Luminescence deconvolution

Natural minerals may contain simultaneously up to 20-25 luminescence centers, which are characterized by strongly different emission intensities. Usually one or two centers dominate, while others are not detectable by steady-state spectroscopy. In certain cases deconvolution of the liuninescence spectra may be useful, especially in the case of broad emission bands. It was demonstrated that for deconvolution of luminescence bands into individual components, spectra have to be plotted as a function of energy. This conversion needs the transposition of the y-axis by a factor A /hc (Townsend and Rawlands 2000). The intensity is then expressed in arbitrary imits. Deconvolution is made with a least squares fitting algorithm that minimizes the difference between the experimental spectrum and the sum of the Gaussian curves. Based on the presumed band numbers and wavelengths, iterative calculations give the band positions that correspond to the best fit between the spectrum and the sum of calculated bands. The usual procedure is to start with one or... 

Deconvolution. When the luminescence lifetime is close to the laser pulse duration, the kinetics can still be obtained by a process known as deconvolution, so long as the luminescence decay is exponential. The deconvolution program is a computer simulation of the shape of the laser pulse modified for various luminescence lifetimes. An example is given in Figure 7.33. The kinetics of fluorescence decay could not be resolved directly, but it is clear that the emission pulse shape differs from the laser pulse shape... 

Typically, in measurements of time-resolved luminescence in the time regime of tens of picoseconds, data obtained from 10 to 20 laser shots are averaged to improve the signal-to-noise ratio and to minimize the effects of shot-to-shot variations in the laser pulse energy and shape. Once the reliability of the data has been ensured by application of the corrections described above and made necessary by detector-induced distortions, the time-resolved fluorescence data is analyzed in terms of a kinetic model which assumes that the emitting state is formed with a risetime, xR, and a decay time, Tp. Deconvolution of the excitation pulse from the observed molecular fluorescence is performed numerically. The shape of the excitation pulse to be removed from the streak camera data is assumed to be the same as the prepulse shape, and therefore the prepulse is generally used for the deconvolution procedure. Figure 6 illustrates the quality of the fit of the time-dependent fluorescence data which can be achieved. 

The deconvolution of multicomponent fluorescence spectra may be accomplished using a ratio method providing spectral regions may be located where the luminescence is due to one species only. ... 

The time-resolved luminescence of [Ru(bpy)3] has been deconvoluted into two components, and these have two different emission maxima (83). This observation suggests the existence of two distinct adsorption sites for [Ru(bpy)3] on laponite. At one type of the adsorption zone the water is held rigidly and presents an environment for the [Ru(bpy)3] probe that results in a short lifetime and a blue-shifted emission. The second absorption zone involves a stronger interaction directly with the clay surface such that the photophysics are less influenced by the nature of the surrounding water. This explanation was supported by a direct comparison of photophysical properties of the luminescence probe on the clay and in ice at - 20°C. 

The time correlated single photon counting technique allows the measurement, with great accuracy, of the luminescence emission lifetimes in a temporal range spanning from hundreds of picoseconds to tens of microseconds. As we have seen the shorter lifetimes are accessible by using the deconvolution procedure while the longer lifetimes are measurable by a suitable reduction of the excitation lamp frequency in order to avoid the presence of two or more excitation pulses within the selected excitation-emission time cycle. 

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