Thermal deprotonation and condensation of melamine in the presence of indium(III)chloride.

The thermal condensation of melamine into molecules melam, melem, and the one-dimensional polymer melon has already been reported. An interesting question arises about the impact of other compounds being present in this process of thermal conversion. The solid-state reaction of C3N6H6 with InCl3 leads to a novel compound featuring deprotonated melam units in a supramolecular assembly, based on the [C12N20H8]4- anion that is interconnected in the structure via N-In-N bonding. The reaction pathway of the formation of this compound is investigated by thermal analysis and the crystal structure of unique (NH4)[(InCl2)3(C12N20H8)]·â…”[InCl3(NH3)] is reported as well as its photoluminescence properties.

The luminescent semiconductor Pb7I6(CN2)4.

The development of new compounds in the domain of metal dinitridocarbonates is most efficiently performed via solid-state metathesis or simply by addition reactions. Our discovery of Pb7I6(CN2)4 is the result of a solid-state reaction of PbCN2 with PbI2 at 420 °C. Its crystal structure was solved and refined from X-ray diffraction data based on a single crystal with the space group P63/mmc. The crystal structure is based on a network of lead tetrahedra, lead trigonal bipyramids and lead octahedra interconnected by [NCN]2- and iodide. Properties of the material were investigated by diffuse reflection measurement, photoluminescence measurements, and electronic band structure calculations demonstrating that this material is a semiconductor.

Novel bandpass filter for far UV-C emitting radiation sources.

Disinfection with far UV-C radiation (<230 nm) is an effective method to inactivate harmful microorganisms like the SARS-CoV2 virus. Due to the stronger absorption than regular UV-C radiation (254 nm) and hence limited penetration into human tissues, it has the promise of enabling disinfection in occupied spaces. The best far-UV sources so far are discharge lamps based on the KrCl* excimer discharge peaking at 222 nm, however they produce longer wavelength radiation as a by-product. In current KrCl* excimer lamps usually a dichroic filter is used to suppress these undesired longer wavelengths. A phosphor-based filter is an alternative which is cheaper and easier to apply. This paper describes the results of our exploration of this opportunity. Various compounds were synthesized and characterized to find a replacement for the dichroic filter. It was found that Bi3+-doped ortho-borates with the pseudo-vaterite crystal structure exhibit the best absorption spectrum i.e. high transmission around 222 nm and strong absorption in the 235-280 nm range. Y0.24Lu0.75Bi0.01BO3 showed the best absorption spectrum in the UV-C. To suppress the unwanted Bi3+ emission (UV-B), the excitation energy can be transferred to a co-dopant. Ho3+ turned out to be the best co-dopant, and Ho0.24Lu0.75Bi0.01BO3 appeared to be the best overall candidate for the phosphor filter material. A suitable formulation for a coating suspension containing this material was found, and quite homogeneous coatings were achieved. The efficiency of these filter layers was investigated and the results in terms of exposure limit increase i.e. gain factor vs. no filter were compared with the dichroic filter. We achieved a gain factor for the Ho3+ containing sample of up to 2.33, i.e. not as good as that of the dichroic filter (∼4.6), but a very relevant improvement, making Ho0.24Lu0.75Bi0.01BO3 an interesting material for a cost-effective filter for KrCl* far UV-C lamps.

Preparation, photoluminescence and excited state properties of the homoleptic cluster cation [(W6I8)(CH3CN)6]4.

Solvated tungsten iodide cluster compounds are presented with the homoleptic cluster cation [(W6I8)(CH3CN)6]4+ and the heteroleptic [(W6I8)I(CH3CN)5]3+, synthesized from W6I22 in acetonitrile. Crystal structures were solved and refined on deep red single-crystals of [(W6I8)(CH3CN)6](I3)(BF4)3·H2O, [(W6I8)I(CH3CN)5](I3)2(BF4), and on a yellow single-crystal of [W6I8(CH3CN)6](BF4)4·2(CH3CN) on the basis of X-ray diffraction data. The structure of the homoleptic [(W6I8)(CH3CN)6]4+ cluster is based on the octahedral [W6I8]4+ tungsten iodide cluster core, coordinated by six apical acetonitrile ligands. The electron localisation function of [(W6I8)(CH3CN)6]4+ is calculated and solid-state photoluminescence and its temperature depedence are reported. Additionally, photoluminescence and transient absorption measurements in acetonitrile are shown. Results of the obtained data are compared to compounds containing [(M6I8)I6]2- and [(M6I8)L6]2- (M = Mo or W; L = ligand) clusters.

