Mn2+ ions-activated phosphors play a crucial role in modern lighting and display due to their typical tunable single-band visible (VIS) emission characteristics. Herein, besides the conventional VIS emission, a near-infrared (NIR) emission centered at ∼780 nm is presented in heavy Mn2+-doped fluoride RbZnF3:Yb3+,Mn2+ designed by the dopant-distribution prediction simulation. On varying the dopant (Mn2+) concentration, the single-band VIS emission to VIS/NIR dual emission and then to pure NIR photon upconversion (UC) emission was achieved in RbZnF3:Yb3+,Mn2+. The density functional theory (DFT) calculations, static and dynamic luminescence analysis, as well as the extended-X-ray absorption fine structure (EXAFS) characterization strongly confirmed that the NIR emission of the Mn2+ was from the Mn2+–Mn2+ dimer induced by Mn2+ ions aggregation in RbZnF3. Further, a ground-state absorption (GSA)/excited state absorption (ESA) NIR UC luminescence mechanism based on the Yb3+–Mn2+–Mn2+ trimer model is proposed. This work provides a new strategy for realizing single-band NIR photon UC emission, and also provides new insights into the rational design of the Mn2+ VIS/NIR emission via dopant-distribution prediction.
Yb 3+ -Mn 2+ dimer based upconversion nanocrystals (UCNCs) have great prospects in biological and photonic applications. In this work, the broadband upconversion luminescence (UCL) of Yb 3+ -Mn 2+ dimer in perovskite nanocrystals is systematically engineered under multi-wavelength excitations. Under the excitation of 980, 940 and 915 nm lasers, KCdF 3 :Yb 3+ /Mn 2+ UCNCs generate yellow broadband UCL from Yb 3+ -Mn 2+ dimer at room temperature and achieve maximum intensity as Mn 2+ concentration reaches 7.5 mol%. By introducing Er 3+ ions into the KCdF 3 host matrix, the UCL color can be further tuned to pure red with high spectral purity, and the red-to-green (R/G) UC intensity ratio is promoted dramatically. The bidirectional energy transfer (ET) processes between Yb 3+ -Mn 2+ dimer, Mn 2+ and Er 3+ ions facilitate color modulation, supported by power dependence and lifetime measurements. Especially, the ET efficiency is evaluated under the multi-wavelength excitations, confirming the high efficiency of ET processes from Yb 3+ -Mn 2+ dimer to Er 3+ ions. Moreover, the obtained KCdF 3 :Yb 3+ /Mn 2+ /Er 3+ UCNCs present a maximum magnetization intensity of 2.01 emu/g when Mn 2+ concentration reaches 98.5 mol%. Both the tunable UCL and excellent paramagnetism properties indicate that these KCdF 3 :Yb 3+ /Mn 2+ /Er 3+ UCNCs have the capability of bifunctional biomarkers of nanomaterials and can be a candidate for bio-related applications.
The development of a luminescent material with visualized afterglow plays a crucial role in information security. Herein, a long-lived phosphor, KCaF3:Yb3+,Mn2+, with a visualized photon upconversion (UC) afterglow is presented. The UC emission spectrum consists of a high color purity (∼99.33%) yellow emission band peaking at ∼570 nm, and the UC afterglow signal can be observed by the naked eye in both bright and dark fields even at a high temperature of 200 °C. Moreover, the demonstration background and pigments have little influence on the UC afterglow identification. The density functional theory (DFT) calculations and the up-/down-conversion luminescence characteristics suggest that the UC afterglow originates from the long-lived exchange coupled Yb3+–Mn2+ dimers formed in KCaF3:Yb3+,Mn2+, which is independent of the conventional “afterglow trap”. The random distribution characteristics of Mn2+, and the oxygen ion (O2−) introduced by Yb3+ non-equivalent doping are the key factors for forming the efficient UC emission center in this system. Using the photon UC afterglow phosphor in screen printing ink, a visualized information encoding/decoding prototype suitable for both human and machine fast identification is demonstrated.
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