Multi-color luminescent ZnO nanoparticles produced by pulsed laser ablation in water

One of the most intriguing challenges of nanophotonics is the development of materials with controlled physical/chemical properties favorable for highly efficient and color tunable lighting. To this purpose, ZnO is a material... [ view full abstract ]

One of the most intriguing challenges of nanophotonics is the development of materials with controlled physical/chemical properties favorable for highly efficient and color tunable lighting. To this purpose, ZnO is a material of choice: the direct bandgap (E_g=3.4 eV) and the large exciton-binding energy (60 meV) allow the observation of an UV emission even at room temperature; in addition, defects in the ZnO network introduce deep-levels in the forbidden band thus originating different colors emission. One of the most versatile methods to synthesize ZnO nanoparticles with specific defects is the pulsed laser ablation in liquid (PLAL); the ablation conditions that determine the end product are indeed dependent both on laser and liquid parameters. In this work, we used two pulsed laser sources, ns Nd:YAG (1064 nm) and fs Ti:Sapphire (800 nm), to irradiate a Zn target immersed in water, by which ZnO wurtzite nanocrystals result from the Zn oxidation [1]. Photoluminescence was investigated by time-resolved spectra acquired under a tunable laser excitation. We observed three PL bands that are excited by band-to-band transition: the first, peaked at 3.3 eV and decaying in a sub-ns timescale, is due to the excitonic recombination; the second, centered at 2.3 eV and decaying in µs-ms, is associated with oxygen vacancies [2]; the third, centered at 2.8 eV and decaying in ns, is peculiar to ZnO produced by fs PLAL, its origin being unclear yet. These results are promising in view to the realization of multi-color ZnO nanosystems thus increasing their application in lighting technologies

References

[2] P. Camarda, F. Messina, L. Vaccaro, S. Agnello, G. Buscarino, R. Schneider, R. Popescu, D. Gerthsen, R. Lorenzi, F. M. Gelardi, and M. Cannas, Phys. Chem. Chem. Phys., 18 (2016) 16237.