Physicochemical, structural and fluorescence properties of Er-doped Ge-S-Ga glasses

Erbium-doped (GeS₂)_x(Ga₂S₃)_100−x (x=75, 80, 85, 90 mol%) glasses have been characterized by some basic parameters, which are important from a practical point of view. The influence of Er by introduction of 0.3, 0.6, and 0.9 mol% Er₂S₃ on the properties has been studied. The glasses have relatively high glass transition temperatures and high thermal stability, the maximal being at x=80 (the difference between the crystallization and glass transition temperatures has been found to be 150 °C. The values of Vickers microhardness and density increase with increasing GeS₂ content, slightly depending on the presence of the Er³⁺ ions. The distribution and changes of the structural units, caused by addition of Ga₂S₃ and Er₂S₃ to GeS₂, have been specified by the Raman scattering in the range 50-550 cm⁻¹. The intensity dependence of the luminescence on glass composition has been evaluated. The glasses have shown a good chemical durability and their resistance to the moisture is relatively high. The obtained results have supported possible applications of these glasses in rare-earth doped devices.     

The 2ν4 overtone bands of FClO3

The high resolution infrared spectrum of the mono-isotopic species F³⁵Cl¹⁶O₃ has been studied in the region of the 2ν₄ overtone, from 2560 to 2680 cm⁻¹. The perpendicular component is strong and clearly observed while the parallel component is very weak and almost completely hidden by the perpendicular one. Their origins differ by 12.6 cm⁻¹, the being located at higher wavenumbers. The band is perturbed by the anharmonic interaction between the v₄ = 2, l₄ = ?2 and v₂ = v₄ = v₅ = 1, l₄ = l₅ = ±1 excited states, both of E symmetry. In total 3157 transitions have been assigned, 83% of these to , 12% to , and 5% to . The three bands have been analyzed simultaneously, taking into account the Fermi resonance effective between the excited states of E symmetry. The ro-vibration parameters of the excited states have been obtained, including the deperturbed band origins of and , at 2628.5890(4) and 2619.3342(5) cm⁻¹, respectively. The W₂₄₅ anharmonic constant is equal to 4.0161(4) cm⁻¹. The x₄₄+g₄₄ and x₂₄+x₄₅+g₄₅ anharmonicity constants have been derived from the obtained band origins and those of ν₄ and ν₂ + ν₅.     

The 2ν5 overtone bands of perchloryl fluoride

The high-resolution infrared spectra of the monoisotopic species F³⁵Cl¹⁶O₃, F³⁷Cl¹⁶O₃, F³⁵Cl¹⁸O₃ and F³⁷Cl¹⁸O₃ have been studied in the region of the 2ν₅ overtones, from 1100 to 1200 cm⁻¹. Both the parallel and the perpendicular components are clearly observed in the spectra, their origins differing by about 0.4 cm⁻¹. In each spectrum about 2000 transitions have been assigned, 35% of them belonging to . The parallel and perpendicular bands in each manifold have been analyzed separately since no evidence of perturbations has been observed. The rovibration parameters of the v₅ = 2, l₅ = 0 and v₅ = 2, l₅=?2 excited states have been obtained. For the four species combining the and band origins with those of the ν₅ fundamentals the harmonic wavenumbers, , and the x₅₅ and g₅₅ anharmonicity constants have also been derived.     

Surface defect states of CdTexS1 − x quantum dots

Properties of surface defect states of CdTe_xS_1 − x quantum dots with an average diameter of 7 nm are investigated experimentally. The stoichiometric ratio is found to be for by use of the energy dispersive analysis of x-ray. The photoluminescence spectrum, the photoluminescence excitation spectrum, and the surface passivation are adopted to characterize the properties of surface defect states. The energy levels of surface defect states of CdTe_xS_1 − x quantum dots are also determined.     

