Synthesis and upconversion luminescence in highly crystalline YOF:Yb3+/Er3+ and Yb3+/Tm3+ microboxes

► YOF:Ln3+ microboxes were successfully synthesized for the first time. ► The mixed NaNO3–KNO3 flux cooling method was adopted. ► Multicolor UC emissions of YOF:Yb3+/Er3+ microboxes can be achieved. ► The intense NIR emission in YOF:Yb3+/Tm3+ microboxes is obtained. Highly crystalline YOF:Ln3+ (Ln=Yb, Er, Tm) microboxes were successfully synthesized for the first time by using a mixed NaNO3–KNO3 flux cooling method at a holding temperature of 600°C for 2h in air. The results indicated that the as-obtained products belonged to tetragonal system and exhibited microboxes morphology with side lengths of 0.5–2μm. The upconversion luminescence properties of as-prepared YOF:Yb3+/Er3+ and YOF:Yb3+/Tm3+ were investigated in detail. Under 980nm laser diode (LD) excitation, the emission intensity and the corresponding luminescence colors of YOF:Yb3+/Er3+ and YOF:Yb3+/Tm3+ could be precisely adjusted by changing the doping concentration of Yb3+ ions. Furthermore, the paper also offers a new alternative in synthesizing such materials and opens the possibility to meet the increasing commercial demand.