Colloidal nanoparticles of a europium complex with enhanced luminescent properties

We report an alternative approach, that is, forming Eu(tta)(3)dpbt (dpbt = 2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine, tta = thenoyltrifluoroacetonato) nanoparticles in water/methanol mixtures, to satisfy the combined requirements of good dispersibility in water solutions and efficient long-wavelength sensitization for Eu-III complexes to be used in biological applications. The size of Eu(tta)(3)dpbt colloidal particles with very high luminescent capabilities can be modulated to some extent by changing the preparation conditions. The optical excitation window for the Eu-III luminescence of Eu(tta)(3)dpbt nanoparticles, extending up to 475 nm, is wider than that of Eu(tta)(3)dpbt molecules dissolved in toluene. This is the first example for obviously extending the sensitization window of luminescent lanthanide materials to the long-wavelength region by forming nanoparticles of a lanthanide complex. Quantum yields of Eu-III luminescence of the prepared Eu(tta)(3)dpbt colloidal particles, with an average diameter of 33.1 nm, are 0.27, 0.27, 0.24, 0.19, 0.14, and 0.01 upon excitation at 402, 420, 430, 440,450, and 475 nm, respectively. The Eu(tta)(3)dpbt nanoparticles exhibited excellent two-photon sensitization performance with a highest 6(D value of 3.2 x 10(5) GM (1 GM = 10(-50) cm(4) s photo(-1) particle(-1)) at the excitation wavelength of 832 nm, which is about 7 times higher than the highest value reported for the CdSe/ZnS core-shell quantum dots. The favorable luminescent properties and the good dispersibility in water solutions of the Eu(tta)(3)dpbt nanoparticles are very promising for the development of new luminescent nanoprobes for bioanalysis.