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Investigations on thermal evolution of pairing-phase transition and shape-phase transition in light nuclei are made as a function of pair gap, deformation, temperature and angular momentum using a finite temperature statistical approach with main emphasis to fluctuations. The occurrence of a peak structure in the specific heat predicted as signals of the pairing-phase and shape-phase transitions are reviewed and it is found that they are not actually true phase transitions and it is only an artifact of the mean field models. Since quantal number and spin fluctuations and statistical fluctuations in pair gap, deformation degrees of freedom and energy when incorporated, it wash out the pairing-phase transition and smooth out the shape-phase transition. Phase transitions due to collapse of pair gap and deformation is discussed and a clear picture of pairing-phase transition in light nuclei is presented in which pairing transition is reconciled.

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The intent is to explore the optoelectronic properties of metal ions doped stilbazolium derivative, 4-N,N′-dimethylamino-N-methyl-4-stilbazolium tosylate (MnCl 2 -DAST) nonlinear optical crystal materials for the existing technological necessities. The Mn-DAST single crystals are crystallized by adopting the slow evaporation solution technique (SEST). The structural and crystallographic dimensions of grown crystals are affirmed using single-crystal X-ray diffraction and powder crystal X-ray diffraction. Fourier transform infrared spectra are performed to explicate the functional groups and energy dispersive X-ray analysis (EDAX) spectra confirm the presence of the chemical elements of grown crystals. The UV-vis absorption spectra of DAST and Mn-DAST crystals exhibit all possible n-* and -* electronic transitions. The blue shift is observed in the doped materials due to the exchange of lone pair electrons between the metal ions and organic molecule. Tremendously, the second order harmonic generation (SHG) efficiency of Mn (0.01 mol%) doped DAST crystals has 1.68 times larger than that of DAST crystal. From the metal-organic crystals (Mn-DAST), all the results brought out are the promising materials in the design of nonlinear optical applications.