Graphene is a candidate material for next-generation high performance transparent conducting film (TCF) to replace indium tin oxide (ITO) materials. However, the sheet resistance of large area graphene obtained by the chemical vapor deposition (CVD) method is higher than other kinds of TCFs. The main strategies for improving the electrical conductivity of graphene films have been based on various doping treatments. AuCl3 is one of the most effective dopants. In this paper, we investigate the influence of AuCl3 doping on the conductive stability of CVD-grown graphene. Large area graphene film synthesized by CVD and transferred to glass substrates is taken as experimental sample. AuCl3 in nitromethane is used to dope the graphene films to improve the electrical conductivity. Another sample without doping is prepared for comparison. The resistances of graphene under periodic visible light irradiation with and without AuCl3 doping are measured. Results show that the resistances for all samples increase exponentially under lighting, while decrease slowly in an exponential form as well after the light is switched off. The relative resistance changes for undoped and doped samples are compared under 445nm light irradiation with 40mW/cm2, 60mW/cm2, 80mW/cm2, 100mW/cm2 in atmosphere and vacuum. The change rate and degree for doped graphene are greater than that of undoped graphene. It is evident from the experimental data that AuCl3 doping may induce conductive unstability for CVD-grown graphene on glass substrate.
The purpose of this study is to investigate the electrical properties of graphene transparent conductive film under visible light irradiation. Sample in the study is chemical vapor deposition (CVD) growth graphene on the surface of copper foils and then transferred to the SiO2 substrate. Three monochromatic visible lights with wavelength of 635nm, 520nm and 450nm representing red (R), green (G) and blue (B) lights are used as irradiation sources. Results show that the graphene resistances increase slowly under light irradiation with all the three different wavelengths, while decrease slowly after the light is switched off. Light irradiation with higher power density will induce larger relative resistance change. When graphene is irradiated at the same density, blue light irradiation may result in the largest resistance change.
This research examines the influence of lighting on the electrical properties of graphene on different substrates, including PET, glass and SiO2, which are the most widely used substrate materials representing the flexible and rigid applications. The graphene sheets were prepared by CVD and subsequently transferred to three substrates. The resistances of graphene under periodic visible light irradiation were measured inside a vacuum chamber. Results show that the resistances for graphene samples on all substrates increased slowly under lighting, while decreased slowly as well after the light was switched off. The change degree and speed were different for graphene on different substrates, which were influenced as well by the illumination time, environment atmosphere and irradiation power. Graphene on flexible PET substrate is more stable than that on other substrates.
In order to study the influence of road lighting standard on the photometric quantities and energy consumption, road lighting standards of CIE (International Commission on Illumination) and IESNA (Illuminating Engineering Society of North America) were compared in methodology, evaluation criteria and threshold. With the calculation of 20 typical assembly of roads and luminaries, it is found that the luminance is higher in IESNA than that in CIE. On the other hand, energy consumption is much less in IESNA than that in CIE under the same conditions.
If a surface light source is in far-field working condition, the error from using the inverse-square law about intensity and distance should be less than 1%. However, the results of where the far-field begin may be quite different with different error definition. In this paper, by comparing several formulas commonly used for error analysis, the root mean square (RMS) weighted by the sum of intensity at infinity is proposed as the preferred error formula for far-field distances calculation. The relative far-field distances (RFFDs) for LED arrays with different radiation pattern are calculated based on this error definition.
Organic light emitting diode (OLED) is a typical surface source with continuous luminous area. It is important to know its far-field condition since most of lighting designs are based on the far-field characteristics. In this paper, the relative far-field distances (RFFD) for OLEDs with round, rectangular, annular, hemispherical and semi-cylindrical shapes are calculated. The RFFDs for LED arrays with the same shapes are also given for comparison. Results show that the RFFDs for OLEDs are smaller than that of LED arrays with the same shapes and sizes for most situations.
The double-side patterned sapphire structure was proposed to improve the light extraction efficiency (LEE) of flip-chip
GaN-based light-emitting diodes (LEDs). The influences of sapphire substrate thickness, pattern shapes and sizes on
LEE were analyzed by Monte Carlo simulation method. Using silicon oxide as mask membrane, double-side patterned
sapphires were processed by the standard lithography and the reaction-ion-etching (RIE) technology. The LEDs with
patterned sapphire were packaged. The measured light outputs of LEDs verified our predicted effects.
Conventional road lighting luminaries are gradually upgraded by LED luminaries nowadays. It is an urgent problem to
design the light distribution of LED luminaries fixed at the former luminaries arrangement position, that are both energysaving
and capable of meeting the lighting requirements made by the International Commission on Illumination (CIE). In
this paper, a nonlinear optimization approach is proposed for light distribution design of LED road lighting luminaries, in
which the average road surface luminance, overall road surface luminance uniformity, longitudinal road surface
luminance uniformity, glare and surround ratio specified by CIE are set as constraint conditions to minimize the total
luminous flux. The nonlinear problem can be transformed to a linear problem by doing rational equivalent
transformation on constraint conditions. A polynomial of cosine function for the illumination distribution on the road is
used to make the problem solvable and construct smooth light distribution curves. Taking the C2 class road with five
different lighting classes M1 to M5 defined by CIE for example, the most energy-saving light distributions are obtained
with the above method. Compared with a sample luminary produced by linear optimization method, the LED luminary
with theoretically optimal lighting distribution in the paper can save 40% of the energy at the least.