Preparation And Characterization Of CdS-SiO₂ Photonic Crystals

Photonic crystals have received considerable attention due to their capabilities to confine and to control elecreomagnetic waves in the nano-space and femtosecond time scale and come to being a novel and promising field in materials science. A photonic crystals is a dimensionally ordered dielectric materical or structure having a spatial periodic dielectric constant with a lattice parameter comparable to the wavelength of the electromagnetic wave. Under suitable conditions, a photonic crystal with complete band gap can be used to localize electromagnetic waves to specific areas, to inhibit or to inhance spontaneous emission, and to guide propagation of electromagnetic waves along certain directions at restricted frequencies. Because of these properties, photonic crystals have pontential practical applications. It made the photoelectronic technic entry to a new developing stage, although it be studied in the laboratory at the present time.SiO₂ is the most widely used material for photonic crystals assembly, but the colloidal photonic crystals assembled by SiO₂ do not have complete band gap. When it be filled with materials which have high dielectric constant among the intersphere cavity network , this can lead to the formation of broad or a full photonic band gap. In this work, we used the method of vertical deposition to produce SiO₂ colloidal photonic crystal with highly quality under different conditions, infilled it with CdS nano-scale particles by multiple-dip CBD. The optical properties of the prepared photonic crystal were studied by SEM , UV-VIS-N1R spectrograph and spectrofluorimeter. The following conclusions are obtained:(1) The environment conditions influent the quality of SiO₂ colloidal photonic crystal very much. For the colloidal particles of 353-400nm in diameter, the high-quality SiO₂ colloidal photonic crystals were obtained at the environment temperature between 45℃ and 55℃, humidity between 66% and 76% , when the volume fraction of micro-sphere is between 0.8% and 1.5%, and it had the photonic bandgap in the near infrared band.(2) It was found that the quality of CBD-CdS films was dependent on the NH₃ concentration. Higher NH₃ concentration led to the formation of the incoherent and unfastened film, and higher S^2- and Cd²⁺ concentration tend to increase the size of CdS particles, but increasing S^2- and Cd²⁺concentration ratio ([S2"]/[Cd2+]) decreased the size of CdS particles under the same NH3 concentration.(3) Increasing the amount of the infilled CdS particles will cause the photonic band gap to move to long-wavelength and to be broadened. The photoluminescence test showed that the luminescence peak also moved to long-wavelength while the amount of the infilled CdS particles was increased.(4) PL characters of the CdS can be adjusted by controlling the size of the SiO2 colloidal particles.