Sulfide Phosphors for LED White Light Sources
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0916-DD02-02
Sulfide Phosphors for LED White Light Sources Dongdong Jia1, Anura Goonewardene1, Weiyi Jia2, Xiaomei Guo3, Yingyin K. Zou3, and Kewen Li3 1 Physics and Geology, Lock Haven University of Pennsylvania, Lock Haven, PA, 17745 2 Physics, University of Puerto Rico, Mayaguez, PR, 00681 3 Boston Applied Technology, Inc., Woburn, MA, 01801 ABSTRACT Several sulfide phosphors, such as CaS:Ce3+,Na+, CaS:Eu2+,Ce3+, ZnS:Te,Mn, ZnS:Se,Te,Mn and ZnS:Ce,Li were prepared and their excitation and luminescent spectra were investigated. The possible applications in LED-Phosphors white light devices are discussed. INTRODUCTION LED-phosphor (LED-P) white light sources have been intensively investigated in the last decade.1,2 Two types of devices have been proposed initially.1 One is a combination of blue phosphor plus yellow-band phosphors. The other is to use UV LEDs (380-410nm) and tricolor phosphors with emission bands around 450, 520 and 650nm. However, from consideration of energy efficiency, the type of LED-tri-phosphors devices is likely not adaptable. Even for tricolor phosphors with 100% quantum efficiency, the energy conversion rate of 380nm photons to the above three colors is only 72%. Therefore, this type of devices is less attractive. In the current commercial LED-P products, blue LEDs are used. Part of the blue emission at 450-465nm is used as the blue component of white light and the other part is downconverted into yellow/red emission via the phosphors. At present, Y3Al5O12:Ce3+ based phosphors are the only materials to be used.3 No other materials have been tested. In this work, we present some spectral results of CaS:Ce3+,Na(Li), which shows similar luminescence and excitation spectra as YAG:Ce. It can be a good candidate for phosphors used in LED-P white light devices. In addition, spectroscopic results from other sulfides, including ZnS:Ce,Li, CaS:Eu,Ce, and ZnS:Te/Se,Mn are also investigated. The last two phosphors can be used to improve color rendering of LED-P devices. EXPERIMENTAL DETAILS Samples were prepared by the solid state reaction method. The raw materials used were CaS, Ce2(CO3)3:5H2O, Na2CO3 (Li2CO3), Eu2O3, ZnS, ZnSe, ZnSTe, MnCO3, NH4Cl, and S. NH4Cl was used as a flux, and S was used for sulphuration of oxides. The corresponding precursors were mixed with required amounts, and ground in an agate motar for about 10 minutes, and then pressed into pellets. CaS:Ce,Na and CaS:Ce,Eu pellets were sintered at 1200°C for one hour in N2 flow. ZnS samples were sintered at 1100°C for one hour in N2+5%H2 flow. Fluorescence and excitation spectra were measured at room temperature with a SPEX FluoroMax2. For low temperature measurements, an argon laser with emission at 457.9nm, a SPEX double grating spectrometer 1403 and a RMC Cryostat were used.
RESULTS AND DISCUSSION (1) CaS:Ce3+,Na+
Fig. 1 shows the luminescence and excitation spectra of CaS:0.1%Ce3+, 0.1%Na+. Na (or Li) is used for charge compensation. It can be seen that the spectra are similar with the spectra of YAG:Ce3+. The emission consist
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