An efficient pink luminescent Eu(iii) coordination polymer excited on a blue LED chip

Two new sets of lanthanide-based coordination polymers (CPs), [Ln(DHTP)(NO₃)(H₂O)₄]_n [Ln1 = Gd1, Eu1] and [Eu₂(DHTP)(TTA)₄(DMF)₂(MeOH)₂]_n (Eu2) using 2,5-dihydroxyterephthalic acid (DHTP) and incorporating thenoyltrifluoroacetone (TTA) units, have been synthesized via condensation reactions and characterized. The single-crystal X-ray diffraction studies revealed that the Eu1 CP has a 2D zig-zag chain while the Eu2 CP exhibits a 2D polymeric structure derived from dinuclear Eu(iii) building blocks. A detailed photoluminescence study proved that the band structure of the DHTP ligand is suitable for the luminescence sensitization of Eu(iii). Efficient red emission is observed for the Eu(iii) polymers in the solid state with a fairly large luminescence intrinsic quantum yield (Q_Eu) of 52% from the Eu2 CP. Finally, a light emitting diode (LED) was fabricated by using a resin of 10% Eu2 CP-silicon oil as the emitting layer over an InGaN blue LED chip. Interestingly, the Eu2/InGaN LED displays pink light with CIE 1931 chromaticity coordinates of (0.437, 0.185).