Structural changes in hydrocarbon-doped water-ice during amorphous to crystalline phase conversion are investigated using polycyclic aromatic hydrocatbons (PARS) as probes. We show that aggregation of impurity molecules occurs due to the amorphous crystalline transition in ice, especially when they are hydrophobic molecules such as PAHs. Using ultraviolet visible (UV vis), Fourier-transform Infrared (FTIR), and laser-induced-fluorescence (LIP) spectroscopic techniques, we show that, although ice infrared absorption features change from a broad structureless band corresponding to amorphous ice to a sharp structured crystalline ice bands, simultaneously, sharper isolated PAH UV absorption features measured in the amorphous ice host turn broad upon ice crystallization. A simultaneous decrease in the monomer fluorescence and increase in the excimer emission band is observed, a clear indication for the formation of PAR molecular aggregates when amorphous ice is converted to crystalline ice at higher temperatures. Similar to the irreversible amorphous crystalline phase transitions, the UV, fluorescence, and excimer,emissions indicate that PAH's undergo irreversible aggregation. Our studies suggest that organic impurities exist as aggregates rather than monomer's trapped in crystalline water-ice when cycled through temperatures that convert amorphous ice to crystalline ice, rendering a better insight into phenomena such as the formation of cometary crust. This aggregate formation also may significantly change the secondary reaction pathways and rates in impurity-doped ices in the lab, on Earth, in the solar system, and in the interstellar medium.