Luminescence thermal quenching

Measuring the variations of the intensity ratio /inp/Zyb under pressure, Takarabe (1996) was able to determine the energy difference bt and found a pressure-induced shift of 70 meV/GPa which is close to the shift of the band-edge related luminescence due to the bound e-h pairs. Furthermore, under pressure it was possible to completely recover the thermally quenched luminescence of the Yb3+ ion at temperatures of 220 K and 260 K (Takarabe et al., 1994) as well as at room temperature (Takarabe, 1996). The minimum pressure at which the luminescence could be observed again was shown to increase with increasing temperature. All these facts fitted well to the proposed back-transfer model, which was thus strongly supported by the pressure experiments. 

The conventional theory of thermal quenching by excitation of a carrier out of a shallow trap predicts a thermally activated process. No single activation energy is observed in a-Si H, but it is found that the luminescence efficiency, follows the relation (Collins, Paesler and Paul 1980),... 

The average of 10 s gives /23, so that the measured value of 20-25 K is of the correct magnitude for the band tail slope in a-Si H. The larger in the alloys is because they have broader band tails. The derivation of Eq. (8.46) makes several approximations, of which the most severe is the neglect of the distribution of lifetimes, so that one should not expect an accurate fit. Also it is tacitly assumed that only one type of carrier is thermally excited. The non-radiative process obviously involves both carriers. The question of what is the rate-limiting step in the process is complicated and, in fact, the thermal quenching of the luminescence depends on the defect density and on the excitation intensity. 

Evidence for the Auger process is contained in the low temperature luminescence data in Fig. 8.19 (Street 1981b). The thermal quenching... 

Table 2 Main families of luminescent ions, nature of transitions, and order of magnitude of radiative lifetimes (values at 300 K, except for the charge transfer (CT) emission of Ce + and Yb + whose emission is affected by thermal quenching at room temperature)...

Thermal Quenching of the Uranate Luminescence of Ordered Perovskites A2BW06-U + ... 

In our opinion this shows that the thermal quenching temperature of the luminescence of the closed-shell complexes depends more strongly on the energy difference between the parabolae than on their offset ). In fact only the colourless complexes are able to show luminescence of any importance. 

Let us now turn to a discussion of the thermal quenching temperature, Tq, of the luminescence. Its value varies significantly as a function of the host lattice, the... 

Fortunately, it is not necessary to include all the excited states in the model describing the thermal quenching of the uranate luminescence. In order to explain the... 

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