Tailored Near‐Infrared Photoemission in Fluoride Perovskites through Activator Aggregation and Super‐Exchange between Divalent Manganese Ions

Abstract

Biomedical imaging and labeling through luminescence microscopy requires materials that are active in the near‐infrared spectral range, i.e., within the transparency window of biological tissue. For this purpose, tailoring of Mn2+–Mn2+ activator aggregation is demonstrated within the ABF3 fluoride perovskites. Such tailoring promotes distinct near‐infrared photoluminescence through antiferromagnetic super‐exchange across effective dimers. The crossover dopant concentrations for the occurrence of Mn2+ interaction within the first and second coordination shells comply well with experimental observations of concentration quenching of photoluminescence from isolated Mn2+ and from Mn2+–Mn2+ effective dimers, respectively. Tailoring of this procedure is achieved via adjusting the Mn–F–Mn angle and the Mn–F distance through substitution of the A+ and/or the B2+ species in the ABF3 compound. Computational simulation and X‐ray absorption spectroscopy are employed to confirm this. The principle is applied to produce pure anti‐Stokes near‐infrared emission within the spectral range of ≈760–830 nm from codoped ABF3:Yb3+,Mn2+ upon excitation with a 976 nm laser diode, challenging the classical viewpoint where Mn2+ is used only for visible photoluminescence: in the present case, intense and tunable near‐infrared emission is generated. This approach is highly promising for future applications in biomedical imaging and labeling.

Tuning Long‐Lived Mn(II) Upconversion Luminescence through Alkaline‐Earth Metal Doping and Energy‐Level Tailoring

“…The lifetimes for the yellow and green emissions were estimated to be 65 and 20 ms, respectively. The yellow emission displayed a record lifetime for Mn 2+ as compared with previous reports . Interestingly, the emergence of the new emitting center has a marginal effect on the green emitting sites because it essentially showed unchanged decay kinetics (20 ms) at different doping levels of Ca 2+ (Figure S8, Supporting Information).…”

Interaction between the exchanged Mn2+ and Yb3+ ions confined in zeolite-Y and their luminescence behaviours

“…6a, while those samples ( x  = 0, 0.2, 0.4, 0.6) exhibit no apparent UC emissions. Since there is a large gap between the first excited state of 4 T 1 and ground state of 6 A 1 for Mn 2+ (normally > 17,000 cm −1 ) and there is no metastable excited state above 10,000 cm −1 for Yb 3+ ion2627282930, it normally requires the vicinity of Mn 2+ -Yb 3+ ions in the lattice for super exchange-interaction or cooperative sensitization based UC process. Therefore, when Mn 2+ content is high enough ( x  ≥ 0.8), the Mn 2+ ions tend to show up at the neighbor of Yb 3+ ions.…”

“…Meanwhile, upconversion (UC) emission of Mn 2+ could be realized by codoping Yb 3+ in the Mn 2+ doped materials27. It generally requires the vicinity of Mn 2+ -Yb 3+ ions in the lattice for superexchange-interaction or cooperative sensitization based UC process, because there is a large gap between the first excited (emissive) state 4 T 1 and the ground state 6 A 1 for Mn 2+ (normally >17,000 cm −1 ) while there is no metastable excited state above 10,000 cm −1 for Yb 3+ ion2627282930. Therefore, Mn 2+ -Yb 3+ codopants may be an option in the zeolite-Y host to check their interaction and energy transfer involved.…”

Tuning Mn4+ Red Photoluminescence in (K,Rb)2Ge4O9:Mn4+ Solid Solutions by Partial Alkali Substitution

“…Currently, research interest has concentrated on the development of cost‐effective and eco‐friendly red phosphors beyond the use of rare earth ingredients. For example, transition metal ions such as Bi 2+ , Cr 3+ , Mn 2+ , and Mn 4+ have been investigated as activator species in deep‐red‐emitting phosphors . Peng et al reported new candidates of red phosphors activated by Bi 2+ , which absorb both near‐UV and blue light and emit intense red light .…”

“…Research on Cr 3+ ion therefore mainly focuses on persistent luminescence and potential application in near‐infrared bio‐imaging or photodynamic tumor therapy . Mn 2+ single doped phosphors cannot be used for pc‐WLEDs due to their low absorption in the near‐UV or blue spectral region . In contrast with the isoelectronic Cr 3+ ion, Mn 4+ doped materials have now been widely reported for lighting, holography, laser technology, dosimetry, and optical data storage .…”