Phosphorescence is much slower about 1 to 10 6 sec

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Phosphorescence is much slower, about 1 to 10 -6 sec. This is because the electron has undergone spin inversion. Remember the Pauli Exclusion Principle. What if we have a sample holder known as a cuvette in the path of Electromagnetic radiation of some energy:
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If the incident light has an incident power, P o , and the exiting light has intensity, P , then the transmittance through the path length b (cm) of the sample is: T = P/P o (Range of 0 to 1) The absorbance at that wavelength is: A ( λ ) = -log( P / P o ) = -log( T ) If we do some calculus, we come up with the Beer-Lambert Law : A ( λ ) = ε λ b C (dimensionless) Beer's Law will deviate at high concentrations of analyte. Solvent is chemically affected by high concentrations of analyte, thus impacting ε The distribution of analyte components as a result of equilibria events is drastically affected by high analyte concentrations An absorption spectrum is a graph showing how A varies with λ .
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Note: Any substance that absorbs visible light will appear colored when white light is transmitted through it or reflected from it. The substance absorbs certain wavelengths of the white light, and our eyes detect the wavelengths that are not absorbed. The observed color is called the complement of the absorbed color. The Absorption Spectrophotometer Light from a continuous source is passed through a monochromator . This monochromatic light travels through a sample of pathlength b, and the radiant power of the emergent light is measured. Visible light generated from a quartz halogen lamp. UV light generated from a deuterium arc lamp. cuvette – sample cell that has flat quartz faces. Quartz transmits both UV and visible light – plastic or glass only transmits visible light. Single-beam spectrophotometer First measure P o for a reference cuvette containing pure solvent. Then replace reference cuvette (containing the blank) with cuvette containing sample to measure P. Block Diagram of Single-beam Spectrophotometer Inconvenient, somewhat inaccurate, poorly suited to continuous measurements Double-beam spectrophotometer Light passes alternately through the reference and sample cuvettes. A chopper is a mirror that rotates in and out of the light path diverting the light between the reference and sample cuvettes. Routine procedure is to first record a baseline spectrum with two reference cuvettes. The absorbance of the reference is then subtracted from the absorbance of the sample to obtain the "true" absorbance at each wavelength.
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Precautions Most spectrophotometers operate best at values for A 0.4 – 0.9 If absorbance too high, intensity is hard to measure. If absorbance too low, hard to distinguish between reference and sample Slight mismatches between reference and sample cuvettes leads to systematic error Samples must be dust free. Cuvettes must be wiped clean before use.
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