Absorption spectra of NaCl: Pb2+ at the A-band region

The origin of the absorption spectrum of NaCl:Pb²⁺ at the A-band region has been investigated. Main peaks are observed at 265, 273 and 290mμ in an untreated sample. In addition to the effect of lead concentration and thermal treatments, the luminescence and excitation spectra associated to the various bands have been determined. It is concluded that the 290 mμ band should be a composition of a number of bands corresponding to different types of simple dipole aggregates. The 265 mμ band, as well as the structure appearing in the region 220–260 mμ, is consistent with the existence of PbCl₂ precipitates.     

Luminescent properties of LiCl-Cu single crystals

The absorption, photoluminescence, x-ray luminescence, and thermoluminescence spectra, and the photoluminescence excitation spectra of LiCl-Cu single crystals with different activator concentration were investigated at temperatures of 79–450°K. The absorption spectrum at room temperature has two bands with maxima at 237 and 259 nm. The absorption coefficient of the 237 nm band is proportional to the copper concentration in the crystal (C_Cu ≤ 7·10^?4 mole %). The photoluminescence and x-ray luminescence spectrum at room temperature consists of one emission band at 324 nm, which conforms with the Mollwo-Ivey rule in the homologous series RbCl → KCl → NaCl → LiCl. The copper ions create trapping levels for electrons and holes at different depths in the forbidden band of the LiCl crystal. The correlation between the thermoluminescence peaks and the recombination-luminescence excitation bands (infrared stimulation) is investigated.     

Absorption,excitation and fluorescence spectra of thallium activated cesium bromide

Absorption, excitation and fluorescence spectra of T1⁺ doped cesium bromide have been investigated at various thallium concentrations. At very low thallium concentration two absorption bands are obtained at 225 nm and 264 nm. With rise of thallium concentration additional absorption bands are obtained at 230, 244, 258, 270 and 285 nm. A single bell-shaped fluorescence band at 357 nm in the ultraviolet region is obtained at low thallium concentration. Two additional visible fluorescence bands appear at 440 and 540 nm with rise in thallium content. The excitation spectra for ultraviolet emission band and visible emission bands are found to be different. Accordingly the ultraviolet emission band is attributed to the characteristic A emission in T1⁺ ion and the visible bands are attributed to dimer centers havingD _4h site symmetry.     

Optical properties of Cu+ centers in NaCl

Different aggregation-precipitation states of Cu⁺ have been characterized by absorption bands peaked at 305, 350 and 372–383 nm.The absorption bands at 372–383 nm, observed exclusively in the most doped crystal, have been associated with the Z₁₂, Z₃ excitons of CuCl microcrystals incorporated into the NaCl matrix Their positions shift to low energies with increasing concentration, as expected for a decrease in the stress over the precipitate.The Z1₁₂, Z₃ exciton bands of CuCl microcrystals precipitated in NaCl can be observed by the optical absorption spectrum without reaching saturation Therefore, this technique could be an alternative method to studies of CuCl thin-film depositions or reflectivity of CuCl single crystals.The red emission band observed at 600 nm is a long-lived emission (τ? 29 ms) at variance with the behavior reported for the Cu⁺ emission It is related to energy transfer processes from Cu⁺ to Mn²⁺.     

über die optische Absorption von Schichten aus PbCl2 und des Systems TlCl-KCl

In the first part of this paper the optical absorption of amorphous films of PbCl₂, formed by quenching condensation, is shown and compared to the spectrum of PbCl₂ in its normal state. The sharp exciton band of crystalline PbCl₂ in the long wavelength region is considerably broadened in the spectrum of amorphous films. The transition from the amorphous state to the normal crystalline state is indicated by an abrupt, irreversible change in the absorption curve at 260? K. This comparatively high temperature of crystallisation seems to be due to the complicated structure of PbCl₂. In the second part of this paper the optical absorption curves of evaporated films of the system TlCl-KCl are measured. A shift of the absorption bands as a function of the composition is found. The 3,46-eV-maximum of pure TlCl is coordinated to the A-band of the KCl∶Tl-phosphor. On the other hand there is no connection between the 5,82-eV-maximum of TlCl and the known bands of KCl∶Tl.     

