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GaN-based light-emitting diodes suffer from high-current loss mechanisms that lead to a significant decrease in internal quantum efficiency at high drive currents. This phenomenon, known as "efficiency droop," is a major problem for solid-state lighting applications, in which light-emitting diodes are driven at high currents to deliver large optical powers. Although substantial effort has been invested to uncover the physical origin and mitigate the effects of efficiency droop, there is still a lack of consensus on the dominant mechanism responsible. In this article, we review several mechanisms that have been proposed as explanations of efficiency droop, including junction heating, carrier delocalization, Auger recombination, and electron leakage from the active region. In addition, device structures intended to mitigate the droop-causing mechanism – (i) thick quantum wellsl, (ii) enhanced hole-injection efficiency structures, and (iii) polarization-matched active region – are discussed.

In this paper, extraction efficiency in simplified and layered light-emitting diodes (LEDs) of GaN photonic crystal with periodic air holes is studied by three-dimensional finite-difference time-domain method. Photonic band structures of the photonic crystal are obtained by plane-wave expansion method. The results about simplified GaN-LED show that extraction efficiency is very sensitive to the structure parameters tuning, and increases considerably inside the transverse-electric-like gap region. A maximum extraction efficiency above 90% can be achieved. The effects of the PC thickness and air-hole radius on relative extraction efficiency of layered GaN-LED are analyzed. They show optimal values to obtain high relative extraction efficiency.

A series of dendritic 2,3,4,5-tetraphenylsiloles (1–8) are prepared. Polymerizations of 4-8 are effected by transition-metal catalysts, giving linear (9-12) and hyperbranched polymers (14) in high yields. Whereas the silole polymers are practically nonluminescent when molecularly dissolved, they become emissive when aggregated in poor solvents or cooled to low temperatures. The light-emitting diodes using linear poly(silolylacetylene)s as active layers emit blue and green lights with current efficiency up to 1.45 cd/A. The hyperbranched poly(silolenearylene)s are nonlinear optically active and strongly attenuate the optical power of intense laser pulses, whose optical limiting performances are superior to that of C₆₀, a well-known optical limiter.

Electroluminescence cooling of a heated infrared-emitting diode has been claimed [P. Santhanam, D. J. Gray, Jr. and R. J. Ram, Thermoelectrically pumped light-emitting diodes operating above unity efficiency, Phys. Rev. Lett.108 (2012) 097403]. After analyzing the operating characteristics of this diode, it is evident that electroluminescence cooling was not demonstrated.

Gold nanoparticles (Au NPs) have promising applications in the fields of drug delivery and photothermal therapy. 5-hydroxydecanoate (5-HD) is a kind of highly selective mitochondrial ATP sensitive potassium (mitoKATP) channel blocker. In this research, firstly, 5-HD was studied whether it could induce human lung adenocarcinomas (A549) cells apoptosis; secondly, PEGylated gold nanoparticles loaded with 5-HD (Au NPs-PEG-5-HD) were prepared to develop a new chemotherapy and photothermal therapy in one system under the irradiation of green light-emitting diode (LED). Subsequently, in vitro cytotoxicity test was analyzed by cell counting kit-8 (CCK-8), the change of mitochondrial membrane potential (Δψm) was determined by immunofluorescence microscopy with R-123 fluorescence, and cell apoptosis and necrosis rate were detected by flow cytometry. The results of CCK8 revealed that the inhibition rates of A549 cells were all greatly increased when cells were treated with free 5-HD, free 5-HD +LED irradiation, Au NPs-PEG-5-HD and Au NPs-PEG-5-HD+LED irradiation, and Au NPs-PEG-5-HD had enhanced cell-killing effect compared with 5-HD, furthermore, the Au NPs-PEG-5-HD and LED irradiation played a very great synergy effect. The immunofluorescence microscopy data also exhibited a reduction of Δψm correspondingly. Flow cytometric analysis showed that the apoptosis rate of cells that were incubated with free 5-HD, 5-HD+LED irradiation, Au NPs-PEG-5-HD or Au NPs–PEG–5-HD+LED irradiation significantly increased to about 9.2%, 10.7%, 18.3% or 12.4% and the percentage of necrosis cells increased to around 8.8%, 9.7%, 48.0% or 69.8%, respectively. In a word, all the results indicated that the 5-HD had shown the ability to induce A549 cells apoptosis as a chemotherapy agent, and its ability would be improved when 5-HD is loaded on PEGylated Au NPs, as well as Au NPs-PEG-5-HD exhibited significantly enhanced photothermal effects for treatment of lung adenocarcinomas.

Photoacoustic imaging, an emerging biomedical imaging modality, holds great promise for preclinical and clinical researches. It combines the high optical contrast and high ultrasound resolution by converting laser excitation into ultrasonic emission. In order to generate photoacoustic signal efficiently, bulky Q-switched solid-state laser systems are most commonly used as excitation sources and hence limit its commercialization. As an alternative, the miniaturized semiconductor laser system has the advantages of being inexpensive, compact, and robust, which makes a significant effect on production-forming design. It is also desirable to obtain a wavelength in a wide range from visible to near-infrared spectrum for multispectral applications. Focussing on practical aspect, this paper reviews the state-of-the-art developments of low-cost photoacoustic system with laser diode and light-emitting diode excitation source and highlights a few representative installations in the past decade.

This paper reports a hybrid optrode combining light-emitting diodes (LEDs) and microelectrodes on a polycrystalline diamond (PCD) substrate, for optogenetic stimulation and electrical recording of neural activity. Thermally conductive PCD can dissipate the Joule heat to surrounding areas, and thus reduce the risk of thermal damage to nerve tissues. During repetitive optical stimulation, the maximum temperature rise of the PCD optrode was less 1.3°C. The functionality of the PCD probe was tested in vivo where light-evoked action potentials were successfully detected.