Investigation of upconversion and downconversion fluorescence emissions from β-NaLn1F4:Yb3+, Ln23+ (Ln1=Y, Lu; Ln2=Er, Ho, Tm, Eu) hexagonal disk system

Abstract Uniform hexagonal β-NaLn1F 4 :Yb 3+ , Ln2 3+ (Ln1 = Y, Lu; Ln2 = Er, Ho, Tm, Eu) disks were synthesized with hydrothermal method in which the sodium citrate was used as a shape modifier. The experimental observation indicated that both upconversion and downconversion fluorescence emissions were significantly stronger in β-NaLuF 4 than that for β-NaYF 4 . It was found that the stronger hypersensitive transitions were mainly due to the increase of J–O parameter ( Ω 2 ) in β-NaLuF 4 host, while the stronger insensitive transitions were mainly caused by the stronger overlap of electron cloud that was induced by the decrease of Ln F bond lengths. Additionally, the larger absorption strength in the near-infrared region is another important factor for the stronger fluorescence emissions. The current research has a great potential in improving near-infrared conversion efficiency of silicon solar cells.