Characterization of Nepali solid-state lamps

Solid-state lighting technology based on injection electroluminescence devices, light-emitting diodes (LEDs), already found numerous applications in traffic lights, automotive signage, full-colour video displays, liquid crystal display backlighting, optical measurements, phototherapy, and other niche applications. The development of white LEDs based on partial or complete conversion of short-wavelength radiation in phosphors and phosphor blends and recent progress in compound semiconductor and phosphor materials quality and photonic design of the chips resulted in that LEDs are also considered as promising candidates in general lighting. General lighting based on solid-state lamps has a high potential in energy saving, offers vast environmental benefits, and features unsurpassed longevity, reduced maintenance, and functionality. In industrialized countries where electrical lighting is very common, solid-state lighting meets high competition from conventional sources of light, such as incandescent, fluorescent, high-pressure sodium, and metal-halide lamps. Meanwhile in developing countries, especially in rural area, LEDs encroach on the lighting market occupied by fuel-based sources, such as firewood and kerosene lamps. Owing to high efficiency, compatibility with off-network and rechargeable-battery-based d. c. sources of electrical power, such as photovoltaic, hydro, wind, and pedal generators, LEDs are the most appropriate sources for such substitution with huge benefits in energy consumption, cost, as well as in resolving education and health issues [4,5]. In particular, fuel-based sources have luminous efficiency below 0.1 lm/W comparing to 15-80 1m/W of present commercial LEDs with a potential of attaining 200-1m/W efficiency in the nearest future. To this end, penetration of solid-state lighting technology to general lighting might be even faster in developing countries than in industrialized ones, especially with international support taken into account. Solid-state lamps are a novel source for general lighting with no well-established standards developed so far. However because of cost pressure, fabrication of solid-sate lamps for developing countries is drawn to local manufacturing facilities, which lack instrumental characterization. Meanwhile the conditions of exploitation of lighting devices in developing countries are much harsher than in industrialized ones and involve wide ranges of temperature and humidity, variation in driving voltage, and smoking from organic-fuel based stoves. This draws a need in international cooperation on characterization of solid-state lamps manufactured in developing countries. The present work aimed at the temperature, directional, and chromatic characterization of solid-state lamps manufactured for Rural Integrated Development Services-Nepal (RIDS-Nepal) village illumination programs

Study of Optical and Photoelectrical Properties of 3c-Sic Single Crystals and Heterostructures

Cubic silicon carbide (3C-SiC) with the energy band gap 2.36 eV (T=300K) possess relatively high electron mobility and appears as promising material for applications in high power and temperature electronics and devices for harsh environment. We review optical techniques able to investigate the optical and photoelectrical properties of SiC at high injection levels. The excess carriers were injected by a short laser pulse and monitored by timeresolved free-carrier absorption (FCA) and light-induced transient grating (LITG) techniques. We also investigated spectra of room-temperature photoluminecense (RTPL), as a complementary technique to reveal defect-related properties. We note that latter technique up to now was mainly used to study low-temperature photoluminescence spectra of SiC

Carrier Lifetimes and Influence of In-Grown Defects in N-B Co-Doped 6H-SiC

The thick N-B co-doped epilayers were grown by the fast sublimation growth method and the depth-resolved carrier lifetimes have been investigated by means of the free-carrier absorption (FCA) decay under perpendicular probe-pump measurement geometry. In some samples, we optically reveal in-grown carbon inclusions and polycrystalline defects of substantial concentration and show that these defects slow down excess carrier lifetime and prevent donor-acceptor pair photo luminescence (DAP PL). A pronounced electron lifetime reduction when injection level approaches the doping level was observed. It is caused by diffusion driven non-radiative recombination. However, the influence of surface recombination is small and insignificant at 300 K