Synthesis and up-conversion emissions of Yb$^{3+}$/Er$^{3+}, Yb$^{3+}$/Tm$^{3+}$ and Yb$^{3+}$/Tm$^{3+}$/Gd$^{3+}$ co-doped KLu$_2$F$_7$

[摘要] Yb$^{3+}$/Er$^{3+}$, Yb$^{3+}$/Tm$^{3+}$, or Yb$^{3+}$/Tm$^{3+}$/Gd$^{3+}$ co-doped KLu$_2$F$_7$ up-conversion (UC) materials were synthesizedthrough a hydrothermal method or an additive-assisted hydrothermal method. The X-ray diffraction (XRD) resultssuggested that the materials crystallized in orthorhombic phase, yet, the potassium citrate (CitK) introduction affectedimmensely the crystalline purity of final material. The field emission scanning electron microscopy (FE-SEM) results suggestedthat the additive adding had effects on size and morphology of the material, which affected the UC emissions further. Green/red UC emissions of Er$^{3+}$, UV/blue/IR UC emissions of Tm$^{3+}$, and UV UC emissions of Gd$^{3+}$ were observed in the orthorhombic phase of KLu$_2$F$_7$ materials. The excitation power-dependent UC emissions illustrated that the UC emissionintensity initially increased, then decreased with the increase in excitation power. At the same time, the variation ratesof different transitions in Er$^{3+}$ or Tm$^{3+}$ are also different. In addition, the Er$*{3+} or Tm$^{3+}$ concentration-dependent UC emission results suggested that the optimal doping concentration of Er$^{3+}$ is 2 mol% and Tm$^{3+}$ is 0.5 mol% with the Yb$^{3+}$ concentration fixed as 20 mol%. The experimental results suggest that the orthorhombic phase of KLu$_2$F$_7$ should be a good host lattice for UC emitters.

[学科分类] 材料工程

[关键词] Hydrothermal synthesis;up-conversion;optical properties;rare earth.