Tunable multicolor and bright white emission of one-dimensional NaLuF4:Yb3+,Ln3+ (Ln = Er, Tm, Ho, Er/Tm, Tm/Ho) microstructures

Abstract

Well-defined one-dimensional NaLuF₄:Yb³⁺,Er³⁺/Tm³⁺/Ho³⁺ microtubes and microrods were successfully prepared by a surfactant-free molten salt method for the first time. It is found that with the prolonged time, the phase of NaLuF₄ transforms from cubic to hexagonal, while the morphology changes from nanoparticles to microtubes then to microrods. Moreover, upon 980 nm laser diode (LD) excitation, white up-conversion (UC) light was successfully achieved by properly tuning the sensitizer (Yb³⁺) concentration in the host matrix. The relative emission intensities of different emission colors in Yb³⁺/Er³⁺, Yb³⁺/Tm³⁺, and Yb³⁺/Ho³⁺ doped β-NaLuF₄ can be precisely adjusted in a broad range by tuning the Yb³⁺ doping concentration. Consequently, effective UC emissions with multicolors and a strong white light can be realized in β-NaLuF₄:Yb³⁺/Er³⁺/Tm³⁺, and β-NaLuF₄:Yb³⁺/Tm³⁺/Ho³⁺ structures by the appropriate control of the emission intensity balance for the three blue, green, and red basic colors. UC mechanisms in the co-doping and tri-doping β-NaLuF₄ samples were analyzed in detail based on the emission spectra and the plot of luminescence intensity to pump power. The as-obtained abundant luminescence colors in a much wide region contribute themselves great potential applications in various fields. Furthermore, the paper also provides an effective and facile approach to gain a desired color by manipulating the sensitizer concentration.