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The Absorbance, A, is the logarithmic value (to the base of 10) of the inverse of the Reflectance. The Reflectance, R, is the ratio of the scattered signal from the total diffuse reflecting standard and the sample. The following quantities can now be calculated: The area of the blue graph (starting from the base line) is here referred to as E Ref, the red hatched area will be E Sam and the red solid area is called L Sam. This sample shows reflection (red, hatched) and emission (red, solid). The second scan (red) is a scan of the sample under investigation. The first scan (blue) is a scan of a reference scatterer, which should have diffuse reflectance of 100%. The picture below graphically demonstrates two spectral scans made by scanning the emission monochromator, with the excitation monochromator fixed at 450nm. Theory of Reflectance, Absorbance, and Quantum Yield Measurements A small elliptical mirror and a baffle plate are fitted to the upper half, for beam steering and shielding against directly detected light. The upper half of the sphere needs to be removed for sample exchange. The lower half contains a pillar that has a small dish for the exchangeable powder tray. The lower half is tightly fitted to the base of the sample holder by means of two thumb screws. The procedure of exchanging the two sample holders takes less than 3 minutes. No lens is required in the emission channel. The two lens assemblies that are used for the standard sample holder have to be removed, and a special lens has to be inserted into the excitation path. The sphere replaces the standard sample holder inside the sample chamber. The integrating sphere for powder measurements (part number: 1-M-3) has been designed to meet the specific requirements for the measurements of spectral reflection, absorption and quantum yield of powders. In addition, powder samples are ideally measured with the powder positioned on a tray and the excitation beam pointing downwards, normal to the sample.
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This removes ambiguities due to angular dependences, it increases repeatability of alignment when changing between samples and it is beneficial for the overall reproducibility.
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Accura te Quantum Yield Measurements as well as precise measurements of the spectral dependence of reflection and/or absorption of powder samples, require an integrating sphere.