Two series of trivalent lanthanide and group 3 metal coordination polymers with 4′‐phenyl‐2,2′:6′,2′′‐terpyridine (ptpy) of the composition ¹_∞[MCl₃(ptpy)] (1, M = La, Ce, Pr, Nd) and the complexes [MCl₃(ptpy)(py)] (2, M = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) have been synthesized and characterized. For europium, the complex [Eu₂Cl₆(ptpy)₂] (3) was obtained as single crystals, its dimeric structure providing potential insight into the coordination polymer formation from monomeric entities. Product series 1 and 2 were photophysically investigated in the solid state at room temperature and 77 K. Alongside with standard ion‐specific 4f–4f trivalent lanthanide luminescence in the visible and NIR (of emitters such as europium, terbium, dysprosium, neodymium, etc.), visible range emission of praseodymium, holmium, erbium, and thulium was observed, which is rarely reported for coordination compounds. It occurs in addition to their characteristic NIR emission. For complexes of series 1, an exciplex based luminescence was observed originating from ligand π‐stacking in the crystal packing.

Praseodymium sulfate was obtained by the precipitation method and the crystal structure was determined by Rietveld analysis. Pr₂(SO₄)₃ is crystallized in the monoclinic structure, space group C2/c, with cell parameters a = 21.6052 (4), b = 6.7237 (1) and c = 6.9777 (1) Å, β = 107.9148 (7)°, Z = 4, V = 964.48 (3) ų (T = 150 °C). The thermal expansion of Pr₂(SO₄)₃ is strongly anisotropic. As was obtained by XRD measurements, all cell parameters are increased on heating. However, due to a strong increase of the monoclinic angle β, there is a direction of negative thermal expansion. In the argon atmosphere, Pr₂(SO₄)₃ is stable in the temperature range of T = 30–870 °C. The kinetics of the thermal decomposition process of praseodymium sulfate octahydrate Pr₂(SO₄)₃·8H₂O was studied as well. The vibrational properties of Pr₂(SO₄)₃ were examined by Raman and Fourier-transform infrared absorption spectroscopy methods. The band gap structure of Pr₂(SO₄)₃ was evaluated by ab initio calculations, and it was found that the valence band top is dominated by the p electrons of oxygen ions, while the conduction band bottom is formed by the d electrons of Pr³⁺ ions. The exact position of ZPL is determined via PL and PLE spectra at 77 K to be at 481 nm, and that enabled a correct assignment of luminescent bands. The maximum luminescent band in Pr₂(SO₄)₃ belongs to the ³P₀ → ³F₂ transition at 640 nm.

Humidity sensing properties of luminescent metal–organic framework (MOF) polymer mixed-matrix membranes (MMMs) ³ _∞[Ba_0.98Eu_0.02(Im)₂]@PSF (Im = imidazolate, PSF = polysulfone Ultrason® S), ³ _∞[Sr_0.90Eu_0.10(Im)₂]@PSF, and ³ _∞[Ce(Im)₃ImH]·ImH@PSF were investigated. MMMs show superior properties compared to bulk MOFs especially in stability, handling and long-term monitoring. In order to evaluate these films for such real status analyses, both their sensitivity and stability were determined and compared to bulk MOFs. Therefore, the progress of the humidity induced luminescence intensity quenching of the MMMs and the corresponding bulk substances was investigated for several pre-set relative humidities at room temperature. The MMMs show distinct and diverse luminescence loss and sensitivity rendering the monitoring of a very low relative humidity of only 2% accessible.