Although phosphor-coated white light LEDs have become the mainstream for bright illumination the colour-conversion phosphors used in the mix have largely varying photoluminescence lifetimes. As an example, inspecting the time-resolved yellow emission photoluminescence spectra of a white LED at 450 and 560nm, the researchers revealed a decay time for blue light emission of 1.4ns, much faster than the 54.4ns for the yellow light emission.
This means that when a white-light is modulated to transmit a digital signal, the blue light effectively turns on and off at a faster rate than the yellow phosphor emission, and a broadband Si photodetector ends up getting the slowest common denominator of the signal, slow rise and fall times.
To focus on the fast blue emission, the researchers devised a narrowband, green InGaN LED as the receiver. Their paper "Textured V‑Pit Green Light Emitting Diode as a Wavelength-Selective Photodetector for Fast Phosphor-Based White Light Modulation" published in the ACS Photonics journal details the fabrication of an InGaN LED with a sharp wavelength selectivity at 380nm, using V-pit texturing to improve the peak responsivity of the thin active layer in the InGaN LED.