Mid-IR nonlinear optical (NLO) materials are of great importance in modern laser frequency conversion technology and optical parametric oscillator processes. However, the commercially available IR NLO crystals (e.g., AgGaQ2 (Q = S, Se) and ZnGeP2) suffer from two obstacles, low laser damage thresholds (LDTs) and the difficulty of obtaining high-quality crystals, both of which seriously hinder their applications. The introduction of Cl, an element with a large electronegativity, and Pb, a relatively heavy element to promote the optical properties, affords an oxide-based IR NLO material, Pb17O8Cl18 (POC). High-quality POC single crystals with sizes of up to 7 mm × 2 mm × 2 mm have been grown in an open system. Additionally, POC exhibits a large LDT of 408 MW/cm(2), 12.8 times that of AgGaS2. POC also exhibits an excellent second harmonic generation response: 2 times that of AgGaS2, the benchmark IR NLO crystal at 2090 nm, and 4 times that of KDP, the standard UV NLO crystal at 1064 nm. Thus, we believe that POC is a promising IR NLO material.

Birefringent materials are of great importance in optical communication and the laser industry, as they can modulate the polarization of light. Limited by their transparency range, few birefringent materials, except α-BaB2O4 (α-BBO), can be practically used in the deep ultraviolet (UV) region. However, α-BBO suffers from a phase transition and does not have enough transparency in the deep UV region. By introducing the relatively small alkali metal Na+ cation and the F– anion to keep the favorable structural features of α-BBO, we report a new birefringent crystal Na3Ba2(B3O6)2F (NBBF), which has the desirable optical properties. NBBF not only maintains the large birefringence (Δn = n o – n e = 0.2554–0.0750 from 175 nm to 3.35 μm) and extends its UV cutoff edge to 175 nm (14 nm shorter than α-BBO) but also eliminates the phase transition and has the lowest growth temperature (820 °C) among birefringent materials. These results demonstrate that NBBF is an attractive candidate for the next generation of deep UV birefringent materials.

We have experimentally observed self-trapped holes (STHs) in a β-Ga2O3 crystal using electron paramagnetic resonance (EPR). These STHs are an intrinsic defect in this wide-band-gap semiconductor and may serve as a significant deterrent to producing usable p-type material. In our study, an as-grown undoped n-type β-Ga2O3 crystal was initially irradiated near room temperature with high-energy neutrons. This produced gallium vacancies (acceptors) and lowered the Fermi level. The STHs (i.e., small polarons) were then formed during a subsequent irradiation at 77 K with x rays. Warming the crystal above 90 K destroyed the STHs. This low thermal stability is a strong indicator that the STH is the correct assignment for these new defects. The S = 1/2 EPR spectrum from the STHs is easily observed near 30 K. A holelike angular dependence of the g matrix (the principal values are 2.0026, 2.0072, and 2.0461) suggests that the defect's unpaired spin is localized on one oxygen ion in a nonbonding p orbital aligned near the a direction in the crystal. The EPR spectrum also has resolved hyperfine structure due to equal and nearly isotropic interactions with 69,71Ga nuclei at two neighboring Ga sites. With the magnetic field along the a direction, the hyperfine parameters are 0.92 mT for the 69Ga nuclei and 1.16 mT for the 71Ga nuclei.

Atomic-scale defects on the surface of Cu2O(111) are characterized through UHV STM measurements, DFT calculations and STM simulations.

Single crystals of cuprous oxide (Cu2O) with minimal defects were grown using the optical floating zone technique. Copper vacancies were removed through the promotion of CuO precipitation within the bulk Cu2O crystal following the reaction CuCu Cu2O + VCu Cu2O + OO Cu2O → CuCu CuO + OO CuO. This reaction was promoted through the use of high purity samples and by growing crystals under an oxidizing atmosphere. Although an increase in the oxygen concentration of the atmosphere will initially increase the oxygen to copper ratio, the excess oxygen in the final Cu2O crystal is ultimately decreased through the formation of CuO as the crystal cools. Copper vacancies were reduced further, and the CuO phase was eventually removed from the Cu2O crystal when thin slices of the crystal were annealed.

