Luminescence of nanocrystalline BaFCl codoped with Eu and Tb.

BaFCl:Eu,Tb nanocrystals were synthesized hot-injection thermolysis of metal chlorodifluoroacetates and their luminescence response characterized between 80 and 430 K. Though unintended, partial reduction of Eu to Eu occurred during the synthesis stage, leading to luminescent nanocrystals coactivated by Eu, Eu, and Tb. Their emission was dominated by Eu, specifically by radiative transitions 4f (P) → 4f (S) and 4f5d (lowest level) → 4f (S).

Exploiting the Reactivity of Metal Trifluoroacetates to Access Alkali-Niobium(V) Oxyfluorides.

Motivated by the lack of facile routes to alkali-niobium(V) oxyfluorides KNbOF and CsNbOF, we investigated the reactivity of alkali trifluoroacetates KH(tfa) and CsH(tfa) (tfa = CFCOO) toward NbO in the solid state. Tetragonal tungsten bronze KNbOF and pyrochlore CsNbOF were obtained by simply reacting the corresponding trifluoroacetate with NbO at 600 °C under air, without the need for specialized containers or a controlled atmosphere. Thermolysis of KH(tfa) in the presence of NbO yielded single-phase polycrystalline KNbOF.

Reactivity of bi- and monometallic trifluoroacetates towards amorphous SiO.

The reactivity of alkali-manganese(II) and alkali trifluoroacetates towards amorphous SiO (a-SiO) was studied in the solid-state. KMn(tfa), CsMn(tfa)(tfaH), KH(tfa), and CsH(tfa) (tfa = CFCOO) were thermally decomposed under vacuum in fused quartz tubes. Three new bimetallic fluorotrifluoroacetates of formulas KMn(tfa)F, CsMn(tfa)F, and KMn(tfa)F were discovered upon thermolysis at 175 °C.

Synthesis, Structure, and Luminescence of Mixed-Ligand Lanthanide Trifluoroacetates.

A series of new mixed-ligand lanthanide trifluoroacetates of formula Ln(4-cpno)(tfa)(HO)·HO (Ln = Sm, Eu, Gd, Tb, Dy; 4-cpno = 4-cyanopyridine -oxide; tfa = trifluoroacetate) is reported. Trifluoroacetates were synthesized as chemically pure polycrystalline solids and their crystal structures were probed using single-crystal and powder X-ray diffraction. Ln(4-cpno)(tfa)(HO)·HO solids make up an isostructural series in which LnO polyhedra are bridged by 4-cpno to form edge-sharing dimers.

Structure-Dependent Accessibility of Phonon-Coupled Radiative Relaxation Pathways Probed by X-ray-Excited Optical Luminescence.

Rare-earth scheelites represent a diverse family of compounds with multiple degrees of freedom, which enables the incorporation of a wide range of lanthanide color centers. Precise positioning of quantum objects is attainable by the choice of alkali cations and lattice connectivity of polyanion units. Herein, we report the structure-dependent energy transfer and lattice coupling of optical transitions in La- and Dy-containing scheelite-type double and quadruple molybdates NaLaDy(MoO) and NaLaDy(MoO).

Expanding the synthetic toolbox to access pristine and rare-earth-doped BaFBr nanocrystals.

A new synthetic route to access pristine and rare-earth-doped BaFBr nanocrystals is described. Central to this route is an organic-inorganic hybrid precursor of formula Ba(CFBrCOO)(HO) that serves as a dual-halogen source. Thermolysis of this precursor in a mixture of high-boiling point organic solvents yields spherical BaFBr nanocrystals (≈20 nm in diameter).

Ratiometric Thermometry Using Thermochromic Tb:Mn:NaMg(WO) Phosphors.

The utility of Tb:Mn:NaMg(WO) phosphors as ratiometric luminescent thermometers in the 200-450 K temperature range is demonstrated. Targeted substitution of Tb for Na and Mn for Mg yields phosphors of formula NaTbMgMn(WO). UV excitation of the NaMg(WO) host results in green emission from terbium (544 nm) and red emission from manganese (682 nm).

Bimetallic Trifluoroacetates as Precursors to Layered Perovskites AMnF (A = K, Rb, and Cs).

Four novel alkali-manganese(II) trifluoroacetates were synthesized, and their potential as self-fluorinating precursors to layered perovskites AMnF (A = K, Rb, and Cs) was demonstrated. NaMn(tfa), KMn(tfa), RbMn(tfa)·0.23HO, and CsMn(tfa)(tfaH) (tfa = CFCOO and tfaH = CFCOOH) were grown as single crystals, and their crystal structures solved using X-ray diffraction.

Microwave-assisted solid-state synthesis of NaRE(MO) phosphors (RE = La, Pr, Eu, Dy; M = Mo, W).