On the Quantum Yield Determination of UV Emitting Up-Converters.

This work deals with the determination of the external quantum yield of some selected inorganic up-conversion materials, which are able to convert blue light, as typically emitted using blue (In,Ga)N LEDs, into UV radiation. Recently, these materials have drawn tremendous attention due to their potential application in antimicrobial coatings of surfaces. To judge the viability of this approach to reduce the density of germs onto arbitrary surfaces upon indoor or outdoor illumination, the quantum efficiency for the conversion of blue light into UV is of large interest. We found that the quantum efficiency is between about 0.1% and 1%, which might be good enough if the illumination of the respective surface is performed for several hours. Then, a relevant reduction of the number of active microorganisms per area can be achieved.

Extraordinary intense blue Tl+ lone-pair photoluminescence from thallium(I) chloride hydroborate Tl3Cl[B12H12].

Microcrystalline powder of previously unknown thallium(I) chloride hydroborate Tl3Cl[B12H12] was obtained through the reaction of thallium(I) oxocarbonate Tl2[CO3] with an aqueous solution of (H3O)2[B12H12] in the presence of chloride anions. Tl3Cl[B12H12] crystallises in a primitive, orthorhombic lattice with the space group Pnma (a = 835.189(7) pm, b = 970.132(8) pm and c = 1597.912(12) pm for Z = 4) showing a distorted hexagonal anti-perovskite type arrangement of the ions. The structure features two thallium sites with mixed coordination spheres consisting of borate related hydrogen atoms and chloride anions with coordination numbers of eleven and thirteen. Tl3Cl[B12H12] shows strong excitation bands at 240 and 260 nm attributed to the 1S0 → 3P2 and 1S0 → 3P1 interconfigurational transitions of the Tl+ 6s2 cations, respectively. The emission spectrum at 300 K upon VUV excitation exhibits a broad band at 440 nm with a quantum efficiency of 41%. In addition, temperature-dependent emission spectra, colour points, reflectance, decay time, thermal quenching curve and radioluminescence spectra for Tl3Cl[B12H12] were determined.

UV emitting nanoparticles enhance the effect of ionizing radiation in 3D lung cancer spheroids.

PURPOSE: Radiation therapy for cancer is limited by damage to surrounding normal tissues, and failure to completely eradicate a tumor. This study investigated a novel radiosensitizer, composed of lutetium phosphate nanoparticles doped with 1% praseodymium and 1.5% neodymium cations (LuPO4:Pr3+,Nd3+). During X-ray exposure, the particles emit UVC photons (200-280 nm), resulting in increased tumor cell death, by oxygen-independent UVC-induced damage. METHODS AND MATERIALS: Specially designed LuPO4:Pr3+,Nd3+ nanoscintillator particles were characterized by dynamic light scattering, TEM and emission spectroscopy upon excitation. Cell death was determined by reduction in tumor spheroid growth over a 3-week period using a 3 D A549 lung cancer model. Cell cycle was evaluated by flow cytometry and cell death pathways were assessed by Annexin V/PI stain as well as quantify apoptotic bodies. RESULTS: Lung cancer cells expressed no long-term or nonspecific toxicity when incubated with LuPO4:Pr3+,Nd3+ nanoscintillators. In contrast, there was significant growth inhibition of cell spheres treated with 2.5 mg/ml LuPO4:Pr3+,Nd3+ in combination with ionizing radiation (4 or 8 Gy X-ray), compared to radiation alone. Homogeneous distribution of small NPs throughout the entire sphere resulted in more pronounced lethality and growth inhibition, compared to particle distribution limited to the outer cell layers. Growth inhibition after the combined treatment was caused by necrosis, apoptosis and G2/M cell cycle arrest. CONCLUSIONS: Newly designed UVC-emitting nanoscintillators (LuPO4:Pr3+,Nd3+) in combination with ionizing radiation cause tumorsphere growth inhibition by inducing cell cycle arrest, apoptosis and necrosis. UVC-emitting nanoparticles offer a promising new strategy for enhancing local tumor response to ionizing radiation treatment.

