Silica aerogels were patterned with CdS using a photolithographic technique based on local heating with infrared (IR) light. The solvent of silica hydrogels was exchanged with an aqueous solution of the precursors CdNO3 and NH4OH, all precooled to a temperature of 5°C. Half of the bathing solution was then replaced by a thiourea solution. After thiourea diffused into the hydrogels, the samples were exposed to a focused IR beam from a continuous wave, Nd-YAG laser. The precursors reacted in the spots heated by the IR beam to form CdS nanoparticles. We lithographed features with a diameter of about 40μm, which extended inside the monoliths for up to 4mm. Samples were characterized with transmission electron microscopy and optical absorption, photoluminescence, and Raman spectroscopies. Spots illuminated by the IR beam were made up by CdS nanoparticles dispersed in a silica matrix. The CdS nanoparticles had a diameter in the 4–6nm range in samples exposed for 4min to the IR beam, and of up to 100nm in samples exposed for 10min.

Highly luminescent semiconductor quantum dots have been synthesized in porous materials with ultraviolet and x-ray lithography. For this, the pore-filling solvent of silica hydrogels is exchanged with an aqueous solution of a group II metal ion together with a chalcogenide precursor such as 2-mercaptoethanol, thioacetamide or selenourea. The chalcogenide precursor is photodissociated in the exposed regions, yielding metal chalcogenide nanoparticles. Patterns are obtained by using masks appropriate to the type of radiation employed. The mean size of the quantum dots is controlled by adding capping agents such as citrate or thioglycerol to the precursor solution, and the quantum yield of the composites can be increased to up to about 30% by photoactivation. Our technique is water-based, uses readily available reagents, and highly luminescent patterned composites are obtained in a few simple processing steps. Polydispersity, however, is high (around 50%), preventing large-scale usage of the technique for the time being. Future developments that aim at a reduction of the polydispersity are presented.

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