Practical Measurements of Absolute Quantum Yields

Quantum yield measurements are simple in their principle, but very difficult to carry out experimentally, particularly when it comes to the luminescence of lanthanide ions and to intrinsic quantum yield, f-f absorptions being faint. There are two main methods the comparative method in which the sample under examination is compared to a standard with known quantum yield, and the absolute method which 

In the comparative method, the quantum yield of the unknown sample (indices x) is given relative to the quantum yield of the standard (indices S) by  

In case Ax A and at least one of them is 0.05, then the absorbances in (27a-c) should be replaced by  

It is also essential that emission spectra are corrected for the instrumental function estabUshed with a standard calibrated lamp. It is wise not to use the calibration curve given by the manufacturer of the spectrometer and to re-measure this instrumental function at regular intervals because many items influence it, particularly the emission intensity of the excitation lamp and the quantum efficiency of the detector (which both decrease with time). In case (27a) is used, the excitation instmmental function has to be known as well. Regarding the standard, it is best when its emission spectrum overlaps the emission spectmm of the unknown 

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