Time-resolved infrared diode laser spectroscopy of the ν1 (C-O stretch) band of the CoCO radical

Infrared spectrum of the cobalt carbonyl radical CoCO produced by the 193 nm excimer laser photolysis of cobalt tricarbonyl nitrosyl Co(CO)₃NO was observed by time-resolved diode laser spectroscopy. More than 600 lines were identified as belonging to the ν₁ (C-O stretch) fundamental band, consisting of the Ω=5/2 and 3/2 subbands, and the associated hot bands , , , and . The ²Δ_i electronic ground state of CoCO was experimentally confirmed. The ν₁ band origins are 1974.172582(93) cm⁻¹ and 1973.53178(14) cm⁻¹ for the Ω=5/2 and 3/2 subbands, respectively. The rotational constant in the ground state was determined as B₀=4427.146(50) MHz. The centrifugal distortion constant D₀=1.1243(68) kHz was obtained for the Ω=5/2 substate of the ground state. The equilibrium rotational constant B_e=4435.44(14) MHz was derived, together with the vibration-rotation interaction constants.     

Spin-Peierls and incommensurate states in layered S=1/2 system TiOCl

We demonstrate that TiOCl is a good model inorganic system to investigate spin-Peierls state. Our ³⁵Cl and ^47,49Ti NMR data show that a pseudo spin-gap behavior below T*=135 K precedes successive phase transitions at T_c=94 K and into a singlet spin-Peierls ground state with a large energy gap E_g/k_B=430 K.     

Optical characterization of Mn, Ni and Co ions doped zinc lead borate glasses

This paper reports on the development and optical characterization of heavy metal oxide (HMO)-based transparent glasses in the chemical composition of 15PbO-40B₂O₃-(45−x) ZnO−x TM²⁺ (=Mn²⁺ or Ni²⁺ or Co²⁺) (where x=0.2, 0.5 mol%). For these glasses both absorption and emission spectra have been measured, in order to understand their optical performances. The XRD profiles have confirmed their glassy nature and the FTIR spectral features have been analyzed. From the emission spectra, a bright green emission (538 nm) from Mn²⁺-glasses, an intense red emission (670 nm) from Ni²⁺ and from Co²⁺ (625 nm) glasses have been noticed very clearly. Based on the UV-absorption spectra of these materials, both direct and indirect bond gaps have been computed. Apart from the spectral analysis, different physical properties of these glasses have also been carried out. Due to the presence of both PbO and ZnO, these glasses are found to be good moisture-resistant optical systems. Both optical and physical properties have been found to be more encouraging towards their use as novel luminescent optical materials.     

Exhibition of low hyperfine coupling constant for copper(II) in magnesium rubidium sulphate hexahydrate

Single crystal EPR studies of Cu(II) incorporated in magnesium rubidium sulphate hexahydrate are carried out at RT and 77 K. Since the hyperfine lines are not resolved at RT, single crystal rotations have been carried out at 77 K. The spin Hamiltonian parameters calculated from the 77 K spectra are: g₁₁=2.133, g₂₂=2.137, g₃₃=2.327, A₁₁=0.01, A₂₂=1.44 and . The impurity ion occupies an interstitial position in this crystal lattice, which is not very common for copper ion. In addition, the low hyperfine coupling constant is explained by considering an admixture of dx²-y² ground state with dz² excited state. Bonding parameters, κ=0.254, , α²=0.706, α=0.8406 have also been calculated. The present study has helped to understand the static nature of JT, for which the present system is an example.     