On the crystal structure and optical spectroscopy of rare earth comprising quaternary tungstates Li3Ba2RE3(WO4)8 (RE = La-Nd, Sm-Ho).

The quaternary tungstates Li3Ba2RE3(WO4)8 (RE = La-Nd, Sm-Ho) were obtained by a ceramic synthesis route and were characterized by powder and single crystal X-ray diffraction. The structures of Li3Ba2Pr3(WO4)8 and Li3Ba2Tb3(WO4)8 were refined from single crystal diffractometer data: RbLiBi2(MoO4)4 type, space group C2/c, a = 528.57(2), b = 1292.39(6), c = 1934.80(10) pm, ß = 91.522(4)°, 2151 F2 values, 108 parameters for Li3Ba2Pr3(WO4)8 and a = 520.54(2), b = 1272.03(6), c = 1918.85(10) pm, ß = 91.948(4)°, 2020 F2 values, 108 variables for Li3Ba2Tb3(WO4)8. Striking polyhedral building units in these tungstates are WO4 tetrahedra and LiO6 octahedra, while the mixed occupied site and the barium atoms have higher coordination numbers, i.e. RE/Li@O8 and Ba@O10. In addition to the powder quality assessment by means of reflection spectroscopy, the synthesized samples were studied for their suitability as a scintillator material. Therefore, X-ray excited luminescence measurements where performed. Apart from Li3Ba2Ce3(WO4)8 and Li3Ba2Nd3(WO4)8, all compounds show strong emission under X-ray irradiation. Li3Ba2La3(WO4)8 and Li3Ba2Gd3(WO4)8 show blue CT luminescence caused by tungstate units, while the other samples show typical and multiple lines due to well known [Xe]4fn → [Xe]4fn transitions.

Watt-level europium laser at 703 nm.

We report on a watt-level highly efficient europium laser operating at the ${^5{\rm D}_0 \to {^7}{\rm F}_4}$ transition. It is based on the stoichiometric ${\rm KEu}{({\rm WO}_4)_2}$ crystal. Under pumping by a green laser at 532.1 nm, the ${\rm KEu}{({\rm WO}_4)_2}$ laser generated a maximum peak output power of 1.11 W at ${\sim}{703}\;{\rm nm}$ with a slope efficiency of 43.2% and a linear polarization ($E\|\;{N_m}$). A laser threshold as low as 64 mW was achieved. True continuous-wave operation was demonstrated. The polarized emission properties of monoclinic ${\rm KEu}{({\rm WO}_4)_2}$ were determined.

Structure, polymorphism and luminescence of cyanate iodides MI(OCN) (M = Ba, Eu, and Sr).

A series of new compounds MI(OCN) were prepared from the mixtures of MI2 and K(OCN) (M = Sr, Eu or Ba) by solid-state reactions that were controlled by differential scanning calorimetry (DSC) and differential thermal analysis (DTA) techniques. The presence of two phases is highlighted for BaI(OCN) which crystallizes in the Pnma (α-BaI(OCN)) and Cmcm (ß-BaI(OCN)) space groups. The SrI(OCN), EuI(OCN) and ß-BaI(OCN) compounds crystallize in the same orthorhombic Cmcm space group and the structure consists of a layered arrangement of [M2I2]2+ blocks separated by single layers of cyanate ions that are found to be related to the Sillén-type structure. The polymorphism of BaI(OCN) was also observed by analyzing the infrared (IR) spectra. This analysis showed for ß-BaI(OCN) splitting bands, which were ascribed to the presence of more than one resonant cyanate form that can be induced by the dynamical disorder of OCN units. In contrast, the α-BaI(OCN) vibration modes suppose the existence of one cyanate form that adopts a defined orientation. The SrI(OCN) and BaI(OCN) compounds were doped with Eu2+. The luminescence spectra recorded under excitation at 340 and 350 nm revealed a blue emission of Eu2+ at 431 nm for the ß-BaI(OCN) and SrI(OCN) phases and at 427 nm for the α-BaI(OCN) phase that was ascribed to the 4f65d1→8S7/2 (4f7) transition.

