A spectroscopic study of the intermolecular photodimerization of 1-(9-anthryl)-3-(1-naphthyl)propane

Single crystals of the intermolecular photodimer of 1-(9-anthryl)-3-(1-naphthyl)propane have been prepared. The photophysical properties of this molecule as well as the sandwich dimer obtained by photocleavage in methylcyclohexane at 77 K have been recorded. A qualitative study of the photochemical properties of the sandwich dimer in single crystals of the photodimer host shows that the photochemical mechanism is similar to those of the anthracene sandwich pair and the anthracene-naphthalene pair.     

Electronic spectroscopy of Se2- in KBr

Rapid quenching of KBr crystals doped with Se^2- gives isolated Se^2- ions which are strongly luminescent. Two emission spectra were observed, one with a maximum intensity at about 14100 cm^-1 and the other with a maximum intensity at about 17200 cm^-1. Only the red emission is observed by excitation into the lowest energy absorption band at 24600 cm^-1, while between 10 K and about 150 K both red and yellow emissions are observed by excitation into the second absorption band at 26770 cm^-1. Both are assigned to the isolated Se^2- center in different distorted charge transfer states. The yellow emission is observed below about 100 K, reaches maximum intensity at about 35 K and is absent below 10 K. There are complementary changes in the intensity of the red emission so that the sum of the two emission intensities is constant. The absorption spectra of the isolated Se^2- and the (Se^2--vacancy) pair have been identified as well as the spectrum of a cluster of two or more (Se^2--vacancy) pairs.     

External heavy atom effect on the emission of carbazole

External heavy atom induced quenching of luminescence emission of carbazole in n-hexane and methylcyclohexane in the presence of chloro- and bromoacetic acids at 300 K and 77 K is described. A straight line relation between fluorescence quenching rate constant and the acid dissociation constant of chloroacetic acids, which is related to electron affinity, is observed. Different photophysical parameters at 77 K of unperturbed and perturbed fluorescent carbazole in ternary solutions have been determined and suitable reaction mechanism for quenching has been proposed. Inference has been drawn about complex formation in the triplet state of carbazole from the biexponential nature of the phosphorescence decay curve.     

Structural effects on intramolecular exciplexes of 1-amino-3-anthryl-(9)-propanes

The photophysical behavior of six 1-(N-aryl-N-alkyl)-amino-3-anthryl-(9)-propanes was studied by steady-state and time-resolved fluorescence measurements in methylcyclohexane/ isopentane (MP). Structurally, these compounds are most suitable for the formation of intramolecular exciples as shown by the high exciplex quantum yields. The rate constants and the activation energies show that the rate of the exciplex formation depends on steric effects of the N-alkyl group and on the donor effect of the N-aryl group. From the rise curves of the exciplex emission it follows that also in nonpolar solvents exciplexes with a conformation deviating from the favored sandwich structure can be formed. The solvent effect on the fluorescence properties was investigated.     

Studies of radical pairs in potassium hydrogen malonate I. E.S.R.

Irradiation of single crystals of potassium hydrogen malonate with X-rays at 77 K yields two types of radical pairs, which differ in the orientation of the vector r linking the radicals of a pair but are composed of the same monoradicals. This monoradical is the main radical species found at room temperature and is characterized by hydrogen abstraction from the methylene group. Each type of pair exists in three modifications with respect to the fine structure parameters D and E, depending on the temperature treatment of the crystals after irradiation. The principal values of the dipole splitting tensor and the direction cosines of r for all pairs were determined. By application of the appropriate theory the signs of D and E could be deduced from second order effects observed at 9·5 GHz and 35 GHz. The two types of pairs exhibit marked differences in their fine structure parameters, their microwave saturation and their temperature and light stability, all of which can be attributed to different orientations of the linking vectors r relative to the molecular planes. Finally temperature coefficients of the dipole interactions were measured yielding opposite signs for the two types of pairs.     

Photoluminescence in powdered crystalline GeSe2

The decrease of photoluminiscence (PL) intensity under continuous excitation in powdered crystalline GeSe₂ was observed at 77 K. The intensity of PL decreased by ～ 50 % in 2.10³s. The characteristics of the PL band for the powdered samples at 77 K are identical with those for crystals, but the temperature dependence of the PL intensity and the peak of the PL spectrum in the temperature range 77–200 K for powdered and bulk crystalline samples are different.     