The 404.5-nm system of the ReO molecule

Observations on the emission spectrum of ReO in the region 375–870 nm are reported. Five bands of a $\text{ΔΩ}\text{= 0}$ system with (0, 0) band at 404.5 nm have been rotationally analyzed and the principal results for ¹⁸⁷ReO are (in cm^?1) ν₀ = 24 709.90, B′_e = 0.3819, B″_e = 0.4252, ω′_e = 874.8₂, and $\text{Δ}\text{G″(}\text{1}\text{2}\text{) = 979.1}{}_2$. Data on the minor isotopic species ¹⁸⁵ReO are also reported. It is suggested that broad rotational profiles found in bands near 842 nm may be due to nuclear hyperfine structure.     

Calcium precipitation in NaCl monitored by the Eu2+ -fluorescence

Taking into account that the optical spectroscopy of the Eu²⁺ ion is quite sensitive to the crystalline environment in which this ion is located, in the present investigation the fluorescence of a small concentration (8 ppmm) of divalent europium incorporated into a NaCl crystal which was also doped with ≈4500 ppmm of Ca²⁺ has been systematically investigated as a function of different thermal treatments in order to study the calcium-precipitation processes in the host NaCl. The data presented in this paper strongly suggest that the annealing of quenched samples at 200°C produces the incorporation of Eu²⁺ into the stable dihalide phase CaCl₂, as well as into the metastable precipitated CaCl₂-like plate zones parallel to the {111} planes of the NaCl matrix. This fact is associated with the increase in intensity of two overlapping emission bands peaking at 430 and 432 nm. On the other hand, the aging of quenched samples at room temperature produces the growth of three emission bands peaking at 400, 414, and 447 nm. The former two emission bands have been associated with Eu²⁺ embedded into calcium precipitates, the structures of these precipitates being different from that of CaCl₂, while the band at 447 nm has been ascribed to europium ions incorporated into the metastable precipitated CaCl₂-like plate zones parallel to the {310} planes of the NaCl matrix. Some of the characteristics of the different calcium second phase precipitates have been obtained by measuring the crystal field splitting (10 Dq) of the 4f⁶5d configuration of the divalent europium ions when they were located inside them. Values for the 10 Dq splitting were determined from the excitation spectrum of each of the emission bands associated with the different calcium-precipitated phases.     

Photoluminescence from surface states in MgO and CaO powders

Photoexcitation spectra of luminescence from activated MgO and CaO powders have been obtained over the wavelength range 120–300 nm at sample temperatures down to 10 K. These spectra show broad features attributable to electronic transitions of O^2? ions in coordination states varying from 6-fold (bulk ions) to 3-fold. O^2? ions in 4 and 5-fold coordination contribute a broad inhomogeneously broadened spectral feature centered at 225 and $\text{\$}\text{?}$250 nm in MgO and CaO powders, respectively. This feature is interpreted as a surface exciton band well separated in energy from the bulk exciton band at 160 and 180 nm, respectively. An interaction between discrete bulk exciton levels and these surface bands yields dispersion-like structure superimposed on the broad surface photoexcitation bands.     

The visible and photographic infrared spectrum of osmium oxide

The emission spectrum of OsO has been photographed in the region 405–875 nm where many new bands have been observed. In favorable cases the ${}^{190}\text{OsO}{}^{192}\text{OsO}$ isotopic splittings have been resolved and aid in vibrational assignments. Three visible bands in the region 433–470 nm have been assigned as (1,0), (0,0), and (0,1) of a $\text{ΔΩ}\text{= 0}$ electronic transition. The (0,0) and (0,1) bands have been rotationally analyzed, yielding principal constants (cm^?1) for the visible system of ν₀ = 22 273.3, B′₀ = 0.3657, D′₀ = 2.8 × 10^?7, B″_e = 0.4023, D″_e = 3.2 × 10^?7, $\text{Δ}\text{G″(}\text{1}\text{2}\text{) = 780.7}$, and $\text{Δ}\text{G″(}\text{1}\text{2}\text{) = 884.9}$. A band at 825.4 nm has been found to be a $\text{ΔΩ}\text{= +1}$ (0,0) band with the same lower state as in the analyzed visible bands. Constants for the upper state of the ir system are ν₀ = 12 109.7, B′₀ = 0.3845, and D′₀ = 3.1 × 10^?7 cm^?1.     

