Self-modification of spontaneous emission by inverse opal silica photonic crystals

Modification of the photoluminescence emission of sol-gel-derived silica by three-dimensional photonic crystal effects is reported. Three-dimensionally ordered macroporous (3DOM) silica inverse opal materials prepared by polystyrene colloidal crystal templating, using the sol-gel method, exhibit broadband blue emission under UV excitation. 3DOM silica materials also possess a photonic stop band in the visible range of their optical spectra, with a controllable position dependent on several factors, including the macropore size, wall thickness, and refractive index contrast between the walls and the void-filling material. Tuning the photonic stop band of 3DOM silica to overlap with the photoluminescence emission band leads to competitive Bragg diffraction and electronic emission processes, resulting in a modified emission spectrum with a depression correlating with the spectral position of the stop band. Solvent-filling of the 3DOM silica changes the refractive index contrast and shifts the photonic stop band out of the spectral range of the photoluminescence emission band, restoring the broadband emission spectrum typical of sol-gel-derived silica. Grinding the 3DOM silica destroys the photonic crystal order, also restoring the broadband emission.