Mixed crystals trap depth

Fig. 2. The energy levels as a function of trap depth S for the onedimensional mixed crystal with guest concentration The manifold shown belongs to r = 0. The dotted curves are plots of the shallow-trap (left-hand) and deep-trap (right-hand) limiting approximations.

Fig. 3. Schematic diagram of levels in a one-dimensional mixed crystal containing several guest molecules. One level from each manifold moves out of the band, finally coalescing at large trap depths.

In the inverted band a quite different pattern of intensity distribution is to be expected. In the pure crystal the topmost level alone is active it remains the strongest under all conditions. As the trap is deepened, some intensity moves from the topmost level downward through the band into the bottom level, which breaks out of the band and eventually becomes practically a localized state of the trapping molecule. Thus the presence of guest molecules awakens spectral activity in normally inactive levels, and should enable the extent and character of the pure crystal band structure to be studied experimentally. The point is illustrated in the diagrammatic spectra in Fig. 6, illustrating the transitions in one-dimensional mixed crystals for trap depths from zero (pure crystal) to d = 3.6. In each case the intensities are adjusted to make the lowest transition have unit intensity this... 

Fig. 6. Schematic absorption spectra of one-dimensional mixed crystals, m = 6, with inverted bands, for various trap depths (5. The intensities are adjusted to give equal values in the third transition, except in the top (pure crystal) spectrum. Hatching indicates very intense absorption.

Sensitised emission in isotopic mixed crystals at higher (> 1%) concentrations Exdton transfer in dilute exdton systems kfjG D in dilute exdton systems S,T Intensity of the guest emission with varying trap depth in isotopic mixed crystals as... 

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