Energy transfer in supramolecular [Crypt-RE]-[W6I14] solids.

Photophysical properties of tungsten iodides with the [W6I14]2- cluster core have been described with respect to phosphorescence and phosphorescence quenching by molecular oxygen. This process involves energy transfer from excited triplet states of the cluster onto molecular oxygen. In the present study we investigate deactivation channels of exited triplet states of the [W6I14]2- cluster towards rare earth ions. For this purpose, we synthesized several supramolecular assemblies made of [W6I14]2- clusters and metal cryptates and investigated their crystal structures and photophysical properties. UV/Vis photoexcitation of solid [Crypt-A]-[W6I14] (A = alkaline metal) and [Crypt-RE]-[W6I14] revealed phosphorescence of the cluster, respectively of the photophysically active rare earth metal (RE) center. A cluster to cryptate energy transfer is proven with a photophysically active rare earth ion by the emission of Yb3+ at 977 nm (2F5/2-2F7/2) and Nd3+ 1072 nm (4F3/2-4I11/2). These results show that an effective excitation of near-infrared-emitting rare earth ions is possible under excitation up to 550 nm with [Crypt-RE]-[W6I14] assemblies.

Photodynamic properties of tungsten iodide clusters incorporated into silicone: A2[M6I8L6]@silicone.

The light-induced antibacterial and antifungal properties of A2[M6I8L6] with M = Mo and W, A = organic cation, L = ligand have been studied. The photoactive compounds (TBA)2[W6I8(C7H7SO3)6] and (TBA)2[W6I8(COOCF3)6] have been incorporated into a permeable silicone matrix and were measured for their application in the decomposition of multi-resistant bioactive species (hospital germs) such as S. aureus and P. aeruginosa as well as fungi. In addition, we present a new high volume synthesis route for these types of cluster compounds departing from the soluble compound W6I22.

UVC-Emitting LuPO4:Pr3+ Nanoparticles Decrease Radiation Resistance of Hypoxic Cancer Cells.

Radiation-resistant hypoxic tumor areas continue to present a major limitation for successful tumor treatment. To overcome this radiation resistance, an oxygen-independent treatment is proposed using UVC-emitting LuPO4:Pr3+ nanoparticles (NPs) and X rays. The uptake of the NPs as well as their effect on cell proliferation was investigated on A549 lung cancer cells by using inverted time-lapse microscopy and transmission electron microscopy. Furthermore, cytotoxicity of the combined treatment of X rays and LuPO4:Pr3+ NPs was assessed under normoxic and hypoxic conditions using the colony formation assay. Transmission electron microscopy (TEM) images showed no NP uptake after 3 h, whereas after 24 h incubation an uptake of NPs was documented. LuPO4:Pr3+ NPs alone caused a concentration-independent cell growth delay within the first 60 h of incubation. The combined treatment with UVC-emitting NPs and X rays reduced the radiation resistance of hypoxic cells by a factor of two to the level of cells under normoxic condition. LuPO4:Pr3+ NPs cause an early growth delay but no cytotoxicity for the tested concentration. The combination of these NPs with X rays increases cytotoxicity of normoxic and hypoxic cancer cells. Hypoxic cells become sensitized to normoxic cell levels.

Synthesis, structure and properties of a calcium oxonitridosilicate phosphor showing green or red luminescence upon doping with Eu2+ or Ce3.

