Abstract
The development of luminescent inorganic nanocrystals (NCs) doped withrare-earth (RE) ions has attracted increasing interest owing to their distinctoptical properties and versatile applications in time-resolved bioassays,multiplex biodetection, DNA hybridization and bioimaging. HexagonalTbPO4:Eu3 + NCs (10–30 nm) were synthesized via a facile hydrothermal method assisted with oleic acid (OA)surfactants, which exhibit tunable emissions from green to red by varying the concentration ofEu3 + . TheTb3 + -to-Eu3 + energy transfer efficiency observed reaches up to 94%. Different from theirbulk counterparts, a new interface-state band (316 nm) in addition to thecommonly observed spin-forbidden 4f–5d transition band (265 nm) ofTb3 + wasfound to be dominant in the excitation spectrum of NCs due presumably to the formation of surfaceTbPO4/OA complexes,which provides an additional excitation antenna in practical utilization. Two kinds of luminescence sitesof Eu3 + inTbPO4 NCs, with the sitesymmetry of C2 or C1, were identified based on the emission spectra at 10 K and roomtemperature. Furthermore, the photoluminescence (PL) dynamics ofTb3 + ions inpure TbPO4 NCs have been revealed. Compared to the exponential PL decay in bulk counterpartsinduced by very fast energy migration, the non-exponential decay from 5D4 ofTb3 + inTbPO4 NCsis mainly attributed to the diffusion-limited energy migration due to more rapid energy transfer fromTb3 + to defects than theenergy migration among Tb3 + .
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