Sequential Thermal Decomposition of the Shell of Cubic ZnS/Zn(OH)<sub>2</sub> Core–Shell Quantum Dots Observed With Mn<sup>2+</sup> Probing Ions

Thermally induced changes in the structure and composition of the shell of tightly aggregated cubic ZnS/Zn­(OH)<sub>2</sub> core–shell quantum dots of 1.9 nm average core size were investigated by multifrequency electron paramagnetic resonance of Mn<sup>2+</sup> probing ions. The observed three-steps temperature induced transformation of the Mn<sup>2+</sup> surface centers in the 80–450 °C temperature range was attributed to the sequential decomposition by dehydration of the disordered ε-Zn­(OH)<sub>2</sub> shell into ZnO, with the formation of the Zn<sub>2</sub>O­(OH)<sub>2</sub> and Zn<sub>4</sub>O<sub>3</sub>(OH)<sub>2</sub> intermediate nanocompounds. The presence of a 0.3 to 1.9 nm thick surface layer of disordered nanomaterial separating the cubic ZnS cores and its shrinking to a few atomic layers by mass loss after annealing up to 350 °C was observed by high resolution transmission electron microscopy. Unlike the single step dehydration around 120 °C of the bulk ε-Zn­(OH)<sub>2</sub>, the complex decomposition of the ε-Zn­(OH)<sub>2</sub> shell is attributed to its nanosized, disordered structure.