Near-infrared (NIR) luminescent Yb(III) complexes composed of low-vibrational frequency (LVF) fluorinated acetylacetonate and phosphine oxide ligands are reported. Their structures are determined using X-ray single-crystal analyses and categorized as eight-coordinated square antiprism. The radiative rate constants (kr), the nonradiative rate constants (knr), and the 4f–4f emission quantum efficiency (ΦEm) are estimated using their absorption spectra of magnetic dipole transition in Yb(III) complexes (2F5/2 → 2F7/2) and the observed emission lifetimes. Characteristic NIR luminescence properties of Yb(III) complexes with LVF phosphine oxide and fluorinated acetylacetonate ligands are elucidated in terms of the radiative and nonradiative rate constants.

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A 20-year-old man presented with pain and recurrent hemarthrosis in the right knee. Magnetic resonance imaging of the knee showed a lesion with homogeneous low signal intensity on T1-weighted images and a heterogeneous, low to high signal intensity on T2-weighted images. At arthroscopy, the mass was located between the posterior cruciate ligament and the posterior knee joint capsule. The tumor was excised through a posterior approach and histologically diagnosed as a nodular fasciitis. Intra-articular nodular fasciitis is a very rare clinicopathologic entity. The current case showed the unique clinical feature of recurrent hemarthrosis at initial presentation, which has not been previously reported.

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