A design methodology for phosphor mixtures for tunable spectrum LEDs
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A design methodology for phosphor mixtures for tunable spectrum LEDs Partha S. Dutta and Kathryn M. Liotta MRS Advances / FirstView Article / August 2016, pp 1 - 6 DOI: 10.1557/adv.2016.548, Published online: 11 August 2016
Link to this article: http://journals.cambridge.org/abstract_S205985211600548X How to cite this article: Partha S. Dutta and Kathryn M. Liotta A design methodology for phosphor mixtures for tunable spectrum LEDs. MRS Advances, Available on CJO 2016 doi:10.1557/adv.2016.548 Request Permissions : Click here
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MRS Advances © 2016 Materials Research Society DOI: 10.1557/adv.2016.548
A design methodology for phosphor mixtures for tunable spectrum LEDs Partha S. Dutta1,2 and Kathryn M. Liotta1 1
Smart Lighting Engineering Research Center, Rensselaer Polytechnic Institute, Troy, New York, 12180, USA 2
Auterra Inc, Schenectady, New York, 12308, USA
ABSTRACT Spectrum tuning in phosphor converted white light emitting diodes (pc-WLED) is done by mixing powders of phosphor compounds (with different emission wavelengths) in different weight ratios. In this paper, a new methodology for designing unique full spectrum phosphor mixtures (with fixed weight ratios of different emission phosphor) has been presented that could provide a wide range of pc-WLED spectrum. This is done by optimizing the excitation and emission spectra of the phosphor compounds used in the mixture. A unique phosphor mixture comprising of Eu2+ and Ce3+-Na1+ activated compounds of SrGa2S4, CaGa2S4, SrS, CaS and CaF2 was used to produce full spectrum warm, neutral and cool white LEDs with color temperatures between 2500 K and 7500 K and with color rendering index exceeding 95. INTRODUCTION Phosphor based LEDs provide the unique feature for tailoring the emission spectrum necessary for the next generation of advanced lighting and display applications [1-10]. Specifically, artificial lighting mimicking natural light (sunlight) and displays with full spectrum backlighting units are anticipated to significantly improve the cognitive psycho-physiological health of human beings. The color temperature of a white light source is based on its emission spectrum. In case of the pc-WLED, the emission spectrum can be altered by mixing different amounts of phosphor powders with emission wavelengths in the blue, cyan, green, yellow, orange and red parts of the visible light spectrum [1-4]. Figure 1 (a) shows schematically how the color temperature is varied from cool white to warm white in commercial pc-WLEDs. In cool white LEDs, a part of the blue light from the GaInN excitation source (blue/near UV LED) escapes through the yellow emitting phosphor layer. The rest of the blue light is absorbed in the phosphor layer and reemitted (wavelength down converted) as yellow emission. When the blue and yellow emissions combine, it produces the whi
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