Large Upconversion Enhancement in the "Islands" Au-Ag Alloy/NaYF4: Yb3+, Tm3+/Er3+ Composite Films, and Fingerprint Identification

• Published in: Advanced functional materials Vol. 25; no. 34; pp. 5462 - 5471
• Main Authors: Chen, Xu, Xu, Wen, Zhang, Lihang, Bai, Xue, Cui, Shaobo, Zhou, Donglei, Yin, Ze, Song, Hongwei, Kim, Dong-Hwan
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 09.09.2015
• Subjects: Au-Ag alloy; fingerprint identification; surface plasmons; upconversion luminescence
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201502419

The surface plasmon (SP) modulation is a promised way to highly improve the strength of upconversion luminescence (UCL) and expand its applications. In this work, the “islands” Au–Ag alloy film is prepared by an organic removal template method and explored to improve the UCL of NaYF4: Yb3+, Tm3+/Er3+. After the optimization of Au–Ag molar ratio (Au1.25–Ag0.625) and the size of NaYF4 nanoparticles (NPs, ≈7 nm), an optimum enhancement as high as 180 folds is obtained (by reflection measurement) for the overall UCL intensity of Tm3+. Systematic studies indicate that the UCL enhancement factor (EF) increases with the increased size of metal NPs and the increase of diffuse reflection, with the decreased size of NaYF4 NPs, with the decreased power density of excitation light and with improving order of multiphoton populating. The total decay rate varies only ranging of about 20% while EF changes significantly. All the facts above indicate that the UCL enhancement mainly originates from coupling of SP with the excitation electromagnetic field. Furthermore, the fingerprint identification based on SP‐enhanced UCL is realized in the metal/UC system, which provides a novel insight for the application of the metal/UC device. An “islands” Au–Ag/NaYF4: Yb3+, Tm3+ composite film is prepared by an organic self‐assembly and removal template method. The Au–Ag alloy has the stable and repeatable properties and exhibits super‐broad surface plasmon resonance band extending to 1100. It obtained ≈180‐fold enhancement of upconversion luminescence for fingerprint identification.