Colloids and Quantum Dots

Indirect band-gap materials exhibit no significant photoluminescence (PL) at room temperature. As a specific nano-effect the quantum confinement in semiconductor clusters induces visible room-temperature PL. Thus, nano-colloidal silicon, molybdenum sulfide, and pyrite shows intense luminescence. 

The famous quantum dots are nanometer-size colloidal particles smaller than the exciton radius. These quantum dot materials are around 20 times brighter and more than 100 times more stable against photo-bleaching compared to organic fluorescent dyes. Within recent years these luminescent nano-particles found wide-spread use for multicolor staining, homogenous assays, and tissues imaging. 

Colloidal gold is orange, red, or red-violet, depending on the preparation method and thus on size and aggregation state. Orange indicates the lack of a plasmon band and is a direct indicator of ultra-small gold colloids up to a few nm in size. A red gold sol 

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