news digest ♦ LEDs
experiment, Kent noticed that sharp emission lines characteristic of the element gadolinium could be controlled with electric current.
Different elements fluoresce at different wavelengths when they are excited, and gadolinium fluoresces most strongly at a very precise wavelength in the UV, outside of the range of human vision. The engineers found that the gadolinium-doped wires glowed brightly at several specific UV frequencies.
Exciting different materials to generate light is nothing new, but materials that glow in UV are harder to excite. The only other reported device which can electrically control gadolinium light emission requires more than 250 volts to operate.
The Ohio State team showed that in a nanowire LED structure, the same effect can occur, but at far lower operating voltages: around 10 volts. High voltage devices are difficult to miniaturise, making the nanowire LEDs attractive for portable applications.
“The other device needs high voltage because it pushes electrons through a vacuum and accelerates them, just like a cathode ray tube in an old-style TV. The high- energy electrons then slam into gadolinium atoms, which absorb the energy and re-emit it as light in the UV,” Myers explains.
“We believe our device works at significantly less voltage precisely because of the LED structure, where the gadolinium is placed in the centre of the LED, exactly where electrons are losing their energy. The gadolinium atoms get excited and emit the same UV light, but the device only requires around 10 volts.”
Because the LED emits light at specific wavelengths, it could be useful for research spectroscopy applications that require a reference wavelength, and because it requires only 10 volts, it might be useful in portable devices.
The same technology could conceivably be used to make UV laser diodes. Currently high-powered gas lasers are used to produce a laser at UV wavelengths with applications from advanced electronics manufacturing to eye surgery. The so-called excimer lasers contain toxic gases and run on high voltages, so solid-state lasers are being explored as a lower power and non-toxic alternative.
As to cost, Kent pointed out that the team grows its LEDs on a standard silicon wafer, which is inexpensive and easily scaled up to use in industry. “Using a cheap substrate is good; it balances the cost of manufacturing the nanowires,” he says.
80
www.compoundsemiconductor.net October 2013 Cree CR22 troffer
“We originally considered replacing the existing T8 fluorescent tubes with T5 fluorescents, but after testing Cree’s CR22 LED troffer, we knew it was the best solution for this installation,” says Tony Roberts, senior chief engineer supporting Piedmont Office Realty
The team is now working to maximise the efficiency of the UV LED, and the university’s Technology Commercialisation and Knowledge Transfer Office will license the design as well as the method for making specially doped nanowires to industry.
This research is described in detail in the paper, “
This research was sponsored by the National Science Foundation (NSF) and Ohio State’s Centre for Emergent Materials, one of a network of Materials Research Science and Engineering Centres funded by NSF.
NASA headquarters brightened up by Cree LED lights
Cree’s CR series of III-nitride based troffers deliver improved light quality with an estimated 52 percent savings in energy costs
The National Aeronautics and Space Administration (NASA) headquarters, a leased facility in Washington, D.C., has been outfitted with energy-saving CR Series LED Troffers by Cree.
The high-performance LED installation is part of a renovation to maximise energy savings of the 600,000 square-foot building.
More than 1,300 Cree CR22 architectural LED troffers have been installed, and Piedmont Office Realty Trust, owners of the NASA headquarters building, expects the new fixtures to deliver energy savings of 52 percent over the previously installed T8 fluorescent fixtures. An additional 5,200 Cree CR22 troffers are planned to complete the lighting upgrade.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142