Significantly Boosted Upconversion Emission in Cryogenic Er@Yb@Y Core–Shell–Shell Nanostructures

• Published in: Advanced optical materials 2024-02, Vol.12 (5), p.n/a
• Main Authors: Wang, Enhui, Wang, Wei, Niu, Lujun, Feng, Yansong, Zhao, Haifeng, Luo, Yongshi, Zhang, Ligong, Li, Qiqing, Chen, Haoran, Chang, Yulei, Tu, Langping, Zhang, Hong, Zuo, Jing
• Format: Article
• Language: English
• Subjects: cross relaxation; Erbium; Fluorides; information encryption; Low temperature; low temperatures; Nanomaterials; Nanostructure; nanostructures; Shells (structural forms); Sodium compounds; Temperature; Temperature dependence; Upconversion; Ytterbium; Yttrium
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.202301827

Recent advances reveal that due to the cross‐relaxation restriction, impressive upconversion (UC) enhancement (≈100‐folds) can be achieved in cryogenic Er3+‐rich core‐inert shell nanostructures (e.g., NaErF4@NaYF4), which opens up exciting opportunities in diverse frontier applications. However, further promotion of UC intensity is still highly desired, in which the rational design of nanostructures can play a key role. Herein, it is demonstrated that adopting an active shell design will constantly benefit the UC within a wide temperature range (40–300 K). Specifically, through constructing the luminescent core@active shell@inert shell sandwich nanostructure (e.g., NaErF4@NaYbF4@NaYF4), 8.3–73‐folds UC enhancement will be achieved (taking the corresponding core@inert shell structures as competitors). Moreover, from spectral‐domain and time‐domain spectroscopic experiments, the relevant UC enhancement is convincingly attributed to a temperature‐dependent energy injection process (from the active shell to the luminescent core). More interestingly, the unique property of the material makes a temperature‐induced high‐level encryption application possible, which is obtained by employing the nanomaterials on a quick response (QR) code. These results not only deepen the UC mechanism in multi‐layer nanostructures, but also introduce an expanded dimension (via low temperatures) in information security. The advantages of active shell sensitization and the cryogenic field‐induced cross relaxation suppression are combined in this study, which significantly promotes the upconversion emission brightness of Er3+‐rich core–shell nanostructures 1–2 orders of magnitude. Based on the unique property of the material, a temperature‐induced high‐level information encryption application with QR code is successfully developed.