Enhancement of red upconversion emission intensity of Ho3+ions in NaLuF4∶Yb3+/Ho3+/Ce3+@NaLuF4 core-shell nanoparticles

The red upconversion emission of Ho3+ions,in the optical window of biological tissue,exhibits excellent prospects in biological applications.This study aims to enhance the red upconversion emission intensity of Ho3+ions in NaLuF4∶20％Yb3+/2％Ho3+/12％Ce3+nanoparticles through building different core-shell structures with different excitation wavelengths.A significantly enhanced red upconversion emission with a higher red-to-green ratio was successfully obtained in NaLuF4∶20％Yb3+/2％Ho3+/12％Ce3+@NaLuF4 core-shell nanoparticles by introducing the Yb3+and Yb3+/Nd3+ions into the NaLuF4 shell,with enhancement of the red emission occurring when Yb3+and Nd3+ions in the shell transfer more exci-tation energy to the Ho3+ions.Investigation of the red emission enhancement mechanism is based on spectral characteristics and lifetimes.We examined the synergistic effect of dual-wavelength co-exci-tation NaLuF4∶20％Yb3+/2％Ho3+/12％Ce3+@NaLuF4∶10％Yb3+/15％Nd3+core-shell nanoparticles to establish optimal excitation conditions.It is hoped that this method,using red upconversion emission core-shell nanoparticles with multi-mode excitation,can provide new ways to expand the applications of rare-earth luminescent materials in biomedicine and anti-counterfeiting.