We thank EPSRC for financial support from the UP-VLC Project Grant (EP/K00042X/1). I.D.W.S. and P.J.S. are Royal Society Wolfson Research Merit Award holders. For white light data communications, broad-band light emitting materials are required, whose emission can be rapidly modulated in intensity. We report the synthesis, photophysics and application of a novel semiconducting polymer for use as a high bandwidth colour converter, to replace commercial phosphors in white LEDs. The high modulation bandwidth (470 MHz) is 140 times higher than that measured using a conventional LED phosphor. Publisher PDF