when the gate oxide is broken down, NIR light is emitted from the polysilicon/oxide/silicon structure. Optoelectronic characteristics of the device working in different modes are measured and compared. The mechanisms behind these different emissions are explored.

Significant Lifetime Enhancement in QLEDs by Reducing Interfacial Charge Accumulation via Fluorine Incorporation in the ZnO Electron Transport Layer

ZnO nanoparticles are widely used for the electron transport layers(ETLs)of quantum dots light emitting devices(QLEDs).In this work we show that incorporating fluorine(F)into the ZnO ETL results in significant enhancement in device electroluminescence stability,leading to LT50 at 100 cd m^(−2) of 2,370,000 h in red QLED,47X longer than the control devices.X-ray photo-electron spectroscopy,time-of-flight secondary ion mass spectroscopy,photoluminescence and electrical measurements show that the F passivates oxygen vacancies and reduces electron traps in ZnO.Transient photoluminescence versus bias measurements and capacitance-voltage-luminance measurements reveal that the CF4 plasma-treated ETLs lead to increased electron concentration in the QD and the QD/hole transport layer interface,subsequently decreasing hole accumulation,and hence the higher stability.The findings provide new insights into the critical roles that optimizing charge distribution across the layers play in influencing stability and present a novel and simple approach for extending QLED lifetimes.

Superpixel-Based Complex Field Modulation Using a Digital Micromirror Device for Focusing Light through Scattering Media

We present a digital micromirror device（DMD） based superpixel method for focusing light through scattering media by modulating the complex field of incident light. Firstly, we numerically and experimentally investigate focusing light through a scattering sample using the superpixel methods with different target complex fields.Then, single-point and multiple-point focusing experiments are performed using this superpixel-based complex modulation method. In our experiment, up to 71.5% relative enhancement is realized. The use of the DMDbased superpixel method for the control of the complex field of incident light opens an avenue to improve the enhancement of focusing light through scattering media.

Fabrication and temperature-dependent photoluminescence spectra of Zn–Cu–In–S quaternary nanocrystals

A series of Zn-Cu-In-S nanocrystals （ZCIS NCs） are prepared and the optical properties of the ZCIS NCs are tuned by adjusting the reaction time. It is interesting to observe that the temperature-dependent photoluminescence （PL） spectra of the ZCIS NCs show a redshift with decreasing intensity at low temperature （50-280 K） and a blueshift at high temperature （318--403 K）. The blueshift can be explained by the thermally active phonon-assisted tunneling from the excited states of the low-energy emission band to the excited states of the high-energy emission band.

Organic Light Emitting Diodes with p-Si Anodes and Semitransparent Ce/Au Cathodes

The Ce （x nm）/Au （15 nm） stacked layers were used as semitransparent cathodes in the top-emission organic light emitting devices （TOLEDs） fabricated on a p-type silicon anodes and substrate,where x varies from 4 to 16.The consequence of the Ce layer thickness on transmittance and the device performance were studied when the organic layers NPB （60 nm）/ALQ （60 nm） were kept unchanged,where NPB was N,N＇-bis-（1-naphthl）-diphenyl-1,1＇-biphenyl-4,4＇-diamine,and AlQ is tris-（8-hydroxyquinoline） aluminum.The cathode of Ce （11 nm）/Au （15 nm） has a transparency of 46%,and the TOLED with it achieves the highest luminescence efficiencies：a current efficiency of 0.91 cd/A at 13.7 V and a peak power efficiency of 0.28 lm/W at 9 V.The turn-on voltage is 3.0 V.The Ce/Au cathode is both chemically and electrically stable.

Light energy conversion device for photocatalyst 2.0%WO_3-TiO_2 with oxygen vacancies for water splitting

Using carbon felt, polytetrafluoroethylene latex and powder catalyst to assembly a light energy conversion device, the photocatalytic activity of catalyst 2.0%WO3-TiO2 （2%WO3 compounding TiO2） with oxygen vacancies was studied through the water splitting for O2 evolution, using a high pressure mercury lamp as the light source and Fe^3＋ as the electron acceptor in two different devices： an ordinary photolysis device with catalyst powder suspending through a magnetic stirrer and a self-assembly light energy conversion device. The results show that after 12 h irradiation, the photocatalytic activity of 2.0%WO3-TiO2 with oxygen vacancies in the self-assembly light energy conversion device is higher than that of the ordinary photolysis device, and the amount of oxygen evolution is about 12 and 9 mmol/L respectively in these two devices. After 12 h, the rates of 02 evolution are slow in each device and the photocatalyst almost loses the photoactivity in the ordinary photolysis device. So, compared with the ordinary photocatalytic device, the rate of oxygen evolution and the life time of the catalyst are improved in the self-assembly light energy conversion device.

PROBING PLASMA SPECIES IN A TM_(010) CAVITY

ith the aid of a fibre optical device, the profile of plasma parameters, such as plasma length and noise power spectrum, in a normally enclosed TM 010 cavity was probed. Experimental results show that the physical length of a plasma is linearly related to the microwave power applied and that the profile of noise power spectra varies significantly along the length of a plasma.

