Quantum yield absolute measurement with integrating

Absolute luminescence quantum yield measurements are not made in photophysical practice and are left to specialized laboratories such as the National Physical Laboratory (UK) or the National Bureau of Standards (USA). These provide the quantum yields of a variety of primary standards that are used in practice to determine an unknown quantum yield e. First the luminescence spectrum of the primary standard is measured, and then that of the unknown sample is compared with it as the ratio of the integrated spectra. 

The primary quantum yield has been found to be unity for a wavelength integrated measurement in the interval 174 to 210 nm (50). With a high-pressure Xe continuum source filtered at the short wavelength end by an atmosphere of air and at the long-wavelength end by the declining absorption coefficient of CO2 itself, a value of 1,0 0.25 was obtained for CO production. Resonance fluorescence of the CO Fourth Positive system was employed to measure the yield of CO, and absolute... 

The absolute measurement of the quantum yield is very difficult because of the geometry of the emission and the presence of re-absorption. It is usually measured by direct comparison with samples with know quantum yields, or by using an integrating sphere. However, by considering negligible the temperature dependence of the absorption cross section (Demtrdder, 1996 Menzel, 2001) ... 

The factor kr is temperature-independenL The non-radiative rate constant contains contributions from a temperature-independent term, which accounts for the deactivation to the ground state, and a temperature-dependent term which can play a role when upper-lying short-lived excited states are thermally accessible (Thompson et al., 2002). Determination of quantum yields is not an easy task. The measurement of absolute quantum yields is critical and requires special equipment, because it is necessaiy to know the amount of excited light received by the sample. These measurements are done by the use of scattering agents and integrating spheres to calibrate the system. For routine woik, one is often satisfied with the determination of relative quantum yields. In this case the quantum yield of the unknown is compared with that of a reference sample ... 

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