Optical properties of Tm-doped GaSe single crystals

Optical properties of Tm-doped GaSe single crystals were investigated by measurements of optical absorption and photoluminescence. The single crystals were grown by the Bridgman technique. The X-ray diffraction analysis revealed that the single crystals were in the ε-type GaSe phase. The optical absorption spectra showed a sharp absorption peak at 582 nm near the band edge, which is due to direct free exciton. The temperature dependence of the energy of the exciton absorption peak was well fitted by the Varshni relation. In the photoluminescence spectrum at 10 K, we observed a very weak emission peak at 586 nm, a relatively strong emission peak centered at 613 nm, and several sharp and narrow emission peaks in the 790-840 nm region. The two emission peaks at 586 and 613 nm were associated with intrinsic emission lines due to direct free exciton and indirect bound exciton. The emission peaks in the 790-840 nm region, which were related to extrinsic emission, were assigned as due to the ³F₄→³H₆ transition of Tm³⁺ ions with a low symmetry of D₃ in the host lattice.     

Investigation of the optical absorption and emission spectra of CdCl2: Ni2+ single crystals

The optical absorption, emission, and excitation spectra of CdCl₂: Ni²⁺ single crystals are investigated. The absorption bands around 19,200 cm^-1 are reassigned and a few new bands above 22,000 cm^-1 are observed and assigned to singlet states. The emission bands at 77 K are examined in more detail and the previous assignments seem to be not correct.     

Impurity absorption and luminescence of CuGaSe<Subscript>2</Subscript> crystals

A comparison of the experimental and calculated absorption spectra of CuGaSe₂ crystals revealed the existence of two acceptor levels with ionization energies of 66 and 167 meV in the samples under study. It was found that the luminescence spectra of CuGaSe₂ measured at 77 K exhibit four impurity-band transitions with impurity ionization energies of 66, 99, 136, and 190 meV. An analysis of the temperature dependence of the luminescence intensity in the temperature range 11–77 K revealed a band peaking at 1.671 eV due to the radiation of donor-acceptor pairs. The calculated sum of the ionization energies of the impurities responsible for the formation of donor-acceptor pairs and the temperature dependence of the relative intensities of impurity-band emission were used to determine the ionization energies of the corresponding donor and acceptor.     

ZnSe晶体中Cu杂质深能级的ODLTS谱

用控制Cu杂质在ZnSe品格中占据位置的方法,成功地得到了Cu-G和Cu-R中心分别占优势的ZnSe:Cu晶体.首次用ODLTS方法测得与Cu-R和Cu-G中心相应的受主能级分别位于价带顶上0.72eV和0.30eV.     

The vibrational structure of the electronic spectra of quinoxaline in shpolskii-type hydrocarbon matrices

Quasilinear spectrum of the S₁(n, π¹, ¹B₁) ← S₀ transition of quinoxaline in crystalline methylcyclohexane matrix and quasilinear phosphorescence spectra of quinoxaline in high- and low-temperature modifications of isooctane matrix were obtained at 77 K. The results of a full vibrational analysis of the spectra are presented and discussed. The diffuseness of the absorption spectrum in the range 3200-2900 Å is ascribed essentially to a small energy gap between the S₂ and S₃ states. The activity of out-of-plane vibration, 865 cm^-1, in the phosphorescence and the influence of matrices on the structure of the spectra suggest the possibility of out-of-plane distortion of the quinoxaline molecule in the T₁ state.     

Hydrogen bonding,polarity and matrix effects on the spectroscopic and photophysical properties of some N- and 3-substituted derivatives of carbazoles

Fluorescence spectra and photophysical properties of N-cyano and N-carboethoxy carbazole derivatives have been compared to the equivalent 3-substituted compounds in fluid polar and unpolar solutions and in a low temperature rigid matrix at 77 K. The 3-carboethoxy derivatives have been shown to form an excited state complex (exciplex) with ethanol in fluid solutions. On the other hand the photophysical properties of the N-substituted derivatives are much affected by the solvent polarity in fluid solutions in that the radiationless decay rate constants show a marked increase in these media. A tentative explanation has been given in terms of the relative energy gap existing between the ¹L_b and the ¹L_a states of these molecules.     

Luminescence centers in phosphorus-doped Cd1−xMgxTe mixed crystals

The emission and excitation spectra of P-doped Cd_1?xMg_xTe (x ? 0.45) mixed crystals have been measured over the temperature range of 300 ～ 4.2 K to reinvestigate the photoluminescence process of two broad emission bands; the 690 nm band of the as- grown crystals and the 610 nm band of the annealed crystal. The excitation spectrum of each band has a characteristic peak at 550 nm near the absorption edge of this crystal. Together with the data of the decay characteristic and the halfwidth of each band, we discuss the difference in the recombination process when the crystal is excited under two different radiation at 365 and 570 nm (close to the 550 nm radiation). It is concluded that both emission bands arise from donor-acceptor pairs and a localized center or self- activated center; the associated pair is V_Cd-interstitial P in the as-grown and V_Te ? P_Te in the annealed crystal.     