Nanophases in mechanochemically synthesized AgI-CuI system: structure, phase stability and phase transitions

Nanoscale crystallites of Ag-rich (Ag_1−xCu_xI, x=0.05, 0.10, 0.15 and 0.25), Cu-rich (Cu_1-yAg_yI, y=0.05, 0.10, 0.15 and 0.25) and intermediate Ag_1-xCu_xI (x=0.50) solid solutions and end members AgI, CuI with sizes in the range of 46-13 nm were synthesized by attrition at ambient temperature in a soft mechanochemical reaction (MCR) of Ag, Cu and I. Monophasic γ-AgI (zincblende, ) with disordered Ag⁺ sublattice and the crystallite size of about ∼31 nm was realized in the case of Ag_0.75Cu_0.25I (x=0.25) composition. Lattice parameter decreases linearly from 649 to 604 pm with increasing Cu concentration in the AgI-CuI system validating Vegard's law. Smallest size (∼13 nm) agglomerated nanocrystals were realized in the Cu-rich composition Cu_0.75Ag_0.25I (), while unagglomerated uniform-sized (∼17 nm) and spherical shape nanocrystallites of Ag_0.50Cu_0.50I () with maximum strain were synthesized for sensor applications using MCR. Differential scanning calorimetry study shows the systematic changes in the phase transition temperature with Cu substitution. Ag-rich composition posses less enthalpy (ΔH (x or Cu=0.05, 0.10, 0.15, 0.25)=6.0, 6.11, 6.6, 6.3 in kJ/mol) and entropy (ΔS (y or Ag=0.05, 0.10, 0.15, 0.25)=14.15, 14.1, 15.03, 13.6 in J/mol K) when compared to undoped AgI () implying greater thermal stability of γ-phase due to Cu-strengthened Ag-I bond. Enhanced entropy () in Cu_0.75Ag_0.25I (Cu-rich) solid solutions relative to CuI () indicates Ag-induced cation disorder. Fifteen percent Ag-doped CuI (Cu_0.85Ag_0.15I) nanocrystals apparently behave like microscopic p-n junctions with currents in the range of 10⁻⁶-10⁻⁸ A characterized by a non-linear I-V curve.     

Stretch-bend combination polyads in the ÃAu state of acetylene, C2H2

Rotational analyses are reported for a number of newly-discovered vibrational levels of the S₁-trans (ùA_u) state of C₂H₂. These levels are combinations where the Franck-Condon active and vibrational modes are excited together with the low-lying bending vibrations, and . The structures of the bands are complicated by strong a- and b-axis Coriolis coupling, as well as Darling-Dennison resonance for those bands that involve overtones of the bending vibrations. The most interesting result is the strong anharmonicity in the combinations of (trans bend, a_g) and (in-plane cis bend, b_u). This anharmonicity presumably represents the approach of the molecule to the trans-cis isomerization barrier, where ab initio results have predicted the transition state to be half-linear, corresponding to simultaneous excitation of and . The anharmonicity also causes difficulty in the least squares fitting of some of the polyads, because the simple model of Coriolis coupling and Darling-Dennison resonance starts to break down. The effective Darling-Dennison parameter, K₄₄₆₆, is found to increase rapidly with excitation of , while many small centrifugal distortion terms have had to be included in the least squares fits in order to reproduce the rotational structure correctly. Fermi resonances become important where the K-structures of different polyads overlap, as happens with the 2¹3¹B¹ and 3¹B³ polyads (B = 4 or 6). The aim of this work is to establish the detailed vibrational level structure of the S₁-trans state in order to search for possible S₁-cis (¹A₂) levels. This work, along with results from other workers, identifies at least one K sub-level of every single vibrational level expected up to a vibrational energy of 3500 cm⁻¹.     

Investigation of spectroscopic properties and thermal stability of Er/Yb-co-doped Bi2O3-B2O3-Ga2O3 glasses

A series of Er³⁺/Yb³⁺-co-doped 60Bi₂O₃-(40−x) B₂O₃ -xGa₂O₃ (BBGA x=0, 4, 8, 12, 16 mol%) glasses have been prepared. The absorption spectra, emission spectra, fluorescence lifetime of Er³⁺:⁴I_13/2 level and thermal stability were measured and investigated. Three Judd-Ofelt intensity parameters Ω_t (t=2,4,6) (Ω₂=(4.67-5.93)×10⁻²⁰ cm², Ω₄=(1.50-1.81)×10⁻²⁰ cm², Ω₆=(0.92-1.17)×10⁻²⁰ cm²) of Er³⁺ ions were calculated by Judd-Ofelt theory. It is found that the Ω₆ first increases with the increase of Ga₂O₃ content from 0 to 8 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section () of Er³⁺: ⁴I_13/2→⁴I_15/2 transition were obtained according to McCumber theory and broad full width at half maximum (FWHM=69-76 nm) of the ⁴I_13/2→⁴I_15/2 transition of Er³⁺ ions were measured. The results indicate that these new BBGA glasses can be used as a candidate host material for potential broadband optical amplifiers.     

