Highly uniform microbeads containing a single fluorescence dye or a mixture of fluorescence dyes, which can be excited over a wide range of the spectrum extending from the ultraviolet to the infrared, and which can be used to align a flow cytometer or fluorescence microscope....http://www.google.de/patents/US5073498?utm_source=gb-gplus-sharePatent US5073498 - Fluorescent alignment microbeads with broad excitation and emission spectra and its use