A synthetic method was developed to enable the microwave-assisted solid-state preparation of double molybdate and double tungstate scheelite-type phosphors of formula NaRE(MO4)2 (RE = La, Pr, Eu, Dy; M = Mo, W). Starting from subgram-scale stoichiometric mixtures of metal carbonates and oxides and with the aid of granular activated charcoal as a microwave susceptor, ternary (NaEu(MO4)2), quaternary (NaLa0.95Eu0.

Room-Temperature Broadband Light Emission from Hybrid Lead Iodide Perovskite-Like Quantum Wells: Terahertz Spectroscopic Investigation of Metastable Defects.

The properties of mid-band-gap electronic states are central to the potential application of self-assembled, hybrid organic-inorganic perovskite-like quantum wells in optoelectronic technologies. We investigate broadband light emission from mid-band-gap states in fast-forming hybrid organic lead iodide quantum wells at room temperature. By comparing temperature- and intensity-dependent photoluminescence (PL) spectra emitted from butyl ammonium spaced inorganic layers, we propose that structural defects in a metastable material phase trap excitons and cause broadband light emission spanning wavelengths between 600 and 1000 nm.

Rubidium-Alkaline-Earth Trifluoroacetate Hybrids as Self-Fluorinating Single-Source Precursors to Mixed-Metal Fluorides.

Three novel bimetallic hybrid crystals featuring rubidium-alkaline-earth metal pairs and trifluoroacetato ligands were synthesized, and their utility as self-fluorinating single-source precursors to the corresponding mixed-metal fluorides was demonstrated. RbMg(tfa)(tfaH)·3HO, RbCa(tfa), and RbSr(tfa) (tfa = CFCOO; tfaH = CFCOOH) were synthesized in both single-crystal and polycrystalline forms via solvent evaporation. Their crystal structures were solved using single-crystal X-ray diffraction (XRD), and chemical purity was confirmed using thermal analysis (TGA/DTA).

n-Type PbSe Quantum Dots via Post-Synthetic Indium Doping.

We developed a postsynthetic treatment to produce impurity n-type doped PbSe QDs with In as the substitutional dopant. Increasing the incorporated In content is accompanied by a gradual bleaching of the interband first-exciton transition and concurrently the appearance of a size-dependent, intraband absorption, suggesting the controlled introduction of delocalized electrons into the QD band edge states under equilibrium conditions. We compare the optical properties of our In-doped PbSe QDs to cobaltocene treated QDs, where the n-type dopant arises from remote reduction of the PbSe QDs and observe similar behavior.

Photophysical characterization of a highly luminescent divalent-europium-containing azacryptate.

We report a new luminescent EuII-containing complex. The complex is excited with visible light, leading to emission centered at 447 nm with a lifetime of 1.25 μs.

Bimetallic Trifluoroacetates as Single-Source Precursors for Alkali-Manganese Fluoroperovskites.

Alkali-manganese(II) trifluoroacetates were synthesized, and their potential as single-source precursors for the solid-state and solution-phase synthesis of AMnF fluoroperovskites (A = Na, K, Rb, Cs) was demonstrated. Crystals of NaMn(tfa)(tfaH), KMn(tfa)(tfaH)·HO, RbMn(tfa)·HO, and CsMn(tfa) (tfa = trifluoroacetato) were grown via solvent evaporation and their crystal structures solved using single-crystal X-ray diffraction (XRD). Chemical purity was confirmed using thermal analyses (TGA/DTA) and Rietveld analysis of powder XRD patterns.

Synthesis of bimetallic trifluoroacetates through a crystallochemical investigation of their monometallic counterparts: the case of (A, A')(CFCOO)·nHO (A, A' = Mg, Ca, Sr, Ba, Mn).

Owing to their potential as single-source precursors for compositionally complex materials, there is growing interest in the rational design of multimetallic compounds containing fluorinated ligands. In this work, we show that chemical and structural principles for a materials-by-design approach to bimetallic trifluoroacetates can be established through a systematic investigation of the crystal-chemistry of their monometallic counterparts. A(CFCOO)·nHO (A = Mg, Ca, Sr, Ba, Mn) monometallic trifluoroacetates were employed to demonstrate the feasibility of this approach.

Open-Framework Structures of Anhydrous Sr(CF3COO)2 and Ba(CF3COO)2.

Anhydrous Sr(CF3COO)2 and Ba(CF3COO)2 open-framework structures featuring three-dimensional connectivity of metal-oxygen polyhedra were crystallized from a mixture of water and CF3COOH. Crystallization was induced via evaporation of the solvent mixture under a dry nitrogen flow. This approach differs from that routinely employed for crystallization of metal trifluoroacetates, which achieves solvent evaporation by heating under air and yields hydrated salts.

