Migration and Annihilation of Triplet Excitation Energy in the Charge-Transfer Anthracene-Tetrachlorophtalic Anhydride Crystal

Abstract

The emission spectra of the charge-transfer crystal of anthracene-tetrachlorophtalic anhydride were studied in the 1.7-300 K temperature range. Delayed fluorescence was observed over the whole temperature range. At temperatures below ～40 K it results from heterogenous (mobile exciton-trapped exciton) triplet-triplet annihilation. At higher temperatures it is due to homogenous triplet-triaplet annihilation. The existence of mobile excitons is also proved by the character of the ESR lines which are very narrow Lorentzians. The phosphorescence, observed only in the range 1.7–40 K, originates from at least two different kinds of traps with energies ～6 cm^?1 and ～140 cm^?1, respectively. The vibrational structure of the phosphorescence is identical to that of anthracene, with 0—0 band blue-shifted by ～400cm^?1. A kinetic model of trapping and detrapping of triplet excitons as well as the nature of the traps are discussed.     

Triplet Excitions in Crystalline Trans-Stilbene I. Spectroscopy of the So → T1 Transition

Abstract

The first singlet → triplet absorption of trans-stilbene has been studied between 10 and 300 K. The triplet exciton energy (energy of the lowest 0–0 line) is 17380 cm^?1 at 10 K, and does not change significantly with temperature. Vibrational A_g modes of 206. 1250 and 1570 cm^?1 are active. The Franck-Condon factor of the origin region is small. The low temperature spectra of the 0–0 and 206 cm^?1 regions show a doublet structure with a splitting of 82 ± 1 cm^?1 which is attributed to the site splitting. Further structure shown by the lines is discussed. The lines are approximately lorentzian. From curve fitting, line-widths and exciton-phonon coupling constants, increasing linearly with T, are deduced. Exciton-phonon coupling appears to be different on the two sites. The product of absorption coefficient at 4880 Å, α, by the total triplettriplet interaction rate constant has been measured at 295 K: αγ=2.3 ± 0.3. 10^?15 cm² sec^?1, corresponding for γ_total to a value of a few 10^?12 cm³ sec^?1.     

Assignment of the Lowest Singlet and Triplet States of the Monoaldehyde of Durene

Abstract

The monoaldehyde of durene has been synthesized. It has been shown to be the impurity frequently encountered in spectral studies involving durene crystals. Both the polarized absorption and emission spectra of the protonated and deuterated aldehyde in crystals of durene^h-14 and durene^d-14 have been obtained. Although the lowest excited singlet and triplet states, separated by 2200 cm^?1, are shown to be nπ* a number of features in the phosphorescence spectrum are more characteristic of a ³π* state. The polarization of the absorption spectrum, in particular the 0-0 band and bands involving the excitation of totally symmetric vibrations, is inconsistent with the nπ* nature of the transition. A number of explanations is proposed.     

Analyse de la Raie Zéro-Phonon et des Processus de Relaxation Excitoniques dans le Spectre d'Absorption Singulet-Triplet du Cristal de 4-4′-Dichlorobenzophenone

Abstract

In this paper we discuss the dynamic scattering information which can be obtained from an analysis, at high resolution, of the triplet exciton absorption band in the molecular crystal 4-4′-dichlorobenzophenone. The zero phonon lineshapes, widths and positions are investigated as a function of temperature. At temperatures below 30 K the broadening and the shift are analyzed in terms of exchange theory involving a torsional mode of the molecule. The lifetime in the phonon promoted state is 0.75 ps over the range 5 K-30 K. The difference between the excited and ground state energies of the torsional mode is δω = -8.45 cm^?1. Above 30 K the change on linewidth is discussed in a model which implies a momentarily localization of the exciton by lattice phonons. During the localization time a weak coupling between the trapped excitation and phonons is assumed. At very low temperatures the lineshape is asymmetric, gaussian on the high energy side, lorentzian on the low energy side. This experimental result may be due to the fact that the k = 0 level is at the bottom of the exciton band.     

Electrical Conductivity of Phenoxazine-Iodine (2:3) and Phenothiazine-Iodine (2:3) Crystals

Abstract

Single crystals of phenoxazine-iodine (2 : 3) and phenothiazine-iodine (2 : 3) salts are found to be highly conducting ([sgrave] _R.T. = 5–20 ohm^?1 cm^?1). The observed deviation from the exponential temperature dependence of the conductivities is ascribed to the degenerate semiconducting phases or alternatively to the metallic phases with impurities. However, phenoxazine-iodine and phenothiazine-iodine are perfect semiconductors below 220° K with activation energies of 0.12 eV and 0.14 eV, respectively. The absorption features related with (phenoxazine)⁺ ₂ and (phenothiazine); cations are observed in the infrared spectra of the salts.     

