Abstract Despite the significance of H 2 O 2 -metal adducts in catalysis, materials science and biotechnology, the nature of the interactions between H 2 O 2 and metal cations remains elusive and ...debatable. This is primarily due to the extremely weak coordinating ability of H 2 O 2 , which poses challenges in characterizing and understanding the specific nature of these interactions. Herein, we present an approach to obtain H 2 O 2 –metal complexes that employs neat H 2 O 2 as both solvent and ligand. SnCl 4 effectively binds H 2 O 2 , forming a SnCl 4 (H 2 O 2 ) 2 complex, as confirmed by 119 Sn and 17 O NMR spectroscopy. Crystalline adducts, SnCl 4 (H 2 O 2 ) 2 ·H 2 O 2 ·18-crown-6 and 2SnCl 4 (H 2 O 2 )(H 2 O)·18-crown-6, are isolated and characterized by X-ray diffraction, providing the complete characterization of the hydrogen bonding of H 2 O 2 ligands including geometric parameters and energy values. DFT analysis reveals the synergy between a coordinative bond of H 2 O 2 with metal cation and its hydrogen bonding with a second coordination sphere. This synergism of primary and secondary interactions might be a key to understanding H 2 O 2 reactivity in biological systems.
A series of fluorochlorozirconate glasses doped with manganese ions is synthesized and investigated as possible red‐emitting phosphors in comparison with conventional green‐emitting fluorozirconate ...glasses doped with Mn2+. It is found that the replacement of fluorine by chlorine ions results in broadening and a long‐wavelength shift of the manganese luminescence band into the red region (peaked at 615 nm) although the emission spectrum still has some contribution of the green sub‐band. It turns out also that decay kinetics of luminescence from fluorochlorozirconate glasses becomes nonexponential in contrast to single‐exponential decay observed for green luminescence from Mn2+‐doped fluorozirconate glasses. The observation of two emission components in the luminescence spectrum of fluorochlorozirconate glasses is interpreted as being due to the presence of two Mn2+ emission centers in different local environments. The presence of 2+ valence states of manganese ions in both types of glasses is confirmed by recording X‐ray absorption near edge structure (XANES) spectra at Mn L2,3 edge. Substitution of F− by Cl− ions in anion sites neighboring to Mn2+, leads to a significant rearrangement of the local environment of Mn2+ ions, which results in the long‐wavelength shift of Mn2+ emission spectrum.
Fluorochlorozirconate glasses doped with manganese ions are proposed as broadband green–red‐emitting phosphors for white light‐emitting diodes (LEDs). The replacement of F− by Cl− ions in fluorozirconate glass host results in the shift of Mn2+ emission spectrum caused by the 4T1–6A1 transition from the green region (λmax ≈ 545 nm) to the red one (λmax ≈ 615 nm).
The luminescence properties of ceramic phosphors based on two spinel hosts MgAl2O4 and ZnAl2O4 doped with manganese ions have been studied. It has been found that the spectral properties of these ...phosphors can be strongly varied by changing synthesis conditions. Both types of doped ceramic spinel can serve as efficient Mn2+ green-emitting phosphors having peak emissions at 525 and 510 nm, respectively. Mn-doped MgAl2O4 spinel can also be prepared as an efficient Mn4+ red-emitting phosphor having peak emission at ~651 nm by using specific temperatures of heat treatment in air. It has also been shown that the conversion of Mn2+ to Mn4+ and viсe versa, as well as the coexistence of Mn2+ green and Mn4+ red emissions, can be accomplished by properly chosen annealing conditions of the same initially synthesized MgAl2O4:Mn sample. Manganese doped MgAl2O4 spinel with an optimal intensity ratio of green and red emissions can be a promising single-phase bicolor phosphor suitable for the development of warm white phosphor-converted LED lamps. On the other hand, it has been determined that perfectly normal ZnAl2O4 spinel cannot be doped with Mn4+ ions in contrast to partially inverse MgAl2O4 spinel. However, ZnAl2O4 samples unintentionally doped with impurity Cr3+ ions show emission spectra in the far-red region with well pronounced R, N and vibronic lines of Cr3+ luminescence due to the perfect normal spinel structure of synthesized ZnAl2O4 ceramics. Also, by partially substituting Al3+ cations for Mg2+ in ZnAl2O4 there is an opportunity to obtain Mn4+ doped or Mn4+/Cr3+ codoped far-red emitting phosphors which can be suitable for indoor plant growth lighting sources.
