Luminescence properties of europium-doped Ca_10-xEu_x(PO₄)₆(OH)₂ (x_Eu = 0, 0.01, 0.02, 0.10 and 0.20) and gadolinium-doped hydroxyapatite Ca_9.80Gd_0.20(PO₄)₆(OH)₂ (HA), synthesized via solid-state reaction at T = 1300 °C, were investigated using scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR), and luminescence spectroscopy. Crystal structure characterization (from unit cell parameters determination to refined atomic positions) was achieved in the P6₃/m space group. FTIR analyses show only slight band shifts of (PO₄) modes as a function of the rare earth concentration. Structural refinement, achieved via the Rietveld method, and luminescence spectroscopy highlighted the presence of dopant at the Ca2 site. Strong luminescence was observed for all Eu- and Gd-doped samples. Our multi-methodological study confirms that rare-earth (RE)-doped synthetic hydroxyapatites are promising materials for bio-imaging applications.

$C{a}_{2.90}M{e}_{0.10}^{2+}{\left(P{O}_4\right)}_2$ (with Me = Mn, Ni, Cu) β-tricalcium phosphate (TCP) powders were synthesized by solid-state reaction at T = 1200 °C and investigated by means of a combination of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, and luminescence spectroscopy. SEM morphological analysis showed the run products to consist of sub spherical microcrystalline aggregates, while EDS semi-quantitative analysis confirmed the nominal Ca/Me composition. The unit cell and the space group were determined by X-ray powder diffraction data showing that all the compounds crystallize in the rhombohedral R3c whitlockite-type structure, with the following unit cell constants: a = b = 10.41014(19) Å, c = 37.2984(13) Å, and cell volume V = 3500.53(15) ų (Mn); a = b = 10.39447(10) Å, c = 37.2901(8) Å; V = 3489.22(9) ų (Ni); a = b = 10.40764(8) Å, c = 37.3158(6) Å, V = 3500.48(7) ų (Cu). The investigation was completed with the structural refinement by the Rietveld method. The FTIR spectra are similar to those of the end-member Ca β-tricalcium phosphate (TCP), in agreement with the structure determination, and show minor band shifts of the (PO₄) modes with the increasing size of the replacing Me²⁺ cation. Luminescence spectra and decay curves revealed significant luminescence properties for Mn and Cu phases.

In the search for new multifunctional materials, particularly for application in solid-state lighting, a set of terbium salicylato (Sal) complexes of general composition [Cat][Tb(Sal)₄] with the commonly ionic liquid-forming (IL) cations [Cat] = (2-hydroxyethyl)trimethylammonium (choline) (Chol⁺), diallyldimethylammonium (DADMA⁺), 1-ethyl-3-methylimidazolium (C₂C₁Im⁺), 1-butyl-3-methylimidazolium (C₄C₁Im⁺), 1-ethyl-3-vinylimidazolium (C₂Vim⁺), and tetrabutylphosphonium (P₄₄₄₄⁺) were synthesized. All Tb compounds exhibit strong green photoluminescence of high color purity by energy transfer from the ligand in comparison with what the analogous La compounds show, and quantum yields can reach up to 63% upon ligand excitation. When excited with an HF generator, the compounds show strong green electroluminescence with the same features of mission. The findings promise a high potential of application as emitter materials in solid-state lighting. As an additional feature, the Tb compounds show a strong response to applied external fields, rendering them multifunctional materials.

Many crystalline materials form polymorphs and undergo solid–solid transitions between different forms as a function of temperature or pressure. However, there is still a poor understanding of the mechanism of transformation. Conclusions about the transformation process are typically drawn by comparing the crystal structures before and after the conversion, but gaining detailed mechanistic knowledge is strongly impeded by the generally fast rate of these transitions. When the crystal morphology does not change, it is assumed that crystallinity is maintained throughout the process. Here we report transformation between polymorphs of ZnCl₂(1,3-diethylimidazole-2-thione)₂ which are sufficiently slow to allow unambiguous assignment of single crystal to single crystal transformation with shape preservation proceeding through an amorphous intermediate phase. This result fundamentally challenges the commonly accepted views of polymorphic phase transition mechanisms.

Emerging organic light‐emitting devices, such as light‐emitting electrochemical cells (LECs), offer a multitude of advantages but currently suffer from that most efficient phosphorescent emitters are based on expensive and rare metals. Herein, it is demonstrated that a rare metal‐free salt, bis(benzyltriphenylphosphonium)tetrabromidomanganate(II) ([Ph₃PBn]₂[MnBr₄]), can function as the phosphorescent emitter in an LEC, and that a careful device design results in the fact that such a rare metal‐free phosphorescent LEC delivers broadband white emission with a high color rendering index (CRI) of 89. It is further shown that broadband emission is effectuated by an electric‐field‐driven structural transformation of the original green‐light emitter structure into a red‐emitting structure.

Albeit tris(8‐hydroxyquinolinato) aluminum (Alq₃) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand‐centered states, the use of metal‐free 8‐hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8‐hydroxyquinolinium cations into a solid rigid network with appropriate counter‐anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as π‐stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue‐green (488 nm). Time‐dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long‐lived S₁ level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq₃ and related materials, both as solids and thin films with quantum yields (QYs) up to 40–50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 °C.