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.

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 by blue (In,Ga)N LEDs, into UV radiation. Recently, these materials draw 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. It turned out that the quantum efficiency is between about 0.1 and 1%, which be might 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.

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.

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 3D 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 non-specific 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. A 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 tumor sphere 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, β = 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, β = 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 (β-BaI(OCN)) space groups. The SrI(OCN), EuI(OCN) and β-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 β-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 β-BaI(OCN) and SrI(OCN) phases and at 427 nm for the α-BaI(OCN) phase that was ascribed to the 4f⁶5d¹→⁸S_7/2 (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.

The light-induced antibacterial and antifungal properties of A₂[M₆I₈L₆] with M = Mo and W, A = organic cation, L = ligand have been studied.

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 Li_xCa_16-xSi₁₇N_32-xO_2+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 Li_xCa_16-xSi₁₇N_32-xO_2+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

A novel efficient red-emitting Mn⁴⁺ phosphor of composition K₃HF₂MO₂F₄:Mn⁴⁺ (M = Mo, W).

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

Luminescence quenching by metal-to-metal charge transfer between Ce³⁺ and Eu³⁺ was reduced significantly by spatial separation of activator and sensitizer in core-shell like composite particles.

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.

Temperature dependent optical properties of red emitting Na3GaF6:Mn4+ as a color converter for warm white LEDs

This work presents and disentangles the temperature dependent optical properties of the red-emitting phosphor Na3GaF6:Mn4+. Moreover, crystal field and Racah parameters were investigated. It was proven that the material is suitable for the application in warm white LEDs due to its high quantum yield of about 83%, little thermal quenching of the photoluminescence up to 410 K, high lumen equivalent of about 220 lm/W, and strong absorption at 450 nm. In addition, different DFT approaches were used to investigate its band structure. The calculated data were compared to those obtained experimentally. Red phosphor spectra were calculated to evaluate the suitability of red line-emitting phosphors for the application in warm white emitting pcLEDs. Finally, warm white emitting LEDs comprising Na3GaF6:Mn4+ were constructed in order to show the potential of Na3GaF6:Mn4+ serving as a red component in phosphor blends for future warm white pcLEDs.

Na3GaF6 – A crystal chemical and solid state NMR spectroscopic study

Na3GaF6 and Na3GaF6:Mn4+ samples were obtained from NaNO3 and Ga(NO3)3·9H2O in hydrofluoric acid using K2MnF6 or NaMnO4 as manganese sources. The structure of Na3GaF6 was studied by single crystal X-ray diffraction at 90, 293, 440 and 500 K, confirming the monoclinic cryolite type structure, space group P21/c. The gallium atoms show slightly distorted octahedral coordination by fluorine atoms, similar to the Na1 atoms. Coordination number 8 is observed for Na2. Both sodium sites are clearly distinguished by 23Na MAS-NMR spectroscopy. Above 400 K the spectra reveal distinct chemical exchange effects, signifying sodium ion hopping between these two sites. At the same time static 19F NMR spectra indicate pronounced motional narrowing effects in this temperature region. The nearly invariant 69Ga MAS-NMR spectra suggest that any reorientational motion involving the GaF6 3− ions (if present) occurs with preservation of the center of mass of these octahedra.

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

The emission integral of efficient red emitting Li₃Ba₂Eu₃(MoO₄)₈ was strongly increased by partly substituting Eu³⁺ with Tb³⁺.

Superstructure formation in SrBa8[BN2]6 and EuBa8[BN2]6

X-ray pure samples of SrBa8[BN2]6 and EuBa8[BN2]6 were synthesized from appropriate amounts of binary nitrides (Sr3N2, Ba3N2 and BN in sealed niobium ampoules and EuN, Ba3N2 and BN in BN crucibles, respectively) at temperatures up to 1370 K. The structure of SrBa8[BN2]6 was refined from single crystal X-ray diffractometer data: Fd3[combining macron]m, a = 1595.1(1) pm, wR(F(2)) = 0.0515, 387 F(2) values and 21 variables. EuBa8[BN2]6 has a lattice parameter of 1595.00(9) pm. Both nitridoborates adopt a new 2 × 2 × 2 superstructure variant of the LiCa4[BN2]3 type, realized through ordering of vacancies and Sr(2+) and Eu(2+) cations, respectively. The structures of SrBa8[BN2]6 and LiCa4[BN2]3 are related by a group-subgroup scheme. The Sr(2+)/vacancy ordering leads to an asymmetric coordination (1 × Sr(2+) and 8 × Ba(2+) in a distorted, mono-capped square prism) for the [BN2](3-) units with B-N distances of 132 and 136 pm. Vibrational spectra of SrBa8[BN2]6 and EuBa8[BN2]6 confirm the discrete linear [BN2](3-) units and (11)B solid state MAS NMR spectra are compatible with single crystallographic sites for the boron atoms. In EuBa8[BN2]6 the spectra are profoundly influenced by interactions of the (11)B nuclei with the unpaired electrons of the paramagnetic Eu(2+) ions.

Photoluminescence and afterglow of deep red emitting SrSc2O4:Eu2+

This work deals with the photoluminescence as well as the persistent luminescence of SrSc₂O₄:Eu²⁺ and SrSc₂O₄:Eu²⁺,Dy³⁺. Therefore, photoluminescence spectra were recorded and fluorescence lifetime measurements were performed.

Photochemical synthesis of CeO2 nanoscale particles using sodium azide as a photoactive material: effects of the annealing temperature and polyvinylpyrrolidone addition

The size of CeO₂ nanoparticles can be controlled by VUV irradiation time and post annealing temperature.

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

The cluster (TBA)₂[W₆I₈(CF₃COO)₆] shows photoluminescence in the solid state and in solution, and singlet oxygen (a¹Δ_g) is generated in the presence of oxygen.

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.

New Red-Emitting Phosphor La2Zr3(MoO4)9:Eu3+ and the Influence of Host Absorption on its Luminescence Efficiency

This work investigates the optical properties of Eu3+-activated La2Zr3(MoO4)9. A series of solid solutions with Eu3+ concentrations in the range of 0–100 % were prepared by conventional high temperature solid-state synthesis. An unusual change in the lattice parameters was observed. The phosphor exhibits a broad absorption band in the UV spectral region, and measurements on the non-doped material at 100 K were conducted to elucidate the nature of the absorption band. As demonstrated, Mo6+ charge transfer absorption negatively influences the luminescence efficiency of the phosphor. The temperature-dependent emission spectra revealed that the emission intensity exhibits a bi-sigmoidal temperature dependence. This behaviour results from competing absorption via Mo6+ charge transfer processes, which strongly decrease the efficiency of the phosphor. For application purposes, it is therefore advisable to choose materials that do not exhibit host absorption in the spectral range where excitation is expected.