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.

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.

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.

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.

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.

Cellular uptake and biocompatibility of bismuth ferrite harmonic advanced nanoparticles.

Bismuth Ferrite (BFO) nanoparticles (BFO-NP) display interesting optical (nonlinear response) and magnetic properties which make them amenable for bio-oriented diagnostic applications as intra- and extra membrane contrast agents. Due to the relatively recent availability of this material in well dispersed nanometric form, its biocompatibility was not known to date. In this study, we present a thorough assessment of the effects of in vitro exposure of human adenocarcinoma (A549), lung squamous carcinoma (NCI-H520), and acute monocytic leukemia (THP-1) cell lines to uncoated and poly(ethylene glycol)-coated BFO-NP in the form of cytotoxicity, haemolytic response and biocompatibility. Our results support the attractiveness of the functional-BFO towards biomedical applications focused on advanced diagnostic imaging. FROM THE CLINICAL EDITOR: Bismuth Ferrite nanoparticles (BFO-NP) have been recently successfully introduced as photodynamic tools and imaging probes. However, how these nanoparticles interact with various cells at the cellular level remains poorly understood. In this study, the authors performed in vitro experiments to assess the effects of uncoated and PEG-coated BFO-NP in the form of cytotoxicity, haemolytic response and biocompatibility.

Anomalous trapped exciton and d-f emission in Sr4Al14O25:Eu2+.

The photoluminescence and time-resolved emission for Eu(2+) in Sr4Al14O25 has been investigated in the temperature range 4 to 500 K. The Eu(2+) emission changes in a peculiar way with temperature. At low temperature two emission bands are observed at 490 and 425 nm, which are attributed to emission from Eu(2+) on the 7- and 10-coordinated sites. Upon raising the temperature, an unexpectedly large blue shift to 400 nm is observed for the 425 nm emission band. To explain these observations, the 400 and 425 nm emission bands are assigned to d-f and trapped exciton emission, for Eu(2+) on the 10-coordinated site. The trapped exciton emission is characterized by a short (0.5 µs) decay time. The temperature dependence of the emission is explained by a configurational coordinate diagram in which the Eu(2+) trapped exciton state is at a slightly lower energy than the lowest energy 4f(6)5d state. Upon raising the temperature, the 4f(6)5d state is thermally populated and emission from this state is observed, and because of the smaller lattice relaxation (smaller Stokes shift), a large blue shift from 425 to 400 nm is observed.

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.

Solid state complex chemistry: formation, structure, and properties of homoleptic tetracyanamidogermanates RbRE[Ge(CN2)4] (RE = La, Pr, Nd, Gd).

Tetracyanamidometallates with the general formula RbRE[T(CN2)4] (RE = La, Pr, Nd, Gd; T = Si, Ge) were prepared by solid state metathesis reactions starting from stoichiometric mixtures of RECl3, A2[TF6], and Li2(CN2). Reactions were studied by differential thermal analysis that showed ignition temperatures between 360 and 390 °C for the formation of RbGd[T(CN2)4] with T = Si and Ge. The powder diffraction patterns of RbRE[Ge(CN2)4] were indexed isotypically to the already known RbRE[Si(CN2)4] compound. IR spectra of RbLa[Ge(CN2)4] were measured and compared with those of RbLa[Si(CN2)4]. (73)Ge, (87)Rb, and (139)La solid state NMR measurements and density functional theory calculations were used to verify the novel homoleptic [Ge(CN2)4](4-) ion. Luminescence properties of Eu(3+), Ce(3+), and Tb(3+) doped samples are reported.

Luminescence and luminescence quenching in Gd3(Ga,Al)5O12 scintillators doped with Ce3+.

The optical properties of gadolinium gallium aluminum garnet, Gd3(Ga,Al)5O12, doped with Ce(3+) are investigated as a function of the Ga/Al ratio, aimed at an improved understanding of the energy flow and luminescence quenching in these materials. A decrease of both the crystal field strength and band gap with increasing content of Ga(3+) is observed and explained by the geometrical influence of Ga(3+) on the crystal field splitting of the 5d level in line with theoretical work of Muñoz-García et al. ( uñoz-García, A. B.; Seijo, L. Phys. Rev. B 2010, 82, 184118 ). Thermal quenching results in shorter decay times as well as reduced emission intensities for all samples in the temperature range from 100 to 500 K. An activation energy for emission quenching is calculated from the data. The band gap of the host is measured upon Ga substitution and the decrease in band gap is related to Ga(3+) substitution into tetrahedral sites after all octahedral sites are occupied in the garnet material. Based on the change in band gap and crystal field splitting, band diagrams can be constructed explaining the low thermal quenching temperatures in the samples with high Ga content. The highest luminescence intensity is found for Gd3(Ga,Al)5O12 with 40% of Al(3+) replaced by Ga(3+).

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.

Luminescence and energy transfer in Lu3Al5O12 scintillators co-doped with Ce3+ and Tb3+.

Lu(3)Al(5)O(12) (LuAG) doped with Ce(3+) is a promising scintillator material with a high density and a fast response time. The light output under X-ray or γ-ray excitation is, however, well below the theoretical limit. In this paper the influence of codoping with Tb(3+) is investigated with the aim to increase the light output. High resolution spectra of singly doped LuAG (with Ce(3+) or Tb(3+)) are reported and provide insight into the energy level structure of the two ions in LuAG. For Ce(3+) zero-phonon lines and vibronic structure are observed for the two lowest energy 5d bands and the Stokes' shift (2 350 cm(-1)) and Huang-Rhys coupling parameter (S = 9) have been determined. Tb(3+) 4f-5d transitions to the high spin (HS) and low spin (LS) states are observed (including a zero-phonon line and vibrational structure for the high spin state). The HS-LS splitting of 5400 cm(-1) is smaller than usually observed and is explained by a reduction of the 5d-4f exchange coupling parameter J by covalency. Upon replacing the smaller Lu(3+) ion with the larger Tb(3+) ion, the crystal field splitting for the lowest 5d states increases, causing the lowest 5d state to shift below the (5)D(4) state of Tb(3+) and allowing for efficient energy transfer from Tb(3+) to Ce(3+) down to the lowest temperatures. Luminescence decay measurements confirm efficient energy transfer from Tb(3+) to Ce(3+) and provide a qualitative understanding of the energy transfer process. Co-doping with Tb(3+) does not result in the desired increase in light output, and an explanation based on electron trapping in defects is discussed.

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.

Synthesis and properties of tetracyanamidosilicates ARE[Si(CN2)4].

Tetracyanamidosilicates of the type ARE[Si(CN(2))(4)] with A = K, Rb, and Cs and RE = Y and La-Lu have been prepared by a solid-state metathesis reaction. The potassium compounds with RE = La-Gd crystallize orthorhombically in the space group P2(1)2(1)2. Rubidium as well as cesium compounds crystallize tetragonally in the space group I4. The luminescent properties of ARE[Si(CN(2))(4)]:Ln compounds with RE = Y, La, and Gd doped with 5 mol % Ln = Ce, Eu, or Tb were investigated. Temperature-dependent magnetic susceptibilities were measured for KGd[Si(CN(2))(4)]. The value of the magnetic moment is 7.3 mu(B)/Gd(3+) ion, which is in line with the expected value for the [Xe]4f(7) configuration of Gd(3+).

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.

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.

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.