Enhancing upconversion emission of Er3+ in single β-NaYF4 microrod through constructing different inert and active shells with doping Yb3+ ions

Abstract The construction of core-shell structure helps in enhancing upconversion luminescence in lanthanide-doped micro/nanomaterials. This study aimed to synthesize a series of NaYF4 and NaErF4 core-shell microrods based on epitaxial growth technology so as to enhance the upconversion emission. The upconversion luminescence properties of single NaYF4:Yb3+/Er3+ and NaErF4 microrods with different core-shell structures were carefully studied using a confocal microscope spectroscopy test system under 980-nm near-infrared excitation. The upconversion emission intensity and red-to-green emission intensity ratio of Er3+ ions were remarkably enhanced in different single microrods by building different inert and active core-shell structures. The higher red-to-green ratio was mainly due to the cross-relaxation between Er3+ ions and the energy back-transfer process from Er3+ to Yb3+ ions, which were explained on the basis of spectral characteristics and rate equations. These tunable NaYF4 and NaErF4 core-shell microrods had the potential to be applied to displays, micro-lasers, and anti-counterfeiting.