Spectroscopic characterization of the potential energy functions of Ne2 Rydberg states in the vicinity of the Ne(S0) + Ne(4p′) dissociation limits

The gerade autoionizing Rydberg states of Ne₂ have been studied in the range 162 000-172 000 cm⁻¹ by 1 + 1′ resonant two-photon excitation from the Ne₂ X ground state via different vibrational levels of the Ne₂ C state. A rotationally resolved part of the spectrum allowed the determination of the potential energy functions of two states of 1_g and characters in the vicinity of the Ne(2p⁶¹S₀) + Ne (2p⁵4p′) dissociation limit. The presence of maxima in these potential energy functions is interpreted as originating from a repulsive interaction between the Rydberg electron and the neutral atom.     

Rotational and vibrational structure in the 288 nm band system of the FeCl2 radical

The laser excitation spectrum of the 288 nm band system of FeCl₂, formed in a free-jet expansion, has been recorded at a rotational temperature of approximately 10 K. Vibronic transitions are observed from the ground state to two close-lying excited electronic states that differ in inversion (g, u) parity. Two extensive progressions in the symmetric stretching vibration have been identified, referred to as Progressions A and B. The main features of Progression A, which is based on the band, are allowed transitions to the excited electronic state of ungerade symmetry. Progression B is built on the band and consists of vibronically induced transitions to the gerade excited state. A substantial decrease in the symmetric stretching vibrational wavenumber is observed on excitation . Local perturbations are found to cause relative shifts between the different isotopomers. Several vibronic bands have been recorded and analysed at rotational resolution for the three isotopomers Fe³⁵Cl₂, Fe³⁵Cl³⁷Cl, and Fe³⁷Cl₂ in natural abundance. All bands show perpendicular rotational structure of a linear molecule, and have been unambiguously assigned to a Ω = 5-4 transition, consistent with the inverted ⁵Δ_g ground state predicted by ab initio and DFT calculations. The zero-point averaged FeCl bond length is determined to be in the upper and lower electronic states. The results show that the molecule is linear in both states.     

A theoretical study of BrCN in the Π electronic ground state: Large amplitude bending motion

We have calculated the three-dimensional potential energy surfaces for the 1 ²A′ and 1 ²A″ states of BrCN⁺ at the MR-SDCI_DK+Q/[QZP-ANO-RCC (Br, C, N)] level of theory, where MR-SDCI_DK means ‘multi-reference single and double excitation configuration interaction calculation with Douglas-Kroll Hamiltonian.’ These ab initio potential energy surfaces have a common minimum (corresponding to the state) at a linear equilibrium structure with r_e(Br-C) = 1.735 Å and r_e(C-N) = 1.199 Å. Variational RENNER calculations yield a zero-point averaged structure (with the structural parameters calculated as expectation values over rovibrational wavefunctions) with 〈r(Br-C)〉₀ = 1.739 Å, 〈r(C-N)〉₀ = 1.204 Å, and 〈∠(Br-C-N)〉₀ = 172(4)°. A severe Fermi resonance between 2ν₂ and ν₃ has been found theoretically for the ²A″ potential energy surface. Comparing the ab initio zero-point averaged structure with a recent, experimentally derived r₀ structure, it is concluded that the effects of large-amplitude bending motion should be taken into account explicitly in the process of deriving the r₀ structure from the experimental values of the rotational constants. The electronic structure of BrCN⁺ has also been discussed.