Strength and weakness of rare earths based phosphors: Strategies to replace critical raw materials

Rare earth based phosphors are largely the most applied luminescent materials in the present lightening devices. Their ubiquity in lighting system, like light emitting diodes or compact fluorescent lamps, is related to the optical high efficiency of the rare earth as luminescent ions but also to the relative easiness of growth technique as well high structural stability of rare earth based host matrices, like garnets, perovskites and oxyorthosilicatas. On the other hand, the need of new devices virtually free of any elements with high supply disruption, the ones classified by EU community and US government as critical raw materials, boosts the research for alternatives materials. In this paper, we focalize on the optical properties of the REE based phosphors with the intent to underline the performances the new materials should grant, thus addressing the possible direction for new material development. In particular the features related to the possibility of tuning the luminescence, the interaction among doping ions and with surface defects were analysed. Finally, a general model to predict the role of the REE in a host matrix is analysed.