Time Resolved Energy Migration in an Energetically Disordered Molecular Crystalt

Time resolved emission spectroscopy is used to monitor triplet exciton migration in p-dichloro-benzene-p-dibromobenzene mixed crystals. The migration efficiency is varied by adjusting the concentration and the temperature (2–12°K). Long range migration is found even though the static energy disorder parameter W is much larger than the exciton band width B. Because of exciton tunneling, the range of the transfer is only limited by the maximum lifetime of an exciton. These results illustrate the importance of at least six key parameters in determining the efficiency of long range exciton migration; B, W, the range of transfer, the temperature, the exciton lifetime and the topology of the excitation exchange interactions through its effect on the long range connectedness of the system.     

Raman Scattering From TMTSF-Salts

Abstract

Experimental results for Raman scattering from TSeF, TMTSF-D12, (TMTSF)₂PF₆ and (TMTSF)₂AsF₆ excited with blue-green laser light at liquid nitrogen temperature are reported. A strong resonance effect for excitation of TMTSF with 4579 Å was observed and an assignment for the a_g modes was obtained by comparison with results from TTF. Methyl group modes were identified at 328 cm^?1, 472 cm^?1 and 916 cm^?1, respectively. Charging the TMTSF molecule resulted in a strong frequency shift of -122 cm^?1 and -76 cm^?1 for the a_gu₂ mode, respectively. A study of the temperature dependence of the scattering from molecular modes between 2 K and 300 K did not reveal any correlation with the phase transitions in the conducting compounds.     

Spectres de vibration du Cristal de Biphényle à Basse Température

Abstract

Low-temperature infrared and Raman spectra of Crystalline biphenyl have been investigated in the 3100–25 cm^?1 range, and those of biphenyl-D₁₀ between 200 and 25 cm^?1. The infrared dichroism of an Oriented crystal at 77°K has been measured in the 3100–400 cm^?1 region. The assignment for the internal modes V ₅(B_2u), v ₆ (B_2u), v ₁(B_1u), v ₁₀(B_1g), v ₂(B_2g) et v ₃ (B_3g) is given.

The band splitting is analized and hte components due ot the correlation effect in the fundamentals are separated from the components due to combinations. Isotopic shifts are used to assign the nine external vibrations as well as the torsional mode. The temperature effect on the frequencies occuring below 500 cm^?1 is discussed.     

Conductivity and Optical Properties of a Polyiodine Canal Complex (Benzophenone)9(KI)2I7, CHCl3

Abstract

(Benzophenone)₉(KI)₂I₇, CHCl₃ single crystals have a golden metallic reflection on the surfaces parallel to the polyiodine chain axis. The compound is a member of a large class of channel-like inclusion compounds in which isolated iodine atom chains are the only possible conducting strands in an otherwise insulating matrix. The (contactless) microwave conductivity is ～ 10 Ω^?1 cm^?1 at room temperature with an activation energy of ～0.03 eV down to 70°K, while the dc conductivity is ～10^?-⁶. Conductivity is strongly frequency dependent and contact problems are severe.     

Globular Mesogens

Abstract

Polyaniline, (4oSN) is found to exhibit a low energy absorption edge beginning near 1800 cm^?1 (ca: 0.22 eV), and a strong anion-induced absorption from about 800 to 1200 cm^?1. Electrical conductivity has an activation energy of 0.05 (15%) eV consistent with an anion-induced energy gap of about 0.1 eV.     

Properties of a-Si:H prepared by the photochemical decomposition of Si2H6

High quality a-Si:H films have been prepared by the direct photolysis of disilane at a substrate temperature below 350 °C. The growth rate is independent of substrate temperature for both undoped and phosphorus doped films, while it is thermally activated and dramatically enhanced by boron doping. The hydrogen content decreases from 7 to 2 at.%, as deposition temperature is varied from 200 to 300 °C. The photoconductivity as high as 3.7 × 10^?4 Ω^?1cm^?1 (AM1 100 mW/cm²) has been obtained and no light soak degradation was observed.     

Intrinsic and impurity infrared absorption in As2Se3 glass

A quantitative study of infrared absorption in the 250–4000 cm^?1 region of As₂Se₃ glasses doped with small amounts of As₂O₃ or purified by various procedures has been carried out with particular attention to absorption in the wavelength regions of the CO₂ and CO lasers. The dependence of the relative intensities of the oxide impurity bands in the 650–1340 cm^?1 region on the total amount of As₂O₃ added to the glass indicates the existence of three distinct oxide-impurity species. A number of higher-frequency impurity bands which are due to the presence of hydrogen in the glass and whose intensities are highly dependent on the glass-melting conditions have been observed and classified. Intrinsic multiphonon absorption in the 400–1100 cm^?1 region has been interpreted in terms of combination and overtone bands of the two highest-frequency fundamental vibrational modes. Absorption coefficients of As₂Se₃ glass in the 920–1090 cm^?1 CO₂ laser region are limited by intrinsic multiphonon absorption to values of around 10^?2 cm^?1. The lowest absorption coefficients measured in the 1700–2000 cm^?1 CO laser region were around 2 × 10^?3 cm^?1 and may contain contributions from hydrogen-impurity bands.     

