Investigation of Remote-Phosphor White Light-Emitting Diodes with Multi-Phosphor Layers

To understand how multiple phosphors in a mixture or stacked layers affect the performance of the remote-phosphor "scattered photon extraction (SPE)" white light-emitting diode (LED), a laboratory study was conducted with commercial yellow [quantum efficiency (QE)=0.91] and red (QE=0.59) phosphors in equal amounts. The highest light output was obtained when the longer-wavelength red phosphor was placed as the second layer. Experiments showed that when using two phosphors in an SPE package, several factors influence the performance: mixture or stacked layers; specific layer order; phosphor densities; phosphor external QE; overall spectral power distribution (SPD); phosphor excitation and emission spectra and efficiencies.