The excitation spectrum of phosphor is of special importance from theoretical and practical viewpoints. For a long time, the wavelength dependency of the ratio of fluorescence intensity of powdered phosphor to excitation intensity has been an object of interest called the excitation spectrum of powdered phosphor. The ratio
D of fluorescence intensity to excitation intensity, however, is varied in its absolute value and significance by not only the inherent characteristics of the phosphor but the experimental condition.
This paper deals with the excitation spectra of powderd phosphors when used for fluorescent lamps in which, because of multiple reflection on phosphor walls and of wavelength dependency of spectral reflectance of phosphors, the distribution of excitation energy and the absorption on phosphor walls are different from the case of single reflection.
From the results found on the absorption coefficient of powdered materials and the absolute value of the ratio
D, and by assuming appropriate values of scattering constant and thickness of phosphor wall, excitation spectra of several phosphors are calculated. In this calculation, the end effect of the lamp given by P. Moon's equation, the non-linearity of
D value in respect of excita-tion intensity and the possible change in quality of the phosphor during coating process are ignored.
With the scattering constant of 210 cm
-1 and the thickness of layer of 3mm, the
D value was found to increase when the reflectivity of phosphor is smaller than 0.5 but decrease when it is larger than 0.5.
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