Synthesis and upconversion properties of KAlF4:Yb3+/Er3+ phosphor for bioimaging application

This article reports a simple and green synthesis route for the preparation of Er3+/Yb3+-co doped KAlF4 upconversion phosphor. When annealed at 450 ?C, the crystalline phase of KAlF4 host changes from monoclinic to tetragonal. Upon 980 nm light irradiation, KAlF4: Er3+ phosphor shows two emission bands centred at 662 nm (F-4(9/2) -> I-4(15/2)) and 834 nm (S-4(3/2) -> I-4(13/2))respectively, in which the red emission band corresponds to the intra-4f transitions of Er3+ ions and hence the upconversion luminescence mechanism observed due to the two-photon process. With co-doping of Yb3+ ions, upconversion luminescence in KAlF4: Er3+ phosphor enhanced to few extend and exhibit two strong emission band appears invisible spectral range that consists of strong red emission band and two high-moderate green emission band. As a result, Er3+/Yb3+ co-doped KAlF4, laser-light excited upconversion phosphor may be an excellent candidate for bioimaging applications.