Excimer emission of crystalline naphthalene

Excimer emission of naphthalene has been observed in microcrystals obtained by grinding single crystals mechanically and in evaporated films. The emission spectrum of the excimer in the microcrystal was equal to that in the evaporated film. The decay times of both excimer emissions were about 140 ns at 77 K. The temperature dependence of these decay times has been interpreted by the distribution of the excimers in thermal equilibrium between two vibrational states.     

Temperature dependence of EPR spectrum of Mn2+ doped in ammonium iodide single crystals

EPR of Mn²⁺ doped in ammonium iodide single crystal has been studied at X-band in the temperature range 573–577 K. The observed temperature dependence of line widths and spin Hamiltonian parameter b₂⁰ below room temperature is related to the structural transformations in the crystal. The coexistence of high temperature phase (NaCl) and low temperature phase (CsCl) is attributed to the large thermal hysteresis in line widths and b₂⁰. The dissociation of ion vacancy pairs occurs near 500 K and is reflected in the reversible change of an anisotropic EPR spectrum in an isotropic sextet near this temperature. The ion vacancy pair models for NaCl and CsCl phases are discussed along with the effects of thermal processing of the samples. Heating the crystals above 500 K leads to expulsion of Mn²⁺ impurity from the crystal.     

X射线辐照后BaFC1中缺陷性质的研究

未掺Eu2+的BaFCl粉末样品在80K下经X射线辐照后,在不同的温度条件下(从80K副273K),用580nm的光波激励样品时观测到310nm和380nm的发光峰.经分析认为,样品经X射线辐照后,在晶体中形成两种卤素离子的F-H''心对.当用F心吸收带的光波激励样品时,两种F—H心对衰变成相应的自陷激子态并复合发光.310nm和380nm分别对应于F-离子和Cl-离子的自陷激子的发光,并且它们的发光强度强烈地依赖于温度的变化。     

Luminescence properties of BaWO4 single crystal

UV excited photoluminescence from BaWO₄ (BWO) single crystals has been investigated in the temperature range of 77-300 K. The presence of two emission bands in the UV and blue spectral regions is observed under excitation by 230 nm at room temperature. The observation of UV emission band at room temperature is a novel result. The thermal treatment at elevated temperatures under air or vacuum is observed to influence the optical and luminescence properties of the crystal. The changes brought about by annealing in air are found to be reversible. However, in vacuum annealed samples the UV emission is completely quenched.     

Injection of the edge electroluminescence in ZnSe MOS diodes

Injection luminescence and related properties of metal-ZnO-ZnSe-metal tunnel diodes are described. The edge emission of ZnSe is studied in the temperature range 30-300 K with respect to: a) band shape b) coupling strenght parameter, c) time resolved spectra and d) temperature dependence.External quantum efficiecies of the blue band of 2.61 × 10^-5 have been observed at 77 K. The lowest voltage threshold observed for blue band emission is 1.5 V.The relation between the electroluminescence and electrical characteristics of the MOS diodes are discussed.     

Physical and Optical Properties of Calcium Zinc Borophosphate Glasses Doped with Manganese Ions

This article reports on the physical and optical properties, absorption, and luminescence spectra in the visible region, of calcium zinc borophosphate glasses doped with manganese ions. The manganese composition was varied up to 10 mol%. The aim of this work was to investigate the effect of the luminescence properties when the glasses were doped with different compositions of manganese ions. X-ray diffraction profiles confirmed their glassy nature. The optical absorption spectrum showed bands characteristic of manganese ions in octahedral symmetry. Both excitation and emission spectra were recorded for these glasses to understand their optical performances. The emission spectrum showed a single broad band (green region) in octahedral symmetry at 582 nm as a result of transition from the upper ⁴T_1g state to the ⁶A_1g ground state of manganese ions. As the concentration of manganese ions increased, the emission band increased from 582 nm (green-light emission) to 650 nm (red-light emission). Apart from the spectral analysis, different physical properties of these glasses were also analyzed. Based on the physical and optical properties, we found the samples to be more promising for their use as novel luminescent optical materials.