Fast synthesis of β-NaYF4:Ln3+ (Ln = Yb/Er, Yb/Tm) upconversion nanocrystals via a topotactic transformation route

Monodisperse beta-NaYF4:Ln(3+) (Ln = Yb/Er, Yb/Tm) upconversion nanocrystals have been fast synthesized using layered yttrium hydroxide Y-2(OH)(5)NO3 center dot nH(2)O (LYH) via a topotactic transformation route bypassing the alpha-NaYF4 intermediate phase. It was found that the topotactic structural matching of [001] LYH//[0001] beta-NaYF4 facilitated the direct formation of beta-NaYF4, wherein the kinetic alpha-NaYF4 intermediate phase could be avoided at the initial reaction stage. Besides, the morphology could be effectively tuned by manipulating the NaF/Y(NO3)(3) feeding ratio. In addition, the upconversion luminescence properties of the as-prepared beta-NaYF4: 15% Yb3+/2% Er3+ and beta-NaYF4:15% Yb3+/1% Tm3+ were also systematically investigated.