Luminescence Quantum Yield Measurements

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 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. 

This ratio gives the relative quantum yield, or the absolute quantum yield so long as that of the standard is accurate. There are some essential conditions to be met. 

This method of luminescence quantum yield measurement against a standard emitter is simple and easy to implement with computer-linked fluorimeters, in particular for the integration of the spectra. Its accuracy should however not be over-rated. It is, in the best cases, of the order of 5% (and often far worse). It remains at this time the most widely used technique in photophysics. 

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Overall luminescence quantum yields measured in the corresponding deuterated solvent. 

Several luminescent ( 650 nm) dioxorhenium(V) systems(25) have been investigated as potential 0-atom transfer agents. The emission quantum yields measured with 436 nm excitation are about 0.03 for trans-ReO (pyridine)u and its isotopically-substituted derivatives in pyridine solution. The excited state lifetimes of these ions vary from 4 to 17 ys. 

X -Ray powder pattern studies of the complexes [M(phen)2X2]" and [M(bipy)2YZ]"+ [M = Co, Rh, Ir, or Os X = Cl, H2O, or ox YZ = CI2 or (0H)(H20)] show that each metal in each series is isomorphous. A cis configuration is therefore assigned to all complexes. Luminescence quantum yields have been measured for a series of [IrCl2(N—N)2C1 complexes (N—N = phen or bipy, or diphenyl derivatives), permitting a quantitative estimate of the effect of ligand phenyl substituents.A normal-co-ordinate analysis (i.r. has been carried out for [Ir(NH3)5Cl]Cl2. ... 

In another study, Kondrat eva (103) made a determination of the luminescent quantum yield of the 5D4 state of the terbium ion in aqueous solution. The method used was based upon fluorescent-lifetime measurements and had previously been used by Rinck (96) and Geisler and Hellwege (96) to determine the quantum yield of rare earths in crystals. Kondrat eva made his studies on chloride and sulfate solutions, using the electronic shutter technique of Steinhaus et al. (66). 

When heat is produced in the sample after the photolytic flash, the refractive index of the liquid changes and the probe beam is deflected. The intensity of this probe beam measured by a photomultiplier tube placed behind the pinhole decreases as the temperature of the irradiated volume increases (then its density and its refractive index decrease). The total optical signal change is a measurement of all the heat produced in the sample, i.e. the sum of non-radiative transitions, chemical reactions and solvation energies. Luminescence does not contribute to this signal (nor does scattered light) and for this reason thermal lensing can be used to determine luminescence quantum yields. 

The measured intensity is a function of the total number of excited species created by the excitation pulse and of the luminescence quantum yield, Q. In other words, for a given lifetime, the Q value determines the ease of detection of a given species. The notion of radiative vs. non radiative pathways is in fact very important as will be detailed below (sects. 3-5). 

The 4G5/2 -> 6Hc>/2 transition of Smm (2-hydroxyisophthalamide) macrobicyclic complex with Q n = 0.073% in 0.01 M tris buffer (Petoud et al., 2003) has been used as a reference for the [Yb(84a)4]- complex, this latter being itself taken as standard for the quantum yield measurements of Ndm and Er111 complexes. For Ho111 and Tmm, the [Er(84a)4] complex was used as standard because of their comparable luminescence intensities. The quantum yields obtained are clearly dependent on the nature of the solvent, suggesting that the Lnm... 

Quenching mechanism. Steady state measurements of the luminescence quantum yield of Ru(byp)3 intercalated in clay films brings about more detailed information with respect to the possible role of electron transfer in luminescence quenching. The quantum yield is dependent upon the amount of co-adsorbed water and s strongly depleted by transition metal impurities, such as Fe5 or Cr in the lattice (28). 

A basic problem which can be encountered in the application of photophysics to colloidal systems are difficulties involved in the measurement of true luminescence spectra and determination of luminescence quantum yields of molecules in light scattering media. Gade and Kaden have produced a theory for this effect which can be used to take account of readsorption and re-emission effects in suspensions. 

Vacuum-u.v. photolysis of N2O isolated in Ar matrixes at 4 K gives direct luminescent evidence for the photodissociative production of both 0( S) and N( D) atoms. The matrix results have been compared to relative atomic quantum yields measured in the gas phase. ... 

Measurements have been made of the room-temperature luminescence quantum yields of various Cr ammine and ethylenediamine complexes in water. Most emission was phosphorescence, but some fluorinated complexes emitted delayed fluorescence. The range of quantum yields was accounted for in terms of processes degrading the state. Radiationless decay rates for the transition... 

A single-photon counting technique has been used in the measurement of the luminescence quantum yields of chlorobenzene and benzyl chloride at 77 in a range of matrices [Of(CeH5Cl) = (1 0.5) x 10-1, ( 6 1) = (2 1) x... 

In contrast, radiative and especially nonradiative transition probabilities (Figure 3) can be very sensitive to environment. The evaluation of 2- 6 as a function of temperature and environment is the ultimate purpose of photophysical studies. The directly measurable quantities are the luminescence quantum yields ( ) and lifetimes (t) for fluorescence ( T2 A2) and for phosphorescence ( - 2)-... 

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