An further enhancement in red upconversion emission in single LiYbF₄: Ho³⁺ microparticle through codoping Ce³⁺ ions

In this work, tetragonal-phase LiYF₄:Yb³⁺/Ho³⁺ and LiYbF₄:Ho³⁺ microparticles were successfully synthesized and excited by near-infrared laser at 980 nm through a confocal microscopy system. Upconversion (UC) emission tuning from green to red in single LiYF₄:Yb³⁺/Ho³⁺ and LiYbF₄:Ho³⁺ microparticles was achieved by increasing the Yb³⁺ and Ce³⁺ ion concentrations, respectively. A high intensity ratio of red to green emission was obtained in single LiYbF₄:Ho³⁺ microparticle codoped with 12% Ce³⁺, which was boosted by approximately 19-fold in single LiYF₄:Yb³⁺/Ho³⁺ microparticle. The cross-relaxation processes between adjacent Ho³⁺ ions, Yb³⁺ and Ho³⁺ ions, and Ho³⁺ and Ce³⁺ ions have been employed to enhance red UC emission and suppress green UC emission. The regulation mechanisms of UC emission of Ho³⁺ ions are discussed based on the emission spectra. The marked pure single-band red UC emission of single LiYbF₄: Ho³⁺ microparticle can be applied in multicolor display technology and micro-optoelectronic devices.