Crystal growth and spectral properties of Nd3+:Ca9Gd(VO4)7 crystal

An Nd³⁺:Ca₉Gd(VO₄)₇ crystal with dimensions of ?25×30 mm³ was grown by the Czochralski method. The hardness, thermal expansion coefficient and thermal conductivity coefficient of the crystal were measured. The spectroscopic characteristics of Nd³⁺:Ca₉Gd(VO₄)₇ crystals were investigated. The absorption band at 810 nm has an FWHM of 10 nm, and absorption cross-sections are 5.81×10^?20 cm² for π-polarization and 7.47×10^?20 cm² for σ-polarization at 810 nm. The emission cross-sections at 1067 nm are 4.2×10^?20 and 6.5×10^?20 cm² for π- and σ-polarizations, respectively. The quantum efficiency η_c is equal to 94.3%. To sum up the above results, Nd³⁺:Ca₉Gd(VO₄)₇ crystal can be regarded as a highly efficient solid state laser material.     

Effect of OH-content on thermal and chemical properties of SnOP2O5 glasses

Glasses with 55–60 mol% SnO and 40–45 mol% P₂O₅ have shown extremely large differences in the chemical and thermal properties depending on the temperature at which they were melted. Glasses prepared at low melting temperature, 450–550 °C, had low T_g, 150–200 °C, and low chemical stability. Glasses prepared at high melting temperature, 800–1200 °C, had much higher T_g, 250–300 °C, and much higher chemical stability. No significant differences were found by ¹¹⁹Sn Mössbauer and ³¹P Nuclear Magnetic Resonance spectroscopy. Large differences in the OH-content could be detected as the reason by infrared absorption spectroscopy, thermal analyses, and ¹H Nuclear Magnetic Resonance spectroscopy. In samples with low T_g, a broad OH – vibration band around 3000 nm with an absorption intensity >20 cm^?1, bands at 2140 nm with intensity ～5 cm^?1, at 2038 nm with intensity ～2.7 cm^?1, and at 1564 nm with intensity ～0.4 cm^?1 were measured. These samples have shown a mass loss of 3–4 wt% by thermal gravimetric analyses under argon in the temperature range 400–1000 °C. No mass loss and only one broad OH-band with a maximum at 3150 nm and low absorption intensity <4 cm^?1 could be detected in samples melted at high temperature, 1000–1200 °C, which have much higher T_g, ～300 °C, and much higher chemical stability.     

High field effects in amorphous germanium

Measurements of high field current have been made on amorphous Ge (a-Ge) films over the temperature range from 100 to 300 K. Non-ohmic conduction in a-Ge occurs at electric fields greater than 1–2 × 10⁴ V/cm. Field dependence of the conductivity has been explained in terms of the enhanced emission probability of carriers from the screened coulombic trap centers. Assuming the optical dielectric constant for a-Ge films, the screening length of the trap centers and the density of states at the Fermi level are estimated to be 12 Å and ～6.1 × 10²⁰ cm^?3 eV^?1, respectively.     

The effects of oxygen,hydrogen and fluorine on the conductivity of high purity evaporated amorphous silicon films

Electron bombardment evaporation was used to deposit amorphous silicon (α-Si) films in an evaporator with a base pressure of 2 × 10^?10 Torr. Rutherford backscattering analysis was used to establish the conditions necessary for deposition of pure films.The DC conductivity was measured as a function of temperature (? 150°C to + 140°C). Pure films, which were deposited between room temperature and 400°C, were found to have a room temperature conductivity (σ_RT) in the region of 10^?3μ^?1cm^?1 and a log $\text{σα}\text{T}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$ dependence. The value of σ_RT could be reduced by annealing reaching a minimum of 2 × 10^?7μ^?1 cm^?1 for an anneal temperature (T_A) of 520°C, but activated conduction was not observed.The implantation of hydrogen or fluorine (or contamination with oxygen) had the effect of reducing σ_RT, with a minimum value of less than 10^?8μ^?1cm^?1 (T_A = 400°C) for fluorine implantation to a dose of ≈ 10¹⁶ cm² (≈ 0.4 at% concentration). These films had high temperature (50°C) activation energies typical of activated conduction in extended states on the edge of the mobility gap. Implantation of fluorine to a dose of 1.5 × 10¹⁷ resulted in a rise of σ_RT (T_A = 400°C) to nearly 10⁴μ^?1 cm^?1 and log $\text{σα}\text{T}{}^{\mathrm{<mtext>?1</mtext><mtext>4</mtext>}}$ behaviour.X-ray analysis revealed that some crystallization occurred in films annealed at 600°C. This is correlated with a rise in σ_RT of the pure films and the disappearance of the effects of the introduced impurities.     

