The present invention relates to a transmitter for transmitting data and for emitting electromagnetic radiation in the visible spectral range, wherein the transmitter comprises a) a radiation source for generating and emitting first electromagnetic radiation, b) a modulator being adapted to modulate the first electromagnetic radiation depending on the data to be transmitted generating modulated first electromagnetic radiation, and c) a frequency converter for converting at least a part of the modulated first electromagnetic radiation into modulated second electromagnetic radiation, said modulated second electromagnetic radiation being different from the modulated first electromagnetic radiation, wherein the frequency converter comprises a polymeric matrix material comprising at least one organic fluorescent colorant. Furthermore, the invention relates to an illumination device comprising such transmitter. Moreover, the invention relates to a data transmission system comprising such a transmitter as well as a receiver and a data analyzer.