b S Supporting Information ' INTRODUCTIONTemplated metal oxides have attracted sustained interest for many years, owing to their remarkably high degrees of compositional and structural diversity 1 and for technologically desirable physical properties. 2 However, increasing demand for new materials with enhanced properties has highlighted the lack of design and predictability in the syntheses of such compounds. The greatest limitation lies in our poor understanding of the mechanisms by which these compounds form. 3 While mechanisms have been postulated, 4À8 true design remains elusive. Significant progress has been made in the identification of reaction parameters that most strongly influence the formation of these materials.The primary influence over the structure of the inorganic component is reagent composition. Differences in reactant concentrations are known to directly affect the identity and availability of the primary building units from which the inorganic components are constructed. 9À14 Reactant concentrations are clearly affected by a range of experimental parameters, ranging from the dependence of metal speciation on both pH and temperature to differences associated with source materials and reaction times. The manner in which the inorganic reactants oligomerize and polymerize in the systems described above is thought to be controlled by charge density matching 4,5 between the organic cations and the anionic inorganic synthons. This secondary influence allows for crystallization only after the charge densities of the cationic and anionic components match. The importance of charge density matching has been demonstrated in a range of systems, including silicates, 15À17 oxovanadium phosphates, 18 gallium phosphates, 4,5 molybdates, 19 and vanadium tellurites. 20 Despite the utility of the charge density matching approach, differences in reactant concentrations and amine pK a alone do not wholly dictate the connectivities and structures of the resulting inorganic architectures. Charge density matching cannot differentiate between markedly different inorganic structures that have nearly identical charge densities. For example, we have reported the formation of both [Mo 3 O 10 ] n 2nÀ and [Mo 8 O 26 ] n 4nÀ chains from reactions in which the respective amines had similar pK a 's and were used in nearly identical concentrations. 19 We have also observed both [V 2 Te 2 O 10 ] n 2nÀ chains and [V 2 TeO 8 ] n 2nÀ layers in reactions containing either 1,4-diaminobutane or 1,3-diaminopropane, respectively. 20 In each system, the differences in charge densities of the inorganic components are small. As such, a series of tertiary influences has been proposed, including amine symmetry and hydrogen-bonding preferences. 19À21 This report contains an elucidation and observation of tertiary influences in the formation of new organically templated vanadium tellurites. The NaVO 3 /Na 2 TeO 3 /2,5-dimethylpiperazine and NaVO 3 /Na 2 TeO 3 /2-methylpiperazine systems were explored using composition space analysis, result...

The role of charge density matching was investigated in the formation of templated vanadium tellurites under mild hydrothermal conditions. Reactions were conducted using a fixed NaVTeO(5):amine ratio in an ethanol/water solution to isolate the effects of amine structure. The use of 1,4-diaminobutane, 1,3-diaminopropane, and piperazine resulted in three distinct vanadium tellurite connectivities, [V(2)Te(2)O(10)](n)(2n-) chains, [V(2)TeO(8)](n)(2n-) layers, and [V(2)Te(2)O(10)](n)(2n-) layers, respectively. Charge density matching with the protonated amines is the primary influence over the structure of each vanadium tellurite anion, as quantified by molecular surface area and geometric decomposition methods. Electron localization functions were calculated using the Stuttgart tight-binding linear muffin-tin orbital, atomic sphere approximation code, to visualize the location and relative size, shape, and orientation of the stereoactive lone pair in the tellurite groups. [C(4)H(14)N(2)][V(2)Te(2)O(10)]: a = 5.649(5) A, b = 6.348(5) A, c = 9.661(5) A, alpha = 84.860(5) degrees , beta = 85.380(5) degrees , gamma = 81.285(5) degrees , triclinic, P1 (No. 2), Z = 1.

Phonons are produced when an excited vacancy in cuprous oxide (Cu 2 O) relaxes. Time resolved luminescence was used to find the excited copper vacancy (acceptor) and oxygen vacancy (donor) trap levels and lifetimes. It was also used to determine the typical energy and number of phonons in the phonon pulses emitted by vacancies. The vacancy properties of cuprous oxide are controlled by several synthesis parameters and by the temperature. We directly demonstrate the absorption of light by oxygen vacancies with transient absorption. Copper and oxygen vacancies behave differently, in part because the two kinds of traps capture carriers from different states. For example, the copper vacancy luminescence lifetime is around 25 times greater at low temperature. However, both kinds of vacancy luminescence are consistent with a Poissonian multiple phonon emission model.