SiAlON window coatings are applied on an industrial scale to achieve e.g. scratch-resistance and anti-reflection. Doping these SiAlONs with rare-earths adds luminescent functionality, which could be applied in photovoltaics. By using a combinatorial reactive sputtering approach, an amorphous thin film composition library with a Si:Al ratio from 0.062:1 to 3.375:1 and a Eu doping from 4.8 at% to 26 at% is created. This library uniquely combines high absorption, strong emission and absence of light scattering. By combining position-dependent EDX measurements with transmission and emission spectra, properties like the index of refraction, absorption strength, emission wavelength and decay times of the library can directly be related to the composition. Throughout the library, an index of refraction of 1.63±0.03 is observed, typical for a film with low nitrogen content. The library also shows a large absorption coefficient of 1294±8cm−1at.%−1. Laser-excited emission spectra show that the library has a strong redshift from 500 nm to 550 nm with increasing Al concentration. An increase in Eu concentration also causes a shift of the emission to red. Decay spectra show that a high degree of Si greatly improves the luminescence intensity. These functionalized SiAlON coatings can be of great interest for transparent and scatter-free luminescent solar concentrators applied as windows.@en