Upconversion emissions in YAG glass ceramics doped with Tm3+/Yb3+ ions

► YAG micro-crystals present primary and secondary particle sizes of ∼46 nm and ∼8 μm. ► Crystal grains grow with several preferred orientations and a dominant one (4 4 4). ► Efficient NIR, weak red, intense blue and rare UV emissions of Tm3+ are captured. ► Obvious Stark splitting in the levels of Tm3+ is confirmed in the glass ceramics.