Ceramic samples of two multi-cation fluoride compositions, namely Na3CaMg3AlF14 doped with Ce3+ or Eu2+ and KCaAl2F9 doped with Eu2+, have been synthesized using a conventional solid-state reaction ...method. The XRD analysis shows that the new polymorphic modification of Na3CaMg3AlF14 with the cubic A2B2X7 pyrochlore crystal structure (space group Fd3‾m, lattice parameter 10.172 Å) has been obtained. This conclusion is confirmed with the simulation of the XRD pattern for the cubic pyrochlore structure by introducing random occupation of Na+ and Ca2+ ions at the A-type sites as well as Mg2+ and Al3+ ions at the B-type sites in the structure of rhombohedral Na3CaMg3AlF14. It has been shown that doping of the Na3CaMg3AlF14 pyrochlore matrix with Ce3+ ions creates several Ce3+ optical centers with different spectral and decay properties of 5d-4f luminescence. In contrast to that, doping with Eu2+ ions creates a single optical center by the substitution for the Na/Ca A-type site in the cubic Na3CaMg3AlF14 pyrochlore structure. In Eu2+-doped Na3CaMg3AlF14, the Eu2+ emission band caused by the interconfigurational 4f65d – 4f7 transition has a rather narrow width (FWHM = 29 nm) which is considerably less than that observed in Eu2+-doped KCaAl2F9 (FWHM = 44 nm) in which the emission band is broadened due to the existence of two types of sites for doping Eu2+ ions. The Eu2+ ions doped into Na3CaMg3AlF14 and KCaAl2F9 hosts emit not only broad-band 4f65d – 4f7 luminescence but also a narrow-line 4f7 – 4f7 (6P7/2 - 8S7/2) emission which is not observed under excitation to the lowest-energy 4f65d state. It has been shown that both Na3CaMg3AlF14:Eu2+ and KCaAl2F9:Eu2+ demonstrate a rather good thermal stability of luminescence with thermal quenching temperature T1/2 equal to 504 and 573 K, respectively.
•Novel cubic polymorphic modification of Na3CaMg3AlF14 pyrochlore has been synthesized.•Eu2+ ions create a single luminescence center in the cubic Na3CaMg3AlF14 pyrochlore.•In the Na3CaMg3AlF14 host Eu2+ ions show both 4f65d-4f7 and 6P7/2-8S7/2 luminescence.•4f65d-4f7 luminescence of Eu2+ doped into Na3CaMg3AlF14 has high thermal stability.•Ce3+ ions create several luminescence centers in the cubic Na3CaMg3AlF14 structure.
Ceramic samples of lithium aluminates doped with manganese ions have been synthesized by a solid-state reaction method. The ceramics sintered at temperatures of 1000, 1100, 1200 or 1300 °C for 4 h in ...air are identified as LiAl5O8 compounds belonging to a spinel-like crystal structure with the P4132 space group. Nonetheless, ceramic compositions obtained by annealing at temperatures 1000, 1100 or 1200 °C have larger lattice parameters than that of a LiAl5O8 single crystal and are considered as metastable LiAl5O8 phases having partial disorder for the occupation of two inequivalent octahedral sites by Li+ and Al3+ ions, i.e. possessing Li - Al inversion. Such Mn doped disordered compositions show typical Mn4+ red luminescence with an emission peak at ∼662 nm. The charge compensation of Mn4+ replacing Al3+ ions in octahedral sites is achieved by Li+ ions entering some adjacent Al3+ sites due to inversion. On the other hand, annealing at a higher temperature (1300 °C) or prolonged (170 h) annealing at a lower temperature (1100 °C) leads to complete ordering of Li+ and Al3+ in ratio 1:3 at different octahedral sites in the LiAl5O8 structure in which Mn4+ luminescence is not observed due to the lack of a charge compensation mechanism. Doping Mn ions in such an ordered structure are realized in di- and trivalent states causing green and far-red luminescence, respectively. Additional annealing of the mixtures of the Mn-doped ordered LiAl5O8 composition and Li2CO3 at 1300 °C in air results in the production of phosphors which again show intense Mn4+ red luminescence and have the spinel-like crystal structure with the Fd3‾m space group due to random occupation of cationic sites by Li+ and Al3+ ions.
