Optical Properties of Alkali Doped Group IV Nano Materials
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0916-DD03-03
Optical Properties of Alkali Doped Group IV Nano Materials Hal Gokturk Panasonic Electric Works Laboratory of America, 550 S Winchester Blvd #402, San Jose, CA, 95128
ABSTRACT
Optical properties of sodium and other alkali metals (lithium & potassium) incorporated into nano hosts of group IV elements (carbon, silicon & germanium) were investigated as candidates for solid state light emitting materials. First, optical properties were calculated by quantum mechanical simulations using TDDFT method. Results of the simulation indicate that alkali doped group 4 nano hosts exhibit optical transitions in and around the visible whereas, undoped nano hosts do not have any at similar wavelengths. Some combinations of alkali dopant and nano host give rise to multiple transitions in the visible. One of the simulated combinations, Li dopant and carbon nano host was synthesized for experimental verification. Optical absorption and emission characteristics of the synthesized material were measured and compared with those obtained from quantum mechanical calculations. Both the wavelength and the relative intensity of the measured optical transitions were found to be in good agreement with the results of the calculations. Alkali metals which have good light emission characteristics can be combined with group IV indirect semiconductors to obtain new nano materials which have interesting optical properties in the visible.
INTRODUCTION
Sodium is well known for its efficient optical transitions in the visible and it is utilized extensively in lighting applications. High pressure sodium lamps are the most efficient light sources with an efficacy reaching up to 140 lumen/watt, well above those of fluorescent lamps [1]. However the sodium in the lamp must be vaporized and excited by means of a plasma in order to emit light. Hence it is not possible to ignite a cold sodium lamp instantly to full brilliance. Warm up takes several minutes, and if the power is interrupted, a cool down period of several more minutes is necessary before the lamp can be turned on again. If sodium and possibly other alkali metals which have similar optical properties can be used in solid form, these efficient emitters can be used in solid state lighting. The method of excitation used in commercial sodium lamps is the collision of gaseous particles in the plasma. This method is not the most efficient way to excite the material, since the range of energies in the plasma is very broad. According to Ref. 1 about 70% of the energy input of a sodium lamp is wasted. If sodium can be excited with a narrow range of energies matched to its absorption peak, such as optical excitation by a light emitting diode, an efficacy much higher than the 140 lumen/watt can be expected.
In this research, optical properties of sodium and other alkali metals (lithium & potassium) incorporated into nano hosts of group IV elements (carbon, silicon & germanium) were investigated as candidates for solid state light emitting materials. Generally alkali metals exhibit ionic ty
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