Blue, Blue, Stable Optical Blue…

An international team suggest that coordination network materials, in particular MOFs, will be a useful platform for low-threshold lasers for diverse applications.

Metal-organic-framework (MOF)-based solid-state dielectrics, which can outperform nonlinear and optical gain materials based on dyes in solution/liquid/fluid systems known to have stability issues and therefore limited practical applicability, has been developed by an international team of authors.

Roland Fischer and colleagues from the Technical Universities of Munich and Dortmund and from Nanyang Technical University observed blue-color stimulated emission with low threshold power from In- and Zn-MOFs, which feature a highly fluorescent chromophore densely packed and rigidly linked to the metal-ion centers in the solid state. Rather than including dyes in the cavities within the MOFs the researchers used the emission dye as an organic linker making up the structure.

Anionic blue phosphor 3D interpenetrated MOFs without any dye loading or doping and in the absence of external cavity exhibited intrinsic STE properties depending on the packing density and on the arrangement of the linker molecules in the MOFs. Excited with a 400 nm laser the materials emit in the blue region, around 450-475 nm. Lower threshold powers were observed for the Zn-MOF attributed to the denser packing of linkers in the material and exceptionally high nonlinear absorption with 2-photon excited fluorescence (2PEF) action cross-section values up to 3072 GM were found for the In-MOF, the highest value for any hybrid solid state material so far.

The MOF-based materials not only exhibited unique optical properties but also high photo- and thermal-stability, properties assigned to the conformational rigidity and packing of the organic linkers that are pinned between the metal-ion nodes of the framework. The authors therefore suggest that coordination network materials, in particular MOFs, will be a useful platform for low-threshold lasers for diverse applications ranging from communication technology to medical sciences.

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