Preparation of NaYF4:Yb3+,Tm3+@NaGdF4:Ce3+,Eu3+ double-jacket microtubes for dual-mode fluorescent anti-counterfeiting

Novel hydrophilic NaYF 4 :Yb 3+ ,Tm 3+ @NaGdF 4 :Ce 3+ ,Eu 3+ double-jacket microtubes (DJMTs) with upconversion/ downconversion dual-mode luminescence were designed and prepared through epitaxial growth of NaGdF 4 :Ce 3+ , Eu 3+ shell onto the NaYF 4 :Yb 3+ ,Tm 3+ microtube via poly(acrylic acid) (PAA) mediated hydrothermal method. It is demonstrated that PAA ligand played an important role in guiding the direct growth of NaGdF 4 :Ce 3+ ,Eu 3+ shell onto the surface of NaYF 4 :Yb 3+ ,Tm 3+ parent microtubes. The growth of NaGdF 4 :Ce 3+ ,Eu 3+ shell experienced a crystal phase transition from β -NaGdF 4 and β -NaYF 4 mixture to β -NaYF 4 @NaGdF 4 composite crystal, and morphology evolution from mixture of β -NaGdF 4 :Ce 3+ ,Eu 3+ nanorods and β -NaYF 4 :Yb 3+ ,Tm 3+ microtubes to NaYF 4 :Yb 3+ ,Tm 3+ @NaGdF 4 : Ce 3+ ,Eu 3+ DJMTs. The formation mechanism of DJMTs was the dissolution−renucleation of β -NaGdF 4 :Ce 3+ ,Eu 3+ nanorods and the growth of β -NaGdF 4 :Ce 3+ ,Eu 3+ shell via the classical Ostwald ripening mechanism. The as-prepared DJMTs could exhibit blue upconversion and red downconversion luminescence, which was further made into environmentally benign luminescent inks for creating highly secured and fluorescent-based anti-counterfeiting patterns via inkjet printing.