•Partially disordered LiAl5O8 structure (P4132) is formed due to Li–Al inversion.•Completely ordered LiAl5O8 structure (P4132) is formed under prolonged annealing.•Random cation distribution creates fully disordered LiAl5O8 spinel structure (Fd3‾m).•Red luminescence of doping Mn4+ ions is observed only in disordered LiAl5O8 hosts.•Mn doped completely ordered LiAl5O8 is characterized by Mn2+ and Mn3+ luminescence.
Synthesis of anhydrous cerium tetrafluoride Brekhovskikh, Maria N.; Vaimugin, Leonid A.; Moiseeva, Liudmila V. ...
Journal of fluorine chemistry,
April 2024, 2024-04-00, Letnik:
275
Journal Article
Recenzirano
•A procedure for the synthesis of the anhydrous CeF4 by the reaction between CeF3 and XeF2 was proposed.•Characterization of the forming CeF4 was carried out by XRD, FTIR, 19F NMR and ...thermogravimetry.•The anhydrous CeF4 was found to undergo hydration when exposed to air.•An approximate formula CeF4•0.2H2O*0.7H2O for the crystalline hydrate, formed after exposure to air, was proposed.
By reacting CeF3 with XeF2 the anhydrous CeF4 was synthesized and studied by XRD, SEM, FTIR, 19F NMR spectrometry and thermogravimetry. It was found that CeF4 undergoes hydration upon keeping in air forming the crystalline hydrate with the approximate formula CeF4•0.2H2O*0.7H2O. Water molecules both enter the coordination sphere of cerium and form crystalline hydrates with cerium(IV) fluoride due to OH…F hydrogen bonds in the crystal lattice.
Display omitted
Display omitted
The nuclear quadrupole resonance (NQR) spectroscopy was used to control the comparative purity of three SnCl4 samples subjected to successive stages of deep purification. The results ...showed that at 77 K the samples were identical in purity degree due to the ‘freezing’ of impurities into a separate fraction not affecting the perfection of the SnCl4 crystal lattice. The results of relaxation measurements suggest that paramagnetic impurity atoms (Fe and Cr) contained in the samples in small amounts might be embedded into the crystal lattice causing extremely long spin–spin relaxation time.
Display omitted
The relative content of the perovskite phase in two CsSnI3 samples (of 99.900 and 99.999 wt% SnI2 and 99.999 wt% CsI purity) was estimated using 127I NQR. The results showed that both ...samples contained the non-perovskite orthorhombic phase as an admixture. In the sample of higher purity (99.999 wt%) its content was insignificant – only trace amounts could be observed at 77 K, whereas at room temperature the presence of the non-perovskite phase was not revealed. However, in the sample of 99.900 wt% purity the content of the non-perovskite phase has reached at least a third of the sample amount, which is due to the probable crystallization of the non-perovskite phase on impurities.
Display omitted
Fluorozirconate glass doped with K2MnF6 was produced to obtain a red-emitting phosphor, and K2MnF6 was synthesized according to a specially developed procedure using xenon difluoride. ...The luminescence spectrum exhibited a band at 550 nm attributed to Mn2+, and the absorption spectra belonged to Mn2+ and Mn3+ ions, which were formed due to the reduction of Mn4+ ions.
