Electroluminescent Sources Research Articles

Shaping the spontaneous emission of extended incoherent sources into composite radial vector beams

It is well known that concentric diffraction gratings are capable of beaming the spontaneous emission of large extended incoherent light sources (e.g., hot radiating surfaces and luminescent materials). Here, we reveal additional properties of such beams using layers of colloidal PbS nanocrystals coated onto metallic spiraling gratings as an example. We observe and explain the formation of multiple beams with a simple model when the spirals are deformed. We also point out an aspect of the light emission that does not seem to have been discussed so far—namely, that the polarization of the directional beams has a radial distribution. These findings are not restricted to our experimental configuration, suggesting a simple way to build incandescent and electroluminescent sources with non-trivial polarization states. The price to pay is an isotropic emission background due to the composite nature of the beams, which result from the incoherent superposition of a continuum of diffracted plasmons everywhere above the surface.

General relation between spatial coherence and absorption

Despite the fact that incandescent sources are usually spatially incoherent, it has been known for some time that a proper design of a thermal source can modify its spatial coherence. A natural question is whether it is possible to extend this analysis to electroluminescence and photoluminescence. A theoretical framework is needed to explore these properties. In this paper, we extend a general coherence-absorption relation valid at equilibrium to two non-equilibrium cases: luminescent bodies and anisothermal bodies. We then use this relation to analyse the differences between the isothermal and anisothermal cases and to study the near-field emission of an electroluminescent source.

Electroluminescent layers based on ZnS:Cu deposited into matrices of porous anodic Al2O3

It is suggested to use a new nanocomposite material—nanostructures of copper-doped zinc sulfide in a matrix of porous aluminum oxide—as a light-emitting layer of electroluminescent sources of light. The material was deposited by thermal evaporation in a vacuum. The microstructure of the layers, impurity distribution in the electroluminescent-phosphor layer, and electroluminescence spectra at various copper concentrations in ZnS:Cu were studied.

Single InGaN nanodisk light emitting diodes as full-color subwavelength light sources

Subwavelength electroluminescent sources with spatial, spectral, and polarization controlling capabilities are critical elements for optical imaging and lithography beyond the diffraction limit. Here, we show that the electroluminescence from single, strain-free InGaN nanodisks embedded in self-assembled GaN p-n nanorods can span the entire visible spectrum with a large linear polarization ratio (∼0.85). Furthermore, this unique nanodisk-in-nanorod geometry enables the realization of the ultrasmall footprint light-emitting diodes (LEDs) to be used as subwavelength light sources. Using these nano-LEDs, we are able to demonstrate near-field, subwavelength photolithography by controlling the exposure time and light intensity from single InGaN nanodisks at chosen wavelengths.

Reliability of High-Power Light Emitting Diode Attached With Different Thermal Interface Materials

As a solid electroluminescent source, white light emitting diode (LED) has entered a practical stage and become an alternative to replace incandescent and fluorescent light sources. However, due to the increasing integration and miniaturization of LED chips, heat flux inside the chip is also increasing, which puts the packaging into the position to meet higher requirements of heat dissipation. In this study, a new interconnection material—nanosilver paste is used for the LED chip packaging to pursue a better optical performance, since high thermal conductivity of this material can help improve the efficiency of heat dissipation for the LED chip. The bonding ability of this new die-attach material is evaluated by their bonding strength. Moreover, high-power LED modules connected with nanosilver paste, Sn3Ag0.5Cu solder, and silver epoxy are aged under hygrothermal aging and temperature cycling tests. The performances of these LED modules are tested at different aging time. The results show that LED modules sintered with nanosilver paste have the best performance and stability.

Electroluminescent sources of light based on ZnSe: Mn single crystals with optimum brightness

Electroluminescent sources of light based on plastically deformed ZnSe: Mn single crystals are studied. It is shown that the emissivity of the electroluminescent sources depends on the manganese concentration and the part of a ZnSe: Mn boule from which a plane-parallel wafer is cut.

Thin-film electroluminescent devices: Influence of Mn-doping method and degradation phenomena

Comparative experiments on ac thin-film electroluminescent (ACTFEL) emitters show the influence of the electroluminescent source material preparation on the L(V) characteristic. The influence on the polycrystalline structure has been investigated by Scanning Transmission Electron Microscopy (STEM). Different types of degradation occurring during sustained operation of the devices are reported and solutions proposed.

Fiber optic lever displacement transducer

Intrinsic performance limits of noncontacting fiber lever displacement measuring systems are quantitatively described. Generalized relationships linking displacement detection limit, frequency response, dynamic range, linearity, and working distance to fiber diameter, illumination irradiance and coupling angle, photodetector characteristics, and reflection and transmission losses were obtained by analysis and confirmed by measurement. Both procedures showed performance limits to be functions of the square root of the flux density coupled into the target-illuminating fiber(s) by the electroluminescent source. Displacement detection and bandwidth limits achievable with tungsten or LED sources were in the 2 x 10(-11) to 2 x 10(-12) [equation] and MHz, range respectively. A basis for optimizing levers for different applications and determination of intrinsic performance limits is provided.

The relationship between the intensity of repetitive photic stimulation and the cerebral response

Sixteen healthy subjects were subjected to flicker at four intensities (modulation depths) of square wave stimuli from an electro-luminescent source. Each subject was stimulated at eight flash rates ranging from 6 to 30 c/sec at each ot the four intensities and the whole procedure was performed twice in one session. Recordings were taken from a single pair of electrodes on the occiput and vertex. The cerebral rhythms were analysed by means of a frequency analyser. The principal results were as follows: 1. (1) During stimulation at the lowest rate (6 c/sec) and at the higher rates (16–30 c/sec) the fundamental response increased with each increase in intensity. The relationship was approximately linear when the log response was plotted against intensity on a linear scale. 2. (2) During stimulation at the intermediate rates (8–12 c/sec) the fundamental response increased with the intensity only up to a certain point. A further increase in intensity resulted in a decrease in response. 3. (3) During stimulation at 8–12 c/sec the second harmonic response showed a similar trend with intensity to that of the fundamental response. It was concluded that the inverted U-shaped relationship between fundamental response and intensity at 8–12 c/sec could not be attributed to blocking of the alpha rhythm at the higher intensities or to frequency doubling. The relationship between the pattern of response to stimulation and the frequency spectrum of the spontaneous rhythms was examined between subjects. It was found that: 1. (1) The more prominent a subject's alpha rhythm by comparison with those of other subjects, the greater tended to be the fundamental responses at 8–12 c/sec. The correlation increased with each increase in intensity, which suggested that it was not solely attributable to persistence of the alpha rhythm during stimulation. 2. (2) The more prominent the alpha rhythm, the smaller tended to be the responses at 20 and 24 c/sec. The relationship became more negative with each increase in intensity. 3. (3) The more prominent the faster rhythms, the greater tended to be the responses at 20 and 24 c/sec. This relationship became less positive with increasing intensity. These findings are in general agreement with previous reports.