Towards white luminophores: Developing luminescent silica on the nanoscale

Nanoscale luminescent probes are useful in a number of applications, from optics to biomedicine. The phenomenon of bulk luminescent silica which emits in the UV-visible range prepared without the use of a metallorganic emitter or organic dye host is prevalent in the literature, although the mechanism of luminescence is still a source of controversy. Nanomaterials displaying similar intrinsic or defect emission would be highly advantageous, particularly as imaging probes. The preparation of nano-sized emitters of this type is less well documented however, mainly due to the challenges of translating bulk preparative procedures to the nanoscale. In this work we report the preparation of silica nanowires and nanoparticles based on the aqueous sol-gel technique which display broad white emission in the visible range of the spectrum without the need for traditional dyes. The source of emission is from the formation of hydrocarbon-based defects during synthesis. We also describe for the first time white-light emitting silica nanoparticles prepared by the Stöber technique.