Rapid microwave-assisted flux growth of pure β-NaYF4:Yb3+, Ln3+ (Ln = Er, Tm, Ho) microrods with multicolor upconversion luminescence

•β-NaYF4 microrods were successfully synthesized within only 12 min.•A rapid microwave-assisted flux cooling method was adopted.•Phase and morphology evolution process as well as formation mechanism were discussed.•Multicolor (yellow, blue, green) upconversion emissions can be obtained.

Pure hexagonal β-NaYF4:Yb3+, Ln3+ (Ln = Er, Tm, Ho) microrods were successfully synthesized for the first time through a rapid microwave-assisted flux cooling method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra were used to characterize the samples. The results indicate that with the prolonged time, the phase of product transforms from orthorhombic YF3 to hexagonal NaYF4, while the morphology changes from nanoparticles to hollow microtubes then to solid microrods. The microwave (MW) heating technique allows for a reduction of about 90% in preparation time, making it possible to obtain pure β-NaYF4 microrods within only 12 min. By changing the dopant’s species, multicolor (yellow, blue, and green) upconversion (UC) emissions can be obtained in β-NaYF4:Yb3+, Ln3+ under 980 nm laser diode (LD) excitation. The UC mechanisms in Yb3+/Ln3+ co-doped β-NaYF4 samples were analyzed in detail based on the emission spectra and the plot of luminescence intensity to pump power. Importantly, this synthetic methodology may offer a new alternative in the preparation of high quality rare earth fluorides.

Graphical abstractA fast microwave-assisted flux cooling process was adopted for the preparation of well-defined β-NaYF4:Yb3+, Ln3+ (Ln = Er, Tm, Ho) microrods with multicolor upconversion luminescence.Figure optionsDownload full-size imageDownload as PowerPoint slide