Contents: (Adv. Sci. 12/2016)

Wavelength-tuneable single-band upconversion (UC) can be achieved in some transition metal ion (TMI) activated systems ascribed to the susceptibility of d-electrons to the chemical environment. Moreover, UC of lanthanide ions (Ln3+) can be modulated by TMI, which benefits from the specific metastable energy levels of Ln3+ owing to the well-shielded 4f-electrons and tuneable energy levels of TMI. The combination also brings out additional functions like antiferromagnetism, ferroelectricity, and oxide-ion conductivity as well. Recent advances in this research field are reviewed in article 1600302 by Shi Ye, En-Hai Song, and Qin-Yuan Zhang.