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Measurement of Scattering and Absorption Cross Sections of Dyed Microspheres



Adolfas Gaigalas, Steven J. Choquette


Measurements of absorbance and fluorescence emission were carried out on aqueous suspensions of polystyrene (PS) microspheres with a diameter of 2.5 µm. Microspheres with and without green BODIPY@ dye were measured. Placing the suspension inside an integrating sphere (IS) detector of a spectrometer yielded (after a correction for fluorescence emission) the absorbance (called A1 in the text) due to absorption by BODIPY@ dye inside the microsphere. An estimate of the absorbance due to scattering alone was obtained by subtracting the corrected BODIPY@ dye absorbance from the measured absorbance of a suspension placed outside the IS detector (called A1 in the text). The absorption of the BODIPY@ dye inside the microsphere was analyzed using an imaginary index of refraction parameterized with three Gaussian-Lorentz functions. The Kramer-Kronig relation was used to estimate the contribution of the BODIPY@ dye to the real part of the microsphere index of refraction. The complex index of refraction, obtained from the analysis of A3, was used to analyze the absorbance due to scattering (A1-A3 in the text) . The contribution from BODIPY@ dye was needed to properly model the scattering cross section measurements in the vicinity of the maximum of BODIPY@ absorption at 571 nm. The microsphere fluorescence quantum yield (QY) was measured and was found to be equal to the QY of green BODIPY@ dye in ethanol. The PS matrix does not quench the green BODIPY@ fluorescence. The maximum fluorescence emission and absorption of green BODIPY@ dye in microspheres were red-shifted by about 9 nm relative to BODIPY@ in ethanol.
Journal of Research (NIST JRES) - 118.002
Report Number


microspheres, dye, scattering, absorption, integrating sphere detector, Lorenz-Mie scattering, fluorescence quantum yield


Gaigalas, A. and Choquette, S. (2013), Measurement of Scattering and Absorption Cross Sections of Dyed Microspheres, Journal of Research (NIST JRES), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed May 24, 2024)


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Created January 14, 2013, Updated November 10, 2018