Complex perovskite oxide nanocrystals: low-temperature synthesis and crystal structure.

This Perspective reviews our recent efforts towards the low-temperature synthesis of complex perovskite oxide ABO3 (A = Sr, Ba; B = Ti, Zr) nanocrystals using the vapor diffusion sol-gel method and the determination of their room-temperature crystal structure. From a synthetic standpoint, emphasis is placed on demonstrating the ability of the vapor diffusion sol-gel approach to yield compositionally complex nanocrystals at low temperatures and atmospheric pressure without the need for postsynthetic heat treatment to achieve a crystalline and phase-pure oxide product. The ability to successfully achieve this is illustrated using Ba1-xSrxTi1-yZryO3 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1) and Eu(3+)-doped Ba(Ti,Zr)O3 nanocrystals as examples.

Local structural investigation of Eu(3+)-doped BaTiO3 nanocrystals.

A structural investigation of sub-15 nm xEu:BaTiO3 nanocrystals (x = 0-5 mol%) was conducted to determine the distribution of the Eu(3+) ion in the BaTiO3 lattice. Pair distribution function analysis of X-ray total scattering data (PDF), steady-state photoluminescence, and X-ray absorption spectroscopy (XANES/EXAFS) were employed to interrogate the crystal structure of the nanocrystals and the local atomic environment of the Eu(3+) ion. The solubility limit of the Eu(3+) ion in the nanocrystalline BaTiO3 host synthesized via the vapor diffusion sol-gel method was estimated to be ∼4 mol%.

Local structure of Ba(1-x)Sr(x)TiO3 and BaTi(1-y)Zr(y)O3 nanocrystals probed by X-ray absorption and X-ray total scattering.

The effect of isovalent chemical substitution on the magnitude and coherence length of local ferroelectric distortions present in sub-20 nm Ba(1-x)Sr(x)TiO3 (x = 0.0, 0.30, 0.

Structural disorder in AMoO4 (A = Ca, Sr, Ba) scheelite nanocrystals.

The crystal structure of sub-15 nm AMoO4 (A = Ca, Sr, Ba) scheelite nanocrystals has been investigated using a dual-space approach that combines Rietveld and pair distribution function (PDF) analysis of synchrotron X-ray diffraction data. Rietveld analysis yields an average crystal structure in which the Mo-O bond distance exhibits an anomalously large contraction (2.8%) upon chemical substitution of Ba(2+) for Ca(2+).

Structural evolution of BaTiO(3) nanocrystals synthesized at room temperature.

Sub-10 nm BaTiO(3) nanocrystals were synthesized at room temperature via the vapor diffusion sol-gel method, and their structural evolution during nucleation and growth stages was followed using a series of techniques that probe the atomic structure on different length and time scales. Special emphasis was placed on assessing the evolution of the local symmetry and structural coherence of the resulting nanocrystals, as these are the structural bases for cooperative properties such as ferroelectricity. Although the room-temperature crystal structure of the fully grown nanocrystals appears cubic to Rietveld analysis of synchrotron X-ray diffraction data, Raman spectroscopy and pair distribution function analysis demonstrate the presence of non-centrosymmetric regions arising from the off-centering of the titanium atoms.

Vapor diffusion sol-gel synthesis of fluorescent perovskite oxide nanocrystals.

A model system consisting of Eu(3+) as the activator ion and BaZrO(3) as the host lattice is employed to demonstrate the potential of the vapor diffusion sol-gel method as a hydrolytic approach to the synthesis of fluorescent alkaline-earth perovskite oxide nanocrystals under ultrabenign conditions. The resulting nanocrystals are suitable precursors for nanostructured red-emitting phosphors.

Local structural distortion of BaZr(x)Ti(1-x)O3 nanocrystals synthesized at room temperature.

Single crystalline, sub-15 nm BaZr(x)Ti(1-x)O(3) (0 ≤x≤ 1) nanocrystals were synthesized at room temperature via the vapor diffusion sol-gel method. As-prepared nanocrystals exhibit noncentrosymmetric regions whose volume fraction increases significantly upon substitution of small amounts of Zr(4+) for Ti(4+) and reaches a maximum for substitution levels ranging from 10 to 20 mol%.

Controlled growth of platinum nanoparticles on strontium titanate nanocubes by atomic layer deposition.

With an eye toward using surface morphology to enhance heterogeneous catalysis, Pt nanoparticles are grown by atomic layer deposition (ALD) on the surfaces of SrTiO(3) nanocubes. The size, dispersion, and chemical state of the Pt nanoparticles are controlled by the number of ALD growth cycles. The SrTiO(3) nanocubes average 60 nm on a side with {001} faces.