Tb3+-Yb3+ co-doped SiNx down-conversion layers compatible with silicon Photovoltaic Technology were prepared by reactive magnetron co-sputtering. Efficient sensitization of Tb3+ ions through a SiNx host matrix and cooperative energy transfer between Tb3+ and Yb3+ ions were evidenced as driving mechanisms of the down-conversion process. In this paper, the film composition and microstructure are investigated alongside their optical properties, with the aim of maximizing the rare earth ions incorporation and emission efficiency. An optimized layer achieving the highest Yb3+ emission intensity was obtained by reactive magnetron co-sputtering in a nitride rich atmosphere for 1.2 W/cm(2) and 0.15 W/cm(2) power density applied on the Tb and Yb targets, respectively. It was determined that depositing at 200 degrees C and annealing at 850 degrees C lead to comparable Yb3+ emission intensity than depositing at 500 degrees C and annealing at 600 degrees C, which is promising for applications toward silicon solar cells. (C) 2015 Elsevier B.V. All rights reserved.