Ceramic Phosphors for Light Conversion in LEDs
| Autor: | Yi Zheng, Madis Raukas, John F. Kelso, A. Linkov, Krister Bergenek, Dominik Eisert, Frank Jermann |
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| Rok vydání: | 2012 |
| Předmět: | |
| Zdroj: | ECS Journal of Solid State Science and Technology. 2:R3168-R3176 |
| ISSN: | 2162-8777 2162-8769 |
| Popis: | In the present article we briefly review some materials research aspects related to ceramic phosphors and discuss both typical characteristics as well as unique features of such optical converters. Devices with more efficiency and/or higher luminous flux that are based on converting the pump light crucially enable the use of LEDs in white and single color illumination schemes for many applications. Advantages of generating white light with ceramics versus powder-in-silicone are discussed. High performance of single color conversion LEDs in terms of efficacy and external quantum efficiency for the visible region boost the output in data or With a significant rise of activities in Light Emitting Diode (LED) related applications (mobile phone and display backlighting, automo- tive front and signal lights, data projection and general illumination sources) over the past 15-20 years, the need for phosphor materi- als capable of converting the pump energy into radiation in different regions of the visible spectrum has received another boost. Simi- larly to development of luminescent materials in previous periods for X-ray, electron beam (Cathode Ray Tube) and ultraviolet (UV) exci- tation (e.g. in fluorescent lamps), the development of new phosphors for what industry refers to as Solid State Lighting (SSL) has produced a multitude of chemical compositions and application technologies to be used in conjunction with tiny semiconductor devices (electrically pumped chips) that produce near-UV or blue light. The same under- lying principle that light perceived by humans as 'white' consists of single color components ('blue', 'green', 'yellow' and 'red' in a sim- plified manner) does apply here like elsewhere. Many comprehensive reviews exist 1 for learning about the history of phosphors and there- fore this general subject will not be reviewed here. Different classes of materials from oxides to halides to sulfides and mixed ligand cases have been developed. Metal nitrides could be considered as one of the latest additions to this family, thanks to a more covalent nature of the bonding that enables color tuning of electronic transitions of Rare Earth (RE, typically europium and cerium) activators to lower energies than is possible with oxygen and other ligands. Like in sul- fides, the 4f-5d absorption of REs may extend to green and yellow wavelengths and the corresponding emission as far as deep red. The appearance of efficient blue LED pump sources enabled the simplest, "cold white" light generation scheme using a single yellow phosphor, for which cerium-activated yttrium aluminum garnet (Y3Al5O12 )i s perhaps the most ubiquitously used one around the world. The dis- covery of luminescent nitrides allowed adding efficient and stable broad band red emitters (e.g. M2Si5N8 ,M AlSiN3 and others where M=Ca,Sr or Ba based on Eu 2+ activation 2,3 and references therein). The red phosphors, along with other color components, contribute to producing higher quality light sources with lower correlated color temperatures (CCT) and higher color rendering index (CRI). 4 |
| Databáze: | OpenAIRE |
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