Emission spectra of KBr:Sn2+

Crystals of KBr:Sn²⁺ irradiated in the A₁, A₂, B or D absorption bands exhibit strong emission in the region of 500 nm. The dependence of this emission on excitation wavelength in the A absorption band shows the 500 nm emission band to be a doublet. This doublet structure is due to electrostatic perturbation from a nearby cation vacancy. It is not possible from emission spectra alone to decide on the actual symmetry of the A_T1 and A_T2 centres responsible for the emission doublet but the various possibilities are discussed. Quenching experiments show that a small emission band at 700 nm is due to Sn²⁺ dimer centres. A series of weak emission bands on the high-energy side of the A_T band are ascribed to emission from the relaxed excited B and D states.     

Cathodo-luminescence spectra of alkali halides

Cathodo-luminescence spectra of fourteen alkali halides and of some mixed crystals of NaCl and KCl have been studied. The spectra show broad structureless bands. In some ten halides it is possible to find a strong band whose peak position shifts towards longer wavelengths as the inter-atomic distance increases. For pottasium halides the relationship λ_max=1380d, where “d” is the inter-atomic distance, holds approximately but is not generally true. A mechanism of cathodo-luminescence in alkali halides has been postulated, and an interpretation of the above band and of some NaCl bands has been made on that basis.     

Absolute determination of electronic band structure of copper by angle-resolved photoemission

Structures in the angle-resolved photoemission spectra from copper in the (1$\text{1}$0) and (001) mirror planes at fixed photon energy hν as a function of emission angle show discontinuities in energy position or slope as function of emission angle. These discontinuities are due to the appearance of specific interband transitions on zone boundaries. The appearance angle allow the absolute determination of momentum $\text{k}$ of the transition. E($\text{k}$) points have been determined for most d-bands and several conductions bands. Experimental data are in good agreement with Burdick's band calculation, as also are the E($\text{k}$) points which have been determined using the energy coincidence method.     

The origin of 3.55 eV emission band of RbCl:Tl

Fluorescence spectra of KCl:Tl, RbCl:Tl and NH₄Cl:Tl under A band excitation at room temperature (300 K) and liquid nitrogen temperature (77 K) have been re-examined in order to ascertain the origin of the 3.55 eV emission band of RbCl:Tl. The emission band at RT is found to show two components and the weaker component becomes dominant at LNT. The observations are explained in terms of Patterson's model of two local environments for Tl⁺ ion. One of them is a Tl⁺ having local CsCl like environment. The 3.55 eV emission band at 300 K is assigned to electronic transition in the Tl⁺ having local CsCl like environment.     

Optical absorption spectrum of hematite, αFe2O3 near IR to UV

Optical absorption spectra have been measured on thin (011) single crystal platelets and on highly oriented (110) thin films of αFe₂O₃. We have observed and assigned some of the absorption bands predicted by ligand field theory and SCF-Xα calculations. The temperature dependence of the 11760 cm^?1 single crystal band has been fitted to the function $\text{? = ?}{}_0\text{(1 + exp (?}\text{θ}\text{T}\text{))}$ with $\text{?}{}_0\text{= 0.85 × 10}{}^{\mathrm{?4}}$ and θ = 200 K (139 cm^?1). We have measured the photocurrent as a function of wavelength and have found several peaks that coincide with optical absorption bands.     

The UV,blue and green up-conversion luminescence of PbF2+GeO2:Er2O3 pumped with 650 nm

A detailed study of the spectroscopic properties of the PbF₂+GeO₂:Er₂O₃ vitroceramic sample upon 650 nm excitation was investigated. The absorption, emission, excitation spectra, and time-resolved spectra have been measured. The up-conversion of red radiation (650 nm) into UV (368 nm and 379 nm), blue (406.8 nm) and green (522 nm and 540 nm) emissions is observed for Er³⁺ ions in the sample. The up-conversion process involves a two-photon absorption for the violet, blue, and green emission bands. A three-photon process happens for another violet (379 nm) band.     

