Yb3+/Er3+ codoped β-NaYF4 microrods: Synthesis and tuning of multicolor upconversion

A series of β-NaYF4 microrods doped with Yb3+/Er3+ have been successfully synthesized through a facile hydrothermal method. The fluoride microcrystals have been characterized by XRD, SEM, and the photoluminescence spectra method. The upconversion spectra show that the output light color have been tuned from green to red under near infrared excitation at 977 nm when replacing Y3+ ions with a different amount of Yb3+ in NaYF4:Yb/Er microcrystals. The effect of the intrinsic structural feature of fluoride compounds and four external factors, namely the concentration of Yb3+, the concentration of Er3+, the particle size and the use of an organic additive (EDTA), on the ultimate output light color of samples are investigated detailedly. The results show that the output light color is more sensitive to the concentration of Yb3+ than that of Er3+. When elevated the concentration of dopants (Er3+ or Yb3+) in the NaYF4 host lattice, the cross-relaxation process derived from Er3+ promoted the red emission and quenched the green emission.

► The dependence of size on ionic radius is attributed to the change on growth rate.
► The luminescence emission can be deliberately tuned from visible to NIR.
► The value of n sharply decreases with the Yb3+ concentration increase.
► When elevating dopant-concentration, the cross-relaxation from Er3+ is rampant.