Synthesis And Luminescence Properties Of KY₃F₁₀ Nanocrystals

Fluoride nanocrystals are vital inorganic luminescent materials and have great application potential in biology, therapy and LED. For example, Er3+:Yb3+:NaYF4 nanocrystasls are efficient up-converted luminescent biomaterials while Mn4+:Na2SiF6 nanocrystasls are novel red-emitting phosphors. The emission mechanisms of luminescent materials include emisisons from luminescent activator ions, from semicondoctors, from ceoss luminescence and from defects and so on, in which defect emission exists in some fluorides. Defect-related luminescent materials have features such as low toxicity, stability, tunable emission color and low cost. Yet the efficiency of it is frequently low, and the understanding of its mechanism is limited either. Consequently more in-depth insight needs to be given into these materials. Based on KY3F10 nanocrystals, the mechanism of defect emission and the luminescence properties of rare earth ions were investigated in this work.Undoped and a series of rare earth doped KY3F10 nanocrystals were synthesized by hydrothermal technique with citric acid as the chelator. SEM images indicate that excess chelator results in particle agglomeration. Under 300 nm excitation, undoped KY3F10 nanocrystals exhibit UV-blue broadband emission originated from defects. The strongest defect luminescence with internal quantum efficiency of 23.73% is obtained when the chelator consumption is half that of rare earth, which is easily seen with the naked eye. The emission of Ce3+ in KY3F10 has additive effect on defect emission After doping 1 mol% Ce3+, a fivefold enhancement is observed in the broadband emission. And the strongest emission is obtained from the sample with 6 mol% Ce3+ content. Yet minute quantities of Lu3+ions introduced significantly weaken the emission of 0.06Ce3+:KY3F10.0.02Gd3+:KY3F10 nanocrystals exhibit UV-blue and narrow band UVB emissions at 313 nm under 300 and 273 nm excitation, respectively, indicating they’re UVA/UVB dual wavelength phosphors. Due to the combinative effect of defect luminescence, cross relaxation and energy transfer, warm white emission is obtained form either Tb3+/Sm3+single doped or codoped samples. By switching the doping content or excitation wavelength, multi-color luminescence including blue, green, yellowish green, yellowish orange, reddish orange and pink can be achieved from Tb3+/Sm3+ doped KY3F10. Due to the existence of energy level of defect luminescence, dual color emission of cold white, pink and orange, orange-red, respectively, was observed in 0.02Pr3+:KY3F10 and 0.02Eu3+:KY3F10, making them effective dual color phosphors.