Influence of surfactants on the morphology, upconversion emission, and magnetic properties of β-NaGdF4:Yb3+,Ln3+ (Ln = Er, Tm, Ho)

In this article, rare earth (RE) ion doped β-NaGdF4 crystals with multicolor up-conversion (UC) emissions and paramagnetic properties were synthesized via a simple one-step precipitation method at room-temperature for the first time. Different surfactants, including Na2EDTA, PVP, SDS, and Na2tar, were introduced to control the crystal size and morphology. It was found that the organic additive can strongly control the size and structure of as-prepared β-NaGdF4:Yb(3+),Ln(3+) samples through absorbing on the surface of primary particles and/or coordinating with RE(3+) ions. Most interestingly, the UC and magnetic properties of the NaGdF4 crystals were also greatly influenced by those additives, which exhibit great distinction. The red emission of (4)F(9/2)→(4)I(15/2) (655 nm) in β-NaGdF4:20%Yb(3+),2%Er(3+), (5)F5→(5)I8 (648 nm) in β-NaGdF4:20%Yb(3+),2%Ho(3+), and NIR emission of (3)H4→(3)H6 (797 nm) in β-NaGdF4:20%Yb(3+),2%Tm(3+) were all markedly enhanced due to abundant organic groups that affect the nonradiative processes. The magnetic properties of β-NaGdF4:Yb(3+),Er(3+) crystals prepared with different surfactants exhibit typical paramagnetic behavior with different intensities due to the different crystal shape anisotropy.