Luminescence from ultrasonic

A follow up work by Brotchie et al. [42] noted that the resonance sizes of sono-luminescence and sonochemically active bubbles are different. The sonochemilu-minescence, resulting from the reaction between OH radicals generated within cavitation bubbles and luminol molecules, intensity was used to determine the sono-ehemically active (SCL) bubbles. The resonance size of SL bubbles are found to be relatively larger than that of SCL bubbles. In addition, Eq. (1.2) shows that the resonance size decreases with an increase in ultrasonic frequency. Brotchie et al. [42] have also confirmed this experimentally. The sizes were found to be 3.9, 3.2, 2.9, 2.7 and 2 pm at 213, 355, 647, 875 and 1056 kHz frequency, respectively. Another important aspect that needs to be mentioned is the difference between theoretical and experimentally determined resonance sizes of the cavitation bubbles. Equation (1.2) provides a theoretical value of 14 pm at 213 kHz whereas the experimental value is found to be 3.9 pm. This is also known from single bubble work at 20 kHz where the experimental resonance size was found to be about 5 pm compared to the theoretical value of 150 pm [43]. The difference between the resonance size determined by Eq. (1.2) and experimental value is due to the fact that Eq. (1.2) is a very simplified one that does not consider the physical properties of the liquid or bubble contents. 

The research focused on the use of MOFs in sensors is limited by the very recent (2006-2013) publications related to the luminescence, such as quenching of the nanosheets of Zn(BDC) MOF upon submission of ethylamine [222,223]. The emission at 446 nm was ascribed to the fluorescence from intraligand emission excited states. The morphology of such an MOF sensor (nanobelts, nanosheets, single crystals) was varied by applying different ultrasonic conditions in the synthesis. In general, d elements (like Zn+ or Cd+ ) deserve special attention in this concern, as they are known to exhibit strong fluorescence in the solid state. 

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