Effective Green Upconversion Luminescence of Tb3+Ion by Indirect Sensitization

摘要

This paper reports the strong indirect up-conversion sensitizationluminescent phenomenon of Tb3+ ion’s 5D4 level in organic complexes. Itwas found that the green up-conversion photoluminescence (PL) wascoming out at 494nm, 545nm and 584nm pumped by 650nm line of OPO.These emission lines correspond to the 4f-4f transitions of Tb3+ ion,5D4→7F6, 5D4→7F5 and 5D4→7F4 respectively. The phenomenon from thosecomplexes was observed in both solution and solid form. Moreover, the upconversionluminescent efficiency was enhanced by optimizing theconcentration of solution. The reason of the strong indirect up-conversionluminescence was probably explained in a two-step process. The first step isthe two-photon absorption of organic ligand due to phonon-assistedexcitation. The second step is the energy transfer from the lowest tripletstate of ligand to the 5D4 state of Tb3+ ion. The PL intensity changed againsttemperature, pumping energy, concentration of solution was measured anddiscussed. It reflects the mechanism of this up-conversion luminescentprocess. Their up-conversion spectra had a broad excitation band. Thelifetime both up-conversion and down-conversion was similar in the rangeof 0.3-1.5ms. The up-conversion luminescent efficiency was up to about 1%compared to normal luminescence. The significance of this result is that it ispossible to find some organic materials having high upconversion efficiencyto apply in biochemistry imaging and 3D display.