Phosphorescence refraction index

The relatively simple study of fluorescence and phosphorescence (based on the action of colour centres) has nowadays extended to nonlinear optical crystals, in which the refractive index is sensitive to the light intensity or (in the photorefractive variety (Agullo-Lopez 1994) also to its spatial variation) a range of crystals, the stereotype of which is lithium niobate, is now used. 

Other techniques previously described for general investigation of tautomeric equilibria (76AHC(S1)1> involve heats of combustion, relaxation times, polarography, refractive index, molar refractivity, optical rotation, X-ray diffraction, electron diffraction, neutron diffraction, Raman, fluorescence, phosphorescence and photoelectron spectroscopy, and mass spectrometry. The application of several of these techniques to tautomeric studies has been discussed in previous sections. Other results from the more important of these will be referred to later in this section. 

Hydrostatic pressure up to 300 MPa had no effect on the absorption and emission spectra (2 = 511 nm) of Pt2(POP)4 in ambient temperature aqueous solution. There was a modest decrease in the phosphorescence lifetime from t = 8.8 ps at 0.1 MPa to 7.6 ps at 300 MPa and a corresponding 13 % decrease in the phosphorescence quantum yield (C>°- = 0.55, 0, = 0.48). Since the intersystem crossing to the LEES was estimated to be unity in both cases, these data demonstrate that pressure has little effect on k, (Eq. 6.9) [22], consistent with the relative insensitivity of the refractive index of water to pressure [23]. 

Here v is the wave number, e (v) the molar decadic extinction coefficient of the acceptor and (v) the spectrum of the donor emission (fluorescence or phosphorescence) measured in quanta per wave-number interval and normalized to unity on the same scale. N is the number of molecules per millimole, n the refractive index of the surrounding medium and the intrinsic life time of the excited donor state, k is a numerical factor representing the orientation dependence of dipole-dipole interaction. Its average is /2/3 = 0.816 for fast Brownian rotation of both molecules and 0.690 for random but rigid orientations . 

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