A review on rare-earth activated SnO2-based photonic structures: Synthesis, fabrication and photoluminescence properties

Rare-earth-activated photonic structures are fundamental actors in widespread applications such as luminescence sources, lasers, integrated photonics, solar cells, biomedical sensors and imaging, biomarkers, and theragnostics. However, there are several critical problems to face, concerning the quantum yield of the rare-earth (RE) based photonic systems such as: low absorption cross-section of rare-earths, physical and chemical clusterings, and non-radiative relaxation processes. Exploiting semiconductors as RE host-sensitizers is among appealing approaches to overcome these matters. By incorporating rare-earth ions in semiconductor nanocrystals, several advantages concerning the quantum yield of the systems can be achieved: (i) high absorption and emission cross-sections, (ii) reduction of the non-radiative relaxation processes, and (iii) tailoring of the ion-ion interaction by the control of the rare-earth ion partition. In this review paper, a survey on the investigation of SnO nanocrystals, a wide bandgap semiconductor, as luminescence sensitizers for a range of rare-earth ions such as erbium (Er), europium (Eu), samarium (Sm), terbium (Tb), holmium (Ho), neodymium (Nd), and ytterbium (Yb) is provided. Photoluminescence measurements of various rare-earth-doped SnO thin films or nanoparticles, and SiO-SnO glass-ceramic systems are presented to put in evidence the role of SnO nanocrystals as efficient REs sensitizers. Synthesis and fabrication methods to obtain the rare-earth activated SnO-based photonic structures are also summarized.