We report the synthesis, crystal structures, and optical properties of two new compounds, KBiI(I)·14HO (1) and (NH)BiI(I)·4.5HO (2), as well as the electronic structure of the latter. They crystallize in tetragonal space group P4/ mmm with the unit cell parameters a = 12.974(1) and c = 20.821(3) Å for 1 and a = 13.061(3) and c = 15.162(7) Å for 2. Though 1 and 2 are not isomorphous, their crystal structures display the same structural organization; namely, the BiI octahedra are linked by I units to form disordered layers in 1 and perfectly ordered chains in 2. The I-I bond distances in the thus formed I-I-I-I linear links are not uniform; the central bond is only slightly longer than in a standalone I molecule, whereas the peripheral bonds are significantly shorter than longer bonds typical for various polyiodides, which is confirmed by Raman spectroscopy. The analysis of the electronic structure shows that the atoms forming the I-I-I-I subunits transfer electron density from their occupied 5p orbitals onto their vacant states as well as onto 6s orbitals of bismuth atoms that center the BiI octahedra. This leads to low direct band gaps that were found to be 1.57 and 1.27 eV for 1 and 2, respectively, by optical absorption spectroscopy. Luminescent radiative relaxation was observed in the near-IR region with emission maxima of 1.39 and 1.24 eV for 1 and 2, respectively, in good agreement with the band structure, despite the strong quenching propensity of I moieties.

Searching for new NIR emitting materials, lanthanide 9-anthracenates Ln(ant)3 were synthesized and thoroughly characterized. Ytterbium 9-anthracenate Yb(ant)3, that demonstrated the highest NIR luminescence efficiency, was successfully used as an emission layer of a host-free OLED and its electroluminescence quantum efficiency, corresponding to the sole band at 1000 nm, reached 0.21%. This performance could be achieved due to the high quantum yield of Yb(ant)3, which reached 1.5% and was increased up to 2.5% by partial Yb3+ substitution with Lu3+, as well as its high electron mobility due to the extended stacking in its crystal structure. The first gadolinium-based PHOLED was prepared based on Gd(ant)3

Highly luminescent, photostable, and soluble lanthanide pentafluorobenzoates have been synthesized and thoroughly characterized, with a focus on Eu(III) and Tb(III) complexes as visible emitters and Nd(III) , Er(III) , and Yb(III) complexes as infrared emitters. Investigation of the crystal structures of the complexes in powder form and as single crystals by using X-ray diffraction revealed five different structural types, including monomeric, dimeric, and polymeric. The local structure in different solutions was studied by using X-ray absorption spectroscopy. The photoluminescence quantum yields (PLQYs) of terbium and europium complexes were 39 and 15 %, respectively; the latter value was increased almost twice by using the heterometallic complex [Tb0.5 Eu0.5 (pfb)3 (H2 O)] (Hpfb=pentafluorobenzoic acid). Due to the effectively utilized sensitization strategy (pfb)(-) →Tb→Eu, a pure europium luminescence with a PLQY of 29 % was achieved.

Depending on the local excess of lanthanide ions (Ln = Lu, Yb, Er, Dy, Tb, Gd, Eu, Nd) or 2-(tosylamino)-benzylidene-N-benzoylhydrazone (H2L), lanthanide complexes, containing either a mono-deprotonated ligand (Ln(HL)2X, X = Cl, NO3) or both mono- and dideprotonated ligands (Ln(L)(HL)), were preparatively obtained. The crystal structures of Lu(HL)2Cl, Yb(L)(HL)(H2O)2, Yb(L)(HL)(EtOH)2(H2O) and Er(L)(HL), determined by single crystal diffraction data or from powder diffraction data using Rietveld refinement, have shown the surprising resemblance. The study of luminescence temperature dependence of Eu(HL)2Cl and Eu(L)(HL) showed that europium luminescence is quenched by thermally-activated 5D0 → T1 energy transfer. Luminescent thermometers based on these complexes demonstrated the sensitivity of up to 7.7% at 85 K which is the highest value above liquid-nitrogen temperatures obtained to date.

Lanthanide complexes Ln(L 1 )(HL 1 ) (Ln = Lu, Yb, Er, Gd, Eu, Sm) and Ln(L 2 )(HL 2 ) (Ln = Lu, Yb, Gd, Eu) with 2-(tosylamino)-benzylidene-N-(aryloyl)hydrazones (H 2 L 1 , aryloyl = 2-hydroxybenzoyl; H 2 L 2 , aryloyl = isonicotinoyl) were obtained with the aim to explore them as new luminescent materials. They were found to form monomeric species independently on the aryloyl group, and their crystal structures were determined from single-crystal Xray data (Yb(L 2 )(HL 2 )•0.5(C 2 H 5 OH)), as well as from powder X-ray data by Rietveld refinement (Eu(L 1 )(HL 1 )). Ytterbium complexes exhibited intense luminescence, which allowed using them in host-free organic light-emitting diodes, which demonstrated remarkable efficiency of near infrared electroluminescence (50 μW/W) at low voltage (5 V). The special mechanism of europium luminescence quenching allowed using europium complexes as luminescent thermometers, which demonstrated very high sensitivity up to 12%/K. The theory of luminescence thermometry based on a three-level system was proposed, which allowed predicting sensitivity with high accuracy (error within 20%).

Lanthanide complexes LnL3 (Ln = Sm, Eu, Tb, Dy, Tm, Yb, Lu) with aromatic o-phosphorylated ligands (HL(1) and HL(2)) have been synthesized and identified. Their molecular structure was proposed on the basis of a new complex approach, including DFT calculations, Sparkle/PM3 modelling, EXAFS spectroscopy and luminescent probing. The photophysical properties of all of the complexes were investigated in detail to obtain a deeper insight into the energy transfer processes.

The search for precursors of luminescent biomarkers is carried out among highly luminescent, stable, and soluble lanthanide p‐substituted fluorobenzoates, which were synthesized and thoroughly characterized. Examination of their crystal structure revealed the dependence of the structure on the lanthanide ion and on the separation method, because of the high acidity of the selected compounds. The brightness of the luminescence of the terbium and europium complexes varies significantly with both absorption and photoluminescence quantum yields (PLQYs), and the latter reaches 62 %.

We have synthesized Eu(iii) ternary complexes possessing record photoluminescence yields up to 90%. This high luminescence performance resulted from the absence of quenching moieties in the Eu coordination environment and an efficient energy transfer between ligands, combined with a particular symmetry of the coordination environment.