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We have synthesized luminescent YVO 4 : Yb, Er nanoparticles (NPs) in the size range of 10-700 nm. A bright green luminescence of the dry NPs powder due to Er 3+ ions emission centered at 526 and 550 nm was compared for upconverting and downconverting laser excitations at 980 nm and 257 nm, respectively. Moreover, the NPs exhibited bright luminescence in colloidal water solution upon 980 nm laser irradiation. All experiments showed very weak radiative 4 F 9/2 → 4 I 15/2 emission from Er 3+ ions at 660 nm that indirectly indicates low efficiency of multiphonon intraionic transitions and insensitivity of the NPs to the luminescence quenchers in the water solution. A broad red band in the luminescence spectrum appearing under intense 257 nm laser excitation can be attributed to emission from crystal lattice defects in the NPs. Based on these facts we propose that YVO 4 : Yb, Er NPs are promising as efficient upconversion fluorescent nanoprobes for certain biological applications, like optogenetics.

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A synthetic method for a primary 2-(thiophen-2′-yl)ethylphosphine was developed. The reaction of thiophenylethylphosphine with paraformaldehyde and primary arylamines leads to the formation of cyclic bisphosphines, namely, 1,5-di(aryl)-3,7-bis(thiophenylethyl)-1,5-diaza-3,7-diphosphacyclooctane (aryl = phenyl, p-tolyl). The obtained bisphosphines form cationic bis-P,P-chelate complexes with copper(I) tetrafluoroborate, which were structurally characterized by NMR spectroscopy, mass spectrometry, and elemental and XRD analyses. Surprisingly, the copper(I) complexes display a multiband emission in the solid state with maxima at 355–360, 425–430, and 480–490 nm and nanosecond lifetimes (1.2–1.4 ns) upon a 335 nm excitation. The excitation of the complexes at 360 nm at room temperature results in a deep-blue emission at 425–430 nm and a tail at 460–490 nm. A temperature decrease leads to an increased intensity of the emission band at 480 nm, while the luminescence lifetimes insignificantly increased up to 14 ns. Quantum chemical calculations explain the observed unusual luminescent behavior by the existence of “undistorted” and “flattened” singlet excited states of copper(I) complexes at room temperature and at 77 K, respectively.