Circularly Polarized Luminescence from Pure and Eu-Doped Trigonal TbPO·HO Nanocrystals.

In this contribution, we describe the preparation, by means of a precipitation reaction from aqueous solution at 40 °C, and the structural characterization of nanocrystalline powders of trigonal TbEuPO·HO (with = 0, 0.005, 0.01, 0.05, and 0.1; tentatively assigned as 0.67) which crystallize in the two possible 321 or 321 enantiomorphic space groups. While the volume of the crystal lattice is not significantly affected by the Tb/Eu substitution, the average crystallite size seems to depend on the Eu dopant concentration and ranges from 13 to 30 nm. The desired handedness of the crystals has been induced by using, during the synthesis, one of the two possible enantiomers of tartaric acid (l or d). The analysis of the luminescence excitation and emission spectra, together with the decay kinetics of the D Tb excited state, suggests the presence of a very efficient Tb → Eu energy transfer process in the Eu-doped orthophosphates. Upon excitation of Tb ions at 368 nm, the enantiomorphic powders grown with l- or d-tartaric acid (i.e., l-TbPO·0.67HO/d-TbPO·0.67HO, l-TbEuPO·0.67HO/d-TbEuPO·0.67HO, and l-TbEuPO·0.67HO/d-TbEuPO·0.67HO) exhibited mirror circularly polarized luminescence signals in the visible spectral region (in the green and/or in the red).