Near-IR to Near-IR Upconversion Luminescence in Molecular Chromium Ytterbium Salts.

Jens Kalmbach,Katja Heinze,Hartmut Schubert,Michael Seitz,Cui Wang,Ute Resch‐Genger,Christoph Förster,Yi You

doi:10.1002/anie.202007200

Abstract

Upconversion photoluminescence in hetero‐oligonuclear metal complex architectures featuring organic ligands is an interesting but still rarely observed phenomenon, despite its great potential from a basic research and application perspective. In this context, a new photonic material consisting of molecular chromium(III) and ytterbium(III) complex ions was developed that exhibits excitation‐power density‐dependent cooperative sensitization of the chromium‐centered 2E/2T1 phosphorescence at approximately 775 nm after excitation of the ytterbium band 2F7/2→2F5/2 at approximately 980 nm in the solid state at ambient temperature. The upconversion process is insensitive to atmospheric oxygen and can be observed in the presence of water molecules in the crystal lattice.

Highlights

Metal-based upconversion (UC) transforming low-energy photons into an anti-Stokes-shifted luminescence is a very attractive non-linear process for fundamental studies as well as for future applications
This includes metal chelate-organic chromophore combinations,[6] mononuclear metal complexes,[7] and hetero-oligometallic sensitizer–activator architectures.[8,9]. The latter have shown to hold the greatest potential for efficient UC, especially for energy transfer upconversion (ETU) and for cooperatively sensitized upconversion (CSU)
By carefully revisiting earlier downshifting Cr3+/Yb3+ systems, we realized a novel near-IR to near-IR upconversion (UC) material by combining Cr3+ and Yb3+ complexes in an ionic solid

Summary

Introduction

Metal-based upconversion (UC) transforming low-energy photons into an anti-Stokes-shifted luminescence is a very attractive non-linear process for fundamental studies as well as for future applications. Plexes[3] due to the pronounced non-radiative deactivation of the excited metal states by high-frequency oscillators present in organic ligands like -OH, -NH or -CH groups.[4] In the past few years, many advances have been achieved in implementing metal-based UC in molecular complex species, some even at ambient temperature and in solution.[5] This includes metal chelate-organic chromophore combinations,[6] mononuclear metal complexes,[7] and hetero-oligometallic sensitizer–activator architectures.[8,9] The latter have shown to hold the greatest potential for efficient UC, especially for energy transfer upconversion (ETU) and for cooperatively sensitized upconversion (CSU) For both UC schemes, sensitizer metal centers (S) with appropriate energy levels and sufficiently long luminescence lifetime are necessary to successfully populate an activator (A) excited state with approximately twice the energy of the excited sensitizer state at relatively low excitation power densities. This led to a new photonic material composed of accessible Cr3+ and Yb3+ complex ions which shows 2E/2T1 UC at room temperature already at relatively low excitation power densities

Results and Discussion

Conclusion

Conflict of interest