The development and demonstration of a highly efficient warm‐white all‐nitride phosphor‐converted light emitting diode (pc‐LED) is presented utilizing a GaN based quantum well blue LED and two novel nitrogen containing luminescent materials, both of which are doped with Eu 2+ . For color conversion of the primary blue the nitridosilicates M 2 Si 5 N 8 (orange‐red) and MSi 2 O 2 N 2 (yellow‐green), with M = alkaline earth, were employed, thus achieving a high luminous efficiency (25 lumen/W at 1 W input), excellent color quality (correlated color temperature CCT = 3200 K, general color rendering index Ra > 90) and the highest proven color stability of any pc‐LED obtained so far. Thus, these novel all‐nitride LEDs are superior to both incandescent and fluorescent lamps and may therefore become the next generation of general lighting sources. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Rapid improvement in light emitting diode (LED) performance and an annual multibillion dollar lighting market is motivating worldwide development of LED based illumination systems. In addition to the traditional figures of merit of efficiency and high flux density, the white LED lamps must also have appropriate color characteristics. Current commercial white LED lamps have undesirable color temperatures and uniformity, and inferior color rendering. As discussed below, color uniformity in single phosphor lamps has been improved by deposition of thin uniform phosphor layers conformal to the LED die. Also, 2-phosphor LED lamps with white color characteristics typical of conventional incandescent and halogen sources are described. Furthermore, LED illumination offers additional features not practically achievable with conventional sources.

Photoluminescence and cathodoluminescence properties of SrGa2S4 : Eu2+ thin films prepared by reactive RF magnetron sputtering are investigated. Luminescence performances of the phosphor in the thin film form are compared to those of powder samples: the brightness efficiency of thin films is found to be about 30% of the efficiency of powder at low current density. A ratio higher than 40% is expected at higher current density. Thin film screens for FEDs will become a positive alternative to powder screens provided that film quality and light extraction could be improved by optimization of thickness and deposition parameters.

There are numerous materials challenges involved in the production of high-efficiency III-nitride lasers and LEDs, some of which can be mitigated by epitaxy and device physics. The lack of a suitable lattice-matched substrate for epitaxy of AlInGaN films results in high dislocation densities and a large amount of residual strain in the deposited films. The role of the dislocations is not well-understood, although there is clear evidence that laser reliability is improved by reducing their density.

Phosphor conversion of blue radiation from InGaN LEDs has recently gone to a new quality: white light, which is illumination grade in the sense of high color rendering and color temperatures below 4000°K. At the same time power packages taking inputs of 1 Watt or even 5 W and surpassing in efficiency small size halogen lamps have been introduced. After a short review of alternative solutions state of the art devices are described and open questions outlined.

High-power, large-area InGaN/GaN quantum-well heterostructure light-emitting diodes based on an inverted, or "flip-chip", configuration are described. These devices are mounted in specially designed high-power (approximate to1-5 W) packages and exhibit high extraction efficiency and low operating voltage. In the blue wavelength regime, output powers greater than 250 mW (1 x 1 mm(2) device) and 1 W (2 x 2 mm(2) device) are delivered at standard operating current densities (approximate to50 A/cm(2)), corresponding to "wall-plug" efficiencies of 22%-23%. Employing phosphors for the generation of white light, these same devices achieve luminous efficiencies greater than 30 lm/W.

Green phosphor-converted LEDs using a blue pump InGaN diodes have advantages over the direct green InGaN LED with regards to color stability with drive and/or temperature. Added manufacturing steps are outweighed by higher color yield, as a range of pump colors can be used without changing the final chromaticity. The conversion losses can be smaller than the decrease in wall-plug efficiency from blue towards green, which has been reported by many sources. A distinct disadvantage of the concept is due to only one color and phosphor proven - SrGa2S4:Eu2+ and 535 nm peak wavelength.

High power light emitting diodes (LEDs) continue to increase in output flux with the best III-nitride based devices today emitting over 150 lm of white, cyan, or green light. The key design features of such products will be covered with special emphasis on power packaging, flip-chip device design, and phosphor coating technology. The high-flux performance of these devices is enabling many new applications for LEDs. Two of the most interesting of these applications are LCD display backlighting and vehicle forward lighting. The advantages of LEDs over competing lighting technologies will be covered in detail.

Phosphor conversion of light-emitting diode light for white light sources and some monochrome applications requires particular phosphor properties and has to take into account specific issues if aimed at high-power output. Limitations and solutions will be discussed, giving special considerations to drive and temperature dependencies. Efficiencies of 32 lm/W for white with good color rendering at 4600 K and 35 lm/W for green (535 nm) have been demonstrated.

White light for illumination can be produced from LEDs either by combining red, green and blue emitting chips in one lamp, or by using phosphors to down-convert the emission of short wavelength emitting InGaN LEDs. Both concepts will be critically reviewed, and simulations compared with experimental evaluations. As expected, each solution has advantages, but also drawbacks, which are weighted by the specifics of the applications. The overall picture strongly depends on the efficiencies of the single color chips, the temperature coefficients of all involved materials, and the wanted light output per lamp.

Blue electroluminescence is reported from CaS:TmF3 thin films prepared by radio frequency magnetron sputtering method. The dependences of brightness on substrate temperature, concentration of TmF3, and the applied voltage were investigated on alternating current thin-film electroluminescent devices. The obtained maximum brightness was above the level of ZnS:TmF3 devices. The equivalent average energy of the excited electrons contributed to the electroluminescence in CaS:TmF3 alternating current thin-film electroluminescent devices and was estimated at around 4.23 eV by comparing the ratio of infrared to blue peak in electroluminescent spectra with that in photoluminescent spectra excited by different photon energy. The excitation processes of electroluminescence in CaS:TmF3 thin films were assumed to be energy transfers from the conduction band edge to Tm3+ centers.

Abstract— Thin ZnS:Mn and SrS:Ce electroluminescent films are grown by solid‐source metal‐organic chemical vapor deposition (MOCVD). The method is attractive because it uses relatively non‐toxic materials and does not require flammable hydrogen or toxic H2S. Performance results are presented for both blue‐ and white‐emitting phosphors. Even though the method has not yet been optimized, luminous efficacy of 3 lm/W at low drive voltages has been attained for ZnS: Mn.