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Ligand-free ZnO nanoparticles with a mean diameter of 100 nm were simply synthesized by solid-state transformation of Zn(II)–organic infinite coordination polymer particles (ICPs) at 550 °C. The well-crystallized ZnO nanoparticles exhibit strong visible emission centred at 600 nm and the emission light clearly appeared under UV light, representing the first example of strong, tunable and stable visible photoluminescence from relatively large ZnO nanoparticles both in solution and in the solid state. ZnO nanoparticles were synthesized by this approach without any surfactant or capping molecules and their visible emission is generally stable and remains almost unchanged while keeping samples in air for at least 3 months. The possible mechanism of strong visible emission was also proposed; oxygen vacancies and surface defects play an important role in the visible emission based on the results of electron paramagnetic resonance (EPR) spectra and decay lifetime curve. ZnO nanoparticles with strong visible emission centred at 500 nm could also be obtained by changing the compositions of coordination polymers. This solid-state transformation method provides a new approach to synthesize stable ZnO nanoparticles with strong and tunable visible emission by using coordination polymers.
Shi et al. (Sat,) studied this question.