Real-time evolution of up-conversion nanocrystals from tailored metastable intermediates.

In-situ observation of the growth and decomposition processes is significantly important for guiding the fabrication of up-conversion nanocrystals (UCNCs) with high performance. However, the high crystallization energy and rapid nucleation rate of the corresponding crystals make real-time observation still a huge challenge. Herein, the in-situ nucleation-growth-degradation processes of the UCNCs are investigated by employing tailored metastable intermediates, which possess a slowing-down nucleation rate under electron beam irradiation. The non-classical nucleation processes of the UCNCs, containing the coalescence of clusters and the subsequent crystallization, are demonstrated. Moreover, the Ostwald ripening and oriented attachment processes, which determine the particle size and morphology, are unambiguously recorded. Furthermore, the degrading process of the UCNCs is observed to be triggered by surface defects. Our work provides an insight into the real-time evolution dynamics of the UCNCs, which further sheds light on the fabrication of nano-sized up-conversion phosphors. [ABSTRACT FROM AUTHOR]