Shape-controllable synthesis and enhanced upconversion luminescence of Li+ doped β-NaLuF4:Yb3+,Ln3+ (Ln = Tm, Ho) microcrystals

The applications of upconversion (UC) materials are still restricted due to their low upconversion luminescence efficiency. In this work, beta-NaLuF4 microcrystals microcrystals with different morphologies and Li+ doped beta-NaLuF4:Yb3+,Ln(3+) (Ln = Tm, Ho) microcrystals were synthesized by a hydrothermal method using citric acid as a chelating agent. Hexagonal microtubes, hexagonal microprisms with scrappy ends, hexagonal microprisms, and hexagonal microdisks were obtained by simply adding different amounts of NaOH in the initial reaction solution. Li+ doped beta-NaLuF4:Yb3+,Ln(3+) (Ln = Tm, Ho) microcrystals were successfully prepared for the first time. Compared to their Li+-free counterpart, upconversion luminescence intensities of blue emission (477 nm) in beta-NaLuF4:Yb3+,Tm3+ microcrystals doped with 15 mol% Li+ are enhanced by 6 times, green emission (538 nm) and red emission (644 nm) in beta-NaLuF4:Yb3+,Ho3+ microcrystals doped with 15 mol% Li+ are enhanced by 7 and 3 times, respectively. The effect of Li+ on the enhancement of upconversion emission intensity is discussed systematically. The results suggest that the enhanced upconversion luminescence intensity of Li+ doped beta-NaLuF4:Yb3+,Ln(3+) (Ln = Tm, Ho) microcrystals may have potential applications in optoelectronic devices such as photovoltaic and plasma display panel devices.