Ana Kuzmanoski

1,3-Thiazole as Suitable Antenna Ligand for Lanthanide Photoluminescence in [LnCl3(thz)4]·0.5thz, Ln = Sm, Eu, Gd, Tb, Dy

The series of luminescent monomeric lanthanide thiazole complexes [LnCl3(thz)4]⋅0.5thz (Ln = Sm, Eu, Gd, Tb, Dy; thz=1,3-thiazole) has been synthesised and characterised by powder and singlecrystal X-ray diffraction, IR and photoluminescence spectroscopy, DTA/TG as well as elemental analysis. The colourless compounds exhibit photoluminescence in the visible region with varying quantum efficiencies up to QY = 48% for [TbCl3(thz)4]⋅0.5thz. Both, the lanthanide ions as well as the thiazole ligand contribute to the luminescence. Excitation can be achieved via intra-4 f transitions and by exciting the ligand, emission is observed mainly from the lanthanide ions again by 4 f transitions. Thiazole can transfer energy to the lanthanide ions, which further feeds the lanthanide emission by an efficient antenna effect even at room temperature. The lanthanide ions show pentagonalbipyramidal coordination by three chloride anions and four N atoms of 1,3-thiazole, which leads to a strong 5D0 →7F4 transition for europium. Significant differences arise as compared to thiophene complexes because no sulphur atom is involved in the metal coordination, as the thiazole ligand is solely coordinated via its nitrogen function. Graphical Abstract 1,3-Thiazole as Suitable Antenna Ligand for Lanthanide Photoluminescence in [LnCl3(thz)4]·0.5thz, Ln = Sm, Eu, Gd, Tb, Dy

Microwave-Assisted Polyol Synthesis of Water Dispersible Red-Emitting Eu3+-Modified Carbon Dots

Eu3+-modified carbon dots (C-dots), 3–5 nm in diameter, were prepared, functionalized, and stabilized via a one-pot polyol synthesis. The role of Eu2+/Eu3+, the influence of O2 (oxidation) and H2O (hydrolysis), as well as the impact of the heating procedure (conventional resistance heating and microwave (MW) heating) were explored. With the reducing conditions of the polyol at the elevated temperature of synthesis (200–230 °C), first of all, Eu2+ was obtained resulting in the blue emission of the C-dots. Subsequent to O2-driven oxidation, Eu3+-modified, red-emitting C-dots were realized. However, the Eu3+ emission is rapidly quenched by water for C-dots prepared via conventional resistance heating. In contrast to the hydroxyl functionalization of conventionally-heated C-dots, MW-heating results in a carboxylate functionalization of the C-dots. Carboxylate-coordinated Eu3+, however, turned out as highly stable even in water. Based on this fundamental understanding of synthesis and material, in sum, a one-pot polyol approach is established that results in H2O-dispersable C-dots with intense red Eu3+-line-type emission.

Tb2(bpdc)3 and Eu2(bpdc)3 Nanoparticles (bpdc: 2,2ʹ-Bipyridine-4,4ʹ- dicarboxylate) and Their Luminescence

Tb2(bpdc)3 and Eu2(bpdc)3 nanoparticles (bpdc: 2,2ʹ-bipyridine-4,4ʹ-dicarboxylate) have been prepared via straightforward precipitation from aqueous solution. The nanoparticles exhibit mean diameters of 41(5) nm (Tb2(bpdc)3) and 56(4) nm (Eu2(bpdc)3) and show a very good colloidal stability in aqueous suspension. Particle size and chemical composition have been characterized based on electron microscopy, X-ray diffraction, infrared spectroscopy and thermogravimetry. Photoluminescence validates an efficient excitation of Tb3+/Eu3+ via the bpdc ligand as an antenna that leads to intense characteristic green and red emissions. The absolute quantum yields of Tb2(bpdc)3 and Eu2(bpdc)3 have been determined at 28 and 12%, respectively. Although rare-earth metal-based photoluminescence is typically quenched in water due to vibronic loss processes (v(O-H)), here, the antenna effect and the shielding of the metal centers via the bpdc ligand are very efficient, allowing for an intense green and red emission of the Tb2(bpdc)3 and Eu2(bpdc)3 nanoparticles even in aqueous suspension. Graphical Abstract Tb2(bpdc)3 and Eu2(bpdc)3 Nanoparticles (bpdc: 2,2ʹ-Bipyridine-4,4ʹ- dicarboxylate) and Their Luminescence