Laser excitation dependent nonlinear absorption of 2-Amino 5-Nitropyridinium dihydrogen phosphate

Abstract

Laser excitation and intensity-dependent third-order nonlinear optical (NLO) absorption properties of 2-amino 5-nitropyridinium dihydrogen phosphate (2A5NPDP) in both pulsed (532?nm, 5?ns, 100 µJ) and continuous wave (532?nm, 50?mW) regime were studied by Z-scan experiment. Under CW laser excitation, 2A5NPDP exhibits saturable absorption (SA) ascribed to be of thermo-optic origin. Interestingly the sample show reverse saturable absorption (RSA) due to genuine two-photon absorption (2PA) process under nano pulsed laser excitation. Earlier thermodynamic properties such as thermal conductivity (51?W/m.K), specific heat capacity (3894?J/Kg.K) and thermal diffusivity (7.5?×?10^?6 m²/s) were estimated theoretically from the DSC curves. Thus 2A5NPDP with excellent thermal stability and high NLO coefficients can be utilized as an energy-absorbing optical limiter and saturable absorber under nano pulsed and CW green laser excitation.     

Synthesis,conductivity, and the crystal structure of a new stable metal, β″-(<Emphasis Type="Italic">DOEO</Emphasis>)<Subscript>2</Subscript>HSeO<Subscript>4</Subscript> · H<Subscript>2</Subscript>O

The stable metal β″-(DOEO)₂HSeO₄ · H₂O I) based on a new donor compound, 3,4-(1,4-dioxanediyl-2,3-dithio)-3′,4′-ethylenedioxo-2,5,2′,5′-tetrathiafulvalene] (DOEO), is synthesized and structurally characterized for the first time. The synthesis is performed by the electrocrystallization technique (direct current density j = 2 × 10^?6 A/cm²). The crystals are triclinic, and the unit cell parameters are as follows: a = 5.495(1) Å, b = 9.715(2) Å, c = 16.878(3) Å, α = 83.52(3)°, β = 82.54(3)°, γ = 73.51(3)°, Z = 1, and space group \(P\bar 1\). The salt has a layered structure. The DOEO^1/2+ radical cation layers are aligned parallel to the ab planes. The HS_eO ₄ ^? · H₂O solvated anions are located in channels along the a axis and are disordered over two positions near the center of symmetry (1/2 0 0) with a probability of 50%. The conductivity of the salt is equal to 300–400 Ω^?1 cm^?1 at room temperature and increases upon cooling to the boiling point of liquid helium (4.2 K) by a factor of 100–200 depending on the sample.     

The optical constants of quartz,vitreous silica and neutron-irradiated vitreous silica (I)

The infrared reflectivity of three forms of silica, α-quartz, vitreous silica and neutron-irradiated vitreous silica (≈ 2.7 × 10²⁰ neutrons cm^?2) has beenmeasured from 400–2000 cm^?1. These data have been analysed by a Kramers-Kronig transform to give the real and imaginary parts of the complex dielectric constant. Considerable care has been taken to identify and minimize errors arising in the measurements of the reflectivity spectra and in the subsequent analysis. Data are presented for the optical constants, oscillator frequencies, band strengths and halfwidths of each band. The spectra for vitreous silica and neutron-irradiated silica show two regions of absorption which are not present in the crystalline form — a strong band is observed near 950 cm^?1 and a broad band from 600–800 cm^?1. A difference spectrum obtained by subtracting the spectrum of the imaginary part of the dielectric contrast for vitreous silica from the corresponding data for neutron-irradiated silica reveals more detailed structure in the form of a weak but sharp band at 620 cm^?1. Interpretation of these results is contained in a companion paper.     

Infrared spectra of glassy Se containing small amounts of S,Te, As,or Ge

The infrared transmission spectra of glassy Se containing 2.5 and 5.0 at % S, Te, As or Ge as well as pure Se were measured in the wavenumber region 400-60 cm^?1 at room temperature. Besides the absorption bands reported already for pure Se, well-defined bands were founds at 355 cm^?1 and 168 cm^?1 for the addition of S, and at 205 cm^?1 for Te. These new absorption bands attributed to Se₃S₅ and Se₅Te₃ mixed rings, respectively. For As, a strong absorption band appeared at 240 cm^?1. The band near 135 cm^?1 began to broaden and shift to lower frequency with As content. Two shoulder bands near 307 cm^?1 and 278 cm^?1 and a separated band at 195 cm^?1 were found for Ge. With increasing Ge concentration the band at 135 cm^?1 broadened and shifted to lower frequency. An interpretation for the new bands is presented on the basis of a molecular model.