We report a facile sol-gel synthesis of colloidally stable Fe₂O₃ and ZnO nanoparticles in alcoholic solvents, ROH, where R = methyl, ethyl, n-propyl, isopropyl, and tert-butyl. We show that nanoparticles of ZnO (4-42) nm and Fe₂O₃ (4-38 nm) monotonically increase in size upon increasing the alkyl chain length and branching of the alcohol solvent.

These colloidally stable and size-controllable metal oxide nanoparticles enable the formation of high optical quality films and photonic crystal multilayers whose component layer thickness, refractive index, porosity, and surface area are found to scale with the nature of the alcohol.

Utility of these colloidally stable nanoparticles is demonstrated by preparation of one-dimensional porous photonic crystals comprising ncZnO/ncWO₃ and ncFe₂O₃/ncWO₃ multilayers whose photonic stop band can be tuned by tailoring nanoparticle size. Myriad applications can be envisaged for these nanoparticle films in, for example, heterogeneous catalysis, photocatalysis, electrocatalysis, chemical sensors, and solar cells. 

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