Efficient transparent light converters have received lately a growing interest from optical device industries (LEDs, PV,
etc.). While organic luminescent dyes were tested in PV light-converting application, such restrictions as small Stokes
shifts, short lifetimes, and relatively high costs must yet be overcome. Alternatively, use of phosphors in transparent
matrix materials would mean a major breakthrough for this technology, as phosphors exhibit long-term stability and are
widely available. For the fabrication of phosphor-filled layers tailored specifically for the desired application, it is of
great importance to gain deep understanding of light propagation through the layers, including the detailed optical
interplay between the phosphor particles and the matrix material. Our measurements show that absorption and
luminescent behavior of the phosphors and especially the scattering of light by the phosphor particles play an important
role. In this contribution we have investigated refractive index difference between transparent binder and phosphors.
Commercially available highly luminescent UV and near-UV absorbing μm-sized powder is chosen for the fabrication of
phosphor-filled layers with varied refractive index of transparent polymer matrix, and well-defined particle size
distributions. Solution-processed thick layers on glass substrates are optically analyzed and compared with simulation
results acquired from CROWM, a combined wave optics/ray optics home-built software. The results demonstrate the
inter-dependence of the layer parameters, prove the importance of careful optimization steps required for fabrication of
efficient light converting layers, and, thus, show a path into the future of this promising approach.