The phase LixCa16-xSi17N32-xO2+x was synthesized by solid-state metathesis at 1050 °C in weld-sealed niobium ampoules. The crystal structure was solved from powder X-ray diffraction data in the space group F4[combining macron]3m (a = 14.7391(1) Å, Z = 4); it is closely related to the previously reported structure of Ca16Si17N34. The structure of LixCa16-xSi17N32-xO2+x is based on a complex network of [SiN4] tetrahedra with interstitial voids filled by Ca ions, partially substituted by Li. This Li substitution is charge-compensated by replacement of N by O in the structure. Theoretical calculations confirm that the unit cell volume decreases with increasing stoichiometric factor x. Europium doped samples of this compound show intense Eu2+ emission at 536 nm on excitation with near-UV or blue radiation at 350-480 nm. Ce3+ doping yields orange to red emission with two broad emission bands at 600 and 665 nm.

Red-emitting K3HF2WO2F4:Mn4+ for application in warm-white phosphor-converted LEDs - optical properties and magnetic resonance characterization.

We report novel efficient Mn4+ phosphors of composition K3HF2MO2F4:Mn4+ (M = Mo, W) containing [HF2]- and octahedral [MO2F4]2- building units. The phosphor exhibits strong absorption at 450 nm and an external quantum yield of 90%. K3HF2WO2F4:0.01Mn4+ provides a sufficiently high quenching temperature T1/2 of about 400 K and is applicable as a converter for (In,Ga)N LEDs. The EPR spectrum is consistent with the presence of a MnF62- species at giso = 1.983. 19F MAS NMR results confirm the 2 : 1 ratio of the metal-bound fluoride species to the hydrogen difluoride group as predicted from the chemical formula. There are two distinct M-bonded species in a 1 : 1 ratio, indicating that the W and Mo octahedra are exclusively of the MO2F42- type, with the two oxygen atoms in cis-position. Their extremely sharp 19F resonances indicate a fast, near-isotropic reorientational process at room temperature that is on the millisecond timescale. For the HF2- group, the 19F and 1H MAS NMR spinning sideband profiles reveal the geometry of a linear centrosymmetric three-spin system with an H-F bond distance of 1.14 Å.

On the sensitization of Eu3+ with Ce3+ and Tb3+ by composite structured Ca2LuHf2Al3O12 garnet phosphors for blue LED excitation.

This work deals with the photoluminescence of various composite structured Ca2LuHf2Al3O12 garnet type LED phosphors. It is well known that sensitization of Eu3+ with Ce3+ suffers from metal-to-metal charge transfer (MMCT) quenching. Spatial separation of the sensitizer and activator results in a reduced quenching mechanism and thus higher luminescence intensities, when Ce3+ is excited in the blue spectral range and transfers its energy to Eu3+. The phosphor particles were prepared via different synthesis techniques. The phase purity of the synthesized particles was determined by X-ray powder diffraction. Scanning electron microscopy images were obtained to study the particle morphology and composite formation. Photoluminescence properties were determined by recording the emission spectra, excitation spectra and diffuse reflectance spectra. Furthermore, the temperature dependent emission spectra and fluorescence lifetimes were recorded to compare thermal quenching and decay behavior of the samples. External quantum efficiencies (EQEs) were calculated to examine the MMCT quenching behavior. Since the EQE of Ca2LuHf2Al3O12:Ce3+,Tb3+,Eu3+ is lower than 1%, it could be demonstrated that the composite approach significantly increases the EQE due to the spatial separation of Ce3+ and Eu3+.

Properties Design: Prediction and Experimental Validation of the Luminescence Properties of a New EuII -Based Phosphor.

A theoretical model that allows to predict, for the first time, the luminescence properties of a new phosphor (BaSnSi3 O9 :Eu2+ ) is presented. The predicted emission wavelength, 488 nm with a 64 nm bandwidth, was confirmed by subsequent experimental work. The method consists in a multi-electron Hamiltonian parametrized from ab initio calculations. The luminescence properties of other similar compounds (i.e., BaHfSi3 O9 :Eu2+ and BaZrSi3 O9 :Eu2+ ), for which there is already experimental information, were also correctly reproduced.

