System-Level Thermal Phenomena

Recently, we also observed an anomalous thermalization phenomenon in Er Gd203 (1 at%) nanocrystals with diameters of 40-50 nm. In the excitation spectra at 2.9 K, hot bands originating from the upper stark level of 4Ii5/2 (38 cm-1) were observed. These hot bands disappear when temperature goes up to 5 K. Our preliminary results show that the anomalous thermalization phenomena in this system are more complicated, because they depend on the laser power and temperature. The effect of laser heating or temperature fluctuation in nanocrystals must be ruled out before a definite conclusion can be reached. 

Some of the investigations carried out in the first half of the twentieth century were related to CL associated with thermal decomposition of aromatic cyclic peroxides [75, 76] and the extremely low-level ultraviolet emission produced in different reaction systems such as neutralization and redox reactions involving oxidants (permanganate, halogens, and chromic acid in combination with oxalates, glucose, or bisulfite) [77], In this period some papers appeared in which the bright luminescence emitted when alkali metals were exposed to oxygen was reported. The phenomenon was described for derivatives of zinc [78], boron [79], and sodium, potassium, and aluminum [80]. 

When partially hydrated samples are cooled down to 77 K, no crystallization peak is detected by differential thermal analysis. The x-ray and neutrons show that an amorphous form is obtained and its structure is different from those of low-and high-density amorphous ices already known [5]. Samples with lower levels of hydration corresponding to one monolayer coverage of water molecules are under investigation. This phenomenon looks similar in both hydrophilic and hydrophobic model systems. However, in order to characterize more precisely the nature of the amorphous phase, the site-site partial correlation functions need to be experimentally obtained and compared with those deduced from molecular dynamic simulations. 

The entrapment of the Pc complexes in the zeolitic environment renders them thermally more stable. The only weakness of such systems consists in the limited access of large molecules via the 12-membered ring orifices of the faujasitc structure. The unprecedented properties of VPI-5 as support for MePc, showing a limited number of MePc complexes at the pore months, though unclear at the mechanistic level, might remediate this reduced accessibility, though the phenomenon requires more work to clarify its mechanism and estimate its potential. 

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