Selectively Manipulating Interactions between Lanthanide Sublattices in Nanostructure toward Orthogonal Upconversion

Smart control of ionic interactions is a key factor to manipulate the luminescence dynamics of lanthanides and tune their emission colors. However, it remains challenging to gain a deep insight into the physics involving the interactions between heavily doped lanthanide ions and in particular between the lanthanide sublattices for luminescent materials. Here we report a conceptual model to selectively manipulate the spatial interactions between erbium and ytterbium sublattices by designing a multilayer core-shell nanostructure. The interfacial cross-relaxation is found to be a leading process to quench the green emission of Er³⁺, and red-to-green color-switchable upconversion is realized by fine manipulation of the interfacial energy transfer on the nanoscale. Moreover, the temporal control of up-transition dynamics can also lead to an observation of green emission due to its fast rise time. Our results demonstrate a new strategy to achieve orthogonal upconversion, showing great promise in frontier photonic applications.

Upconversion Luminescence through Cooperative and Energy-Transfer Mechanisms in Yb3+ -Metal-Organic Frameworks

Lanthanide-doped metal-organic frameworks (Ln-MOFs) have versatile luminescence properties, however it is challenging to achieve lanthanide-based upconversion luminescence in these materials. Here, 1,3,5-benzenetricarboxylic acid (BTC) and trivalent Yb³⁺ ions were used to generate crystalline Yb-BTC MOF 1D-microrods with upconversion luminescence under near infrared excitation via cooperative luminescence. Subsequently, the Yb-BTC MOFs were doped with a variety of different lanthanides to evaluate the potential for Yb³⁺ -based upconversion and energy transfer. Yb-BTC MOFs doped with Er³⁺ , Ho³⁺ , Tb³⁺ , and Eu³⁺ ions exhibit both the cooperative luminescence from Yb³⁺ and the characteristic emission bands of these ions under 980 nm irradiation. In contrast, only the 497 nm upconversion emission band from Yb³⁺ is observed in the MOFs doped with Tm³⁺ , Pr³⁺ , Sm³⁺ , and Dy³⁺ . The effects of different dopants on the efficiency of cooperative luminescence were established and will provide guidance for the exploitation of Ln-MOFs exhibiting upconversion.

RGB Tricolor and Multimodal Dynamic Optical Information Encryption and Decoding for Anti-Counterfeiting Applications

Conventional optical anti-counterfeiting strategies are based on the single-color emission, which are easily deciphered and thus greatly limited in the application of information security. Herein, a multimodal dynamic optical information coding with red, green, and blue (RGB) tricolors has been developed by photoluminescence (PL), persistent luminescence (PersL), thermally stimulated luminescence (TSL), and thermally stimulated persistent luminescence (TSPL). The BaSi₂O₂N₂:Eu²⁺ phosphors with a blue emission peak at 494 nm were used as the crucial blue optical information coding material and exhibited the distinctive response properties to light, heat, and force stimuli with intrinsic trap depths of 0.674 and 0.82 eV. More importantly, by combining the red Sr₂Si₅N₈:Eu²⁺,Dy³⁺ and green SrSi₂O₂N₂:Eu²⁺,Dy³⁺ nitride phosphors, a RGB tricolor and multimodal strategy has been successfully developed for anti-counterfeiting applications. The "RGB tricolor flower" with RGB emissions is given as a typical example to achieve the dynamic display of optical information encryption and decoding through the various PL, PersL, TSL, and TSPL modes. Finally, the traditional quick response (QR) code mechanism has been integrated into the design of multi-information encrypted RGB tricolor anti-counterfeiting devices with different identifiabilities of the encrypted information in natural light, PL, PersL, TSL, and TSPL modes. The laminated layers of RGB QR code patterns containing different specific information, such as "DLPU" and "116034", can be effectively recognized in the corresponding modes. The design strategy of RGB tricolor and multimodal optical information encryption and decoding devices in this work greatly improves the security level of advanced optical information technologies and extends the potential applications in dynamic anti-counterfeiting fields.