Synthesis and Characterization of Luminescent Nanostructured SiOC Thin Films

A new approach to obtain visible luminescence from sol-gel derived SiOC films is proposed. This novel method is based on a simple processing route to produce nanostructured multicomponent ceramics. According to this route, hybrid sol-gel derived precursors are converted to ceramic materials by a pyrolysis process in controlled atmosphere at 800-1000°C. Higher temperatures lead to formation of Si-rich SiOC, C-rich SiOC or stoichiometric SiOC according to the starting composition. The final composition, which is relevant to line emission, can be easily controlled through a number of processing parameters like the composition of the preceramic gel and the heat treatment conditions. Thus, this new processing method seems very well suited for the production of white emitting materials since the Si- and C-based emission can be tuned across the visible spectral range from UV-blue to red by controlling film composition. A further advantage of this method is that the thin films can be formed on Si or quartz wafers and this can serve as starting material to process more complex photonic devices such as waveguides or LEDs. In the amorphous state (800-100°C), all SiOC films showed UV-blue luminescence peaking at about 410 nm, which is attributed to defect states present in the matrix such as dangling bonds. The increase of the pyrolysis temperature (≥1100°C) led to the partition of SiOC and formation of SiC, C and Si phases. The intense green-yellow luminescence observed in stoichiometric SiOC films caused by the presence of SiC and very low amount of free C. On the other hand, Si rich SiOC film showed a very broad and extremely intense white luminescence peak centred at 620 nm covering almost all visible range (430 nm-900 nm) at 1200 °C. This behaviour is explained by the simultaneous presence of SiC, C and Si in the film. External quantum efficiency measurements yielded 11.5% and 5% efficiencies in Si rich SiOC and stoichiometric SiOC films, respectively, pyrolysed at 1200°C. On the other hand, C rich SiOC films did not show any noticeable improvement in PL, indicating that C excess in the SiOC system is detrimental for the luminescence behaviour. Solutions which used in thin film production have been characterized extensively by means of several characterization properties. Moreover, the related powders and bulks have been characterized for the sake of coherency and widen the study. In addition, a study on volumetric shrinkage of films and powders has been done. The results showed that the shrinkage in films happens almost 200°C earlier than powder and higher amount of siloxane release due to the low dimension, the shrinkage is higher than powders. The last part of the study dedicated to two different systems, SiBOCs and SiOCNs, in order to understand the effect of the boron addition on SiOC system and study the optical properties of the SiOCN. Tunable (color emission change) SiOC films is obtained with high quantum efficiency by adding very few amount of boron in SiOC. Moreover, the processing temperature is decreased and very broad emission is obtained. Finally, results showed that SiOCN PDC gives very high emission in UV range and they are promising materials for UV-LEDs