Multicolor emission from lanthanide ions doped lead-free Cs_(3)Sb_(2)Cl_(9) perovskite nanocrystals

The toxicity of lead ions has become the severe challenge for the all-inorganic lead halide p erovskite materials,although some works have rep orted the lead-free perovskite nanocrystals(NCs),the photoluminescence quantum yield(PLQY)of these materials is still unsatisfactory.Meanwhile,because the halogen ions can be easily exchanged,the controllable multicolor emission in perovskite NCs is difficult to realize in current reports.In this work,we introduced lanthanide ions into lead-free Cs_(3)Sb_(2)Cl_(9) perovskite NCs.Benefitting from the energy transfer between Cs_(3)Sb_(2)Cl_(9) perovskite NC host and lanthanide ions,the multicolor emission was realized.Based on controlling the doping concentration of Tb^(3+)and Eu^(3+)ions,the white light emission under UV excitation would be turned easily in the Tb^(3+)/Eu^(3+)codoped NCs.In addition,efficient energy transfer from perovskite NCs to Tb^(3+)or Eu^(3+)ions is beneficial to improving the optical properties of lead-free perovskite NCs,resulting in maximum PLQYs of red,green and white light emission of 22.6%,19.7%and 28.5%,respectively.Finally,a white light emitting device(WLED)was fabricated with a power efficiency of 18.5 lm/W,which presents the Commission Internationale de l'Eclairage(CIE)of(0.33,0.35).

A systematic study on efficiency enhancements in phosphorescent green, red and blue microcavity organic light emitting devices

A systematic study has been conducted on microcavity organic light emitting diodes(OLEDs)based on green,red and blue phosphorescent emitters to elucidate the microcavity effects for different color emitters.We found that the luminance output is determined by the reflectivity of the semitransparent electrode and the photopic response of the green,red and blue emitters.While the luminance enhancements of blue and red phosphorescent microcavity devices are small,a current efficiency as high as 224 cd A21 is obtained in the green phosphorescent microcavity OLEDs.

Host molecule enhanced aggregation induced emission of chiral silver nanoclusters for achieving highly efficient circularly polarized electroluminescence

Chiral metal nanoclusters(MNCs)are competitive candidates for fabricating circularly polarized light-emitting diodes(CPLEDs),but the device performance is greatly limited by the poor emission of MNCs in solid thin films.Herein,host molecule enhanced aggregation induced emission(AIE)of MNCs is demonstrated for fabricating highly efficient CPLEDs.Namely,on the basis of the AIE effect of atomically precise enantiomeric(R/S)-4-phenylthiazolidine-2-thione capped silver(R/S-Ag_(6)(PTLT)_(6))NCs in solid thin films,1,3-bis(carbazol-9-yl)benzene(mCP)is introduced as a host molecule to control the orientation and packing arrangements of R/S-Ag_(6)(PTLT)_(6) NCs throughπ–πinteractions with the R/S-Ag_(6)(PTLT)_(6) NCs and further enhance the AIE.The as-fabricated Ag_(6)(PTLT)_(6) NC/mCP hybrid solid thin film shows a high photoluminescence quantum yield of 71.0%close to that of Ag_(6)(PTLT)_(6) NC single crystal.As the hybrid films are employed as the active emission layers of CPLEDs,mCP also suppresses the triplettriplet annihilation and balances the charge transport.Thus,the CPLEDs exhibit a maximum brightness of 3,906 cd/m^(2),peak external quantum efficiency of 10.0%,electroluminescence dissymmetry factors of−5.3×10^(−3)and 4.7×10^(−3).

Discretely-supported nanoimprint lithography for patterning the high-spatial-frequency stepped surface

Non-planar morphology is a common feature of devices applied in various physical fields,such as light or fluid,which pose a great challenge for surface nano-patterning to improve their performance.The present study proposes a discretely-supported nanoimprint.lithography(NIL)technique to fabricate nanostructures on the extremely non-planar surface,namely high-spatial-frequency stepped surface.The designed discretely imprinting template implanted a discretely-supported intermediate buffer layer made of sparse pillars arrays.This allowed the simultaneous generation of air-cushion-like buffer and reliable support to the thin structured layer in the template.The resulting low bending stiffness and distributed concentrated load of the template jointly overcome the contact difficulty with a stepped surface,and enable the template to encase the stepped protrusion as tight as possible.Based on the proposed discretely-supported NIL,nanostructures were fabricated on the luminous interface of light emitting diodes chips that covered with micrometer step electrodes pad.About 96%of the utilized indium tin oxide transparent current spreading layer surface on top of the light emitting diode(LED)chips was coated with nanoholes array,with an increase by more than 40%in the optical output power.The excellent ability of nanopatterning a non-planar substrate could potentially lead innovate design and development of high performance device based on discretely-supported NIL.

Two-dimensional materials for light emitting applications:Achievement,challenge and future perspectives

The two-dimensional(2D)materials have been widely developed recently in material characteristics with advanced optical and electrical properties,and they have been extensively studied as candidates for the next generation of optoelectronic devices.This review will mainly focus on the preparation methods and the light emitting applications of 2D transition metal dichalcogenides(TMDs),2D black phosphorene(BP)and 2D perovskites.The review will first introduce the preparation methods for TMDs and BP.Due to the variations of band structure,exciton binding energies and light-matter interaction in TMDs and BP,the different light emitting devices(LEDs)designs based on TMDs and BP will be discussed and summarized.Then the review will turn the focus to 2D perovskites,starting with a description of the preparation methods for the different structural perovskites.In order to review and summarize the achievements of 2D perovskites-based LEDs,the high efficiency perovskites LEDs are discussed.Finally,the review will present challenges,opportunities,and outlook for the future development of 2D materials-based light emitting applications.

New Device Sheds Light on Mechanism,Efficacy of Arthritis Treatment

The debate over how one of the most popular osteoarthritis treatments should be federally regulated could change,thanks to a Cornell University study and a new device that provides a better understanding of the science behind hyaluronic acid(HA)injections.