Fast synthesis of β-NaYF4:Ln3+ (Ln = Yb/Er, Yb/Tm) upconversion nanocrystals via a topotactic transformation route
Abstract
Monodisperse β-NaYF4:Ln3+ (Ln = Yb/Er, Yb/Tm) upconversion nanocrystals have been fast synthesized using layered yttrium hydroxide Y2(OH)5NO3·nH2O (LYH) via a topotactic transformation route bypassing the α-NaYF4 intermediate phase. It was found that the topotactic structural matching of [001]LYH//[0001]β-NaYF4 facilitated the direct formation of β-NaYF4, wherein the kinetic α-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 β-NaYF4:15%Yb3+/2%Er3+ and β-NaYF4:15%Yb3+/1%Tm3+ were also systematically investigated.