Large-scale synthesis of highly pure novel cadmium semi-spheres and their anomalous optical properties

Highly pure and large-scale novel cadmium (Cd) semi-spheres were prepared via Chemical Vapor Deposition (CVD). The growth process is described with multi-steps of Vapor-Liquid-Solid (VLS) and decomposition of CdS nanostructure in Ar(90%)+H₂ (10%) mixture gas stream at definite temperature and selected zone. In contrast to previous Cd nanostructures, our individual Cd semi-spheres show strong room-temperature photoluminescence (PL) at around 591nm, which is detected for the first time. Its long lived (>~1.5ns) electronic state by time-resolved PL supports the origin of strong emission, which is attributed to radiative recombination of electrons in the s, p conduction band near the Fermi surface and the holes at the d-bands or local microstructures generated by UV-visible laser excitation. It is a plasmonic band as that in Au, Ag, Cu tuned by sizes. Strong surface enhanced Raman scattering (SERS) of pyridine species have been detected from this Cd semi-sphere, as strong as the silver metals does for SERS agents. The above optical responses has strong relation to their growth process and as formed microstructures in one sphere. It reflects that such Cd spheres may be a much cheaper candidates for applications in LEDs and other optoelectronic devices, for example, the plasmonic enhanced solar cells.