Photoluminescence and energy transfer behavior of narrow band red light emitting Li3Ba2Tb3(MoO4)8:Eu3.

This work concerns the polycrystalline red emitting solid state compound Li3Ba2(Tb1-xEux)3(MoO4)8, from which a series of powder samples was prepared by a conventional solid-state reaction. The phase formation of the samples was investigated by X-ray diffraction which revealed the formation of a solid solution without a miscibility gap. Photoluminescence (PL) spectra and decay curves were recorded as a function of Tb3+ and Eu3+ concentration and temperature. It turned out that the external quantum efficiency of Eu3+ photoluminescence is between 30 and 80%, while the highest quantum yield is achieved for about 60% Tb3+. An increase of emission intensity can be realized by co-doping of Eu3+ and Tb3+. Moreover, the emission has a luminous efficacy of 275 lm Wopt-1 which is a distinct advantage over the widely applied Mn4+ activated fluorides. The time dependent photoluminescence as a function of Tb3+ concentration demonstrates the presence of an efficient energy transfer from Tb3+ to Eu3+. Temperature dependent PL measurements revealed that Li3Ba2(Tb1-xEux)3(MoO4)8 loses just 20% of PL efficiency up to 400 K. Therefore, the investigated phosphors are attractive for application in pcLEDs. It is finally demonstrated that the application of a Eu3+/Tb3+ co-doped ceramic disc is useful for the colour conversion of a blue emitting LED with a higher conversion rate compared to Li3Ba2(La1-xEux)3(MoO4)8.

Fabrication and characterization of UV-emitting nanoparticles as novel radiation sensitizers targeting hypoxic tumor cells.

Radiation therapy is one of the primary therapeutic techniques for treating cancer, administered to nearly two-thirds of all cancer patients. Although largely effective in killing cancer cells, radiation therapy, like other forms of cancer treatment, has difficulty dealing with hypoxic regions within solid tumors. The incomplete killing of cancer cells can lead to recurrence and relapse. The research presented here is investigating the enhancement of the efficacy of radiation therapy by using scintillating nanoparticles that emit UV photons. UV photons, with wavelengths between 230 nm and 280 nm, are able to inactivate cells due to their direct interaction with DNA, causing a variety of forms of damage. UV-emitting nanoparticles will enhance the treatment in two ways: first by generating UV photons in the immediate vicinity of cancer cells, leading to direct and oxygen-independent DNA damage, and second by down-converting the applied higher energy X-rays into softer X-rays and particles that are more efficiently absorbed in the targeted tumor region. The end result will be nanoparticles with a higher efficacy in the treatment of hypoxic cells in the tumor, filling an important, unmet clinical need. Our preliminary experiments show an increase in cell death using scintillating LuPO4:Pr nanoparticles over that achieved by the primary radiation alone. This work describes the fabrication of the nanoparticles, their physical characterization, and the spectroscopic characterization of the UV emission. The work also presents in vitro results that demonstrate an enhanced efficacy of cell killing with x-rays and a low unspecific toxicity of the nanoparticles.

A ligand substituted tungsten iodide cluster: luminescence vs. singlet oxygen production.

Octahedral tungsten iodide clusters equipped with apical ligands (L) are synthesized to implement substantial photophysical properties. The [W6I8(CF3COO)6]2- cluster reported herein is the first example of a family of ligand substituted [W6I8L6]2- clusters. Such compounds are expected to exhibit a rich photochemistry in which the apical ligands play a crucial role. The versatile solid state and solution phase photophysical properties of (TBA)2[W6I8(CF3COO)6] described herein parallel characteristics obtained in some photophysically active organic compounds, including a broad absorption in the UV/VIS region. Upon irradiation of this compound, a broad red emission is observed in the VIS/NIR region resulting from excited triplet states, and singlet oxygen (a1Δg) is generated in the presence of O2.