Resonance Raman effect in thiourea

Raman spectra of thiourea have been observed in H₂O and D₂O solutions with the exciting laser beams of 514.5, 488.0, 457.9, 363.8, 325.0, and 257.3 nm. The resonance Raman excitation profile of the 729-cm^?1 line has been examined in the region of the 237-nm absorption band ($\text{π}{}_{\mathrm{<mtext>CS</mtext>}}{}^1\text{← π}{}_{\mathrm{<mtext>CS</mtext>}}$) by use of a solvent shift of the absorption band instead of by changing the wavelength of the exciting beam. The depolarization degree of this line was measured and its overtone Raman line was also observed. On the basis of the results of these experiments, it has been concluded that the 729-cm^?1 Raman line, assignable to the CS stretching vibration, derives its intensity solely from the 237-nm band when it is excited at 257.3 or 325.0 nm. On exciting in the region 363.8–514.5 nm, however, contributions of the higher-frequency bands are predominant rather than the contribution from the 237-nm band. The Raman line at 1520 cm^?1 of thiourea-d₄ is assignable to the NCN antisymmetric stretching vibration. From its excitation profile, its intensity has been considered to come from a vibronic coupling between the excited electronic states of the 220-nm ($\text{π}{}_{\mathrm{<mtext>CS</mtext>}}{}^1\text{← π}{}_{\mathrm{<mtext>N</mtext>}}\text{? π}{}_{\mathrm{<mtext>N</mtext>}}$) and the 197-nm ($\text{π}{}_{\mathrm{<mtext>CS</mtext>}}{}^1\text{← π}{}_{\mathrm{<mtext>N</mtext>}}\text{+ π}{}_{\mathrm{<mtext>N</mtext>}}$) bands.     

Interpretation of electronic spectra by configuration analysis: Absorption spectra of monosubstituted naphthalenes

The electronic absorption spectra of four monosubstituted naphthalenes, α-, β-naphthols, and α-, β-naphthylamines have been investigated by means of configuration analysis with particular attention to the dependence of spectra on the position of substitution and on the electron-donating power of the substituent. The results of molecular orbital calculations based on the Pariser-Parr-Pople method are analyzed in terms of locally excited states and intramolecular charge-transfer configurations. The characteristic changes in location and polarization of the L_b, L_a, and B_b bands caused by substitution at the α- or β-position are adequately explained by the analysis. Two strong absorption bands of α-substituted naphthalenes, which appear in place of the B_b band of naphthalene, are shown to result from a mixing of the $\text{B}{}_{\mathrm{3u}}{}^{\mathrm{+}}\text{(B}{}_{\mathrm{b}}\text{)}$ and $\text{A}{}_{\mathrm{g}}{}^{\mathrm{?}}$ states. The amino group exerts a great influence on the electronic structure of the parent molecule, so that the B_b band cannot be identified in the spectrum of β-naphthylamine.     

On the origin of the visible emission in KBr:Tl and KCl:Tl crystals

The intensity of the visible emission of KBr:Tl at 440 nm is shown to increase linearly with the absorption in the A₁ band at 4.64 eV (267 nm). The latter band increased with the square of the Tl⁺ ions concentration, which supports its assignment to thallium dimers. Similarities in behavior between the 440 nm emission of KBr:Tl and the 475 nm emission of KCl:Tl suggest that the latter is also related to dimers. This is supported by the superlinear dependence of this emission on the Tl⁺ ion concentration. Deviations ofthe superlinearity from the square dependence expected for dimers is explained by the overlap between the weak dimer absorption and the very strong A-band.The 440 nm emission of KBr:Tl was found to be excited only in the A₁ component of the dimer absorption and not in the stronger A₂ component. This indicates that the emission process may be compound.     

Photoemission from single crystal xenon

Normal exit photoemission spectra from the (111) surface of a xenon single crystal indicate that the valence level emission is considerably broader than expected on the basis of band structure calculations. Similar observations from polycrystalline samples have lead Parrinello $\text{et al}$ to propose an excitonic screening mechanism which would cause an apparent increase in the spin-orbit splitting at the Γ point. The details of the spectra reported here show, however, that the effect could simply be due to a dispersion of the bands stronger than that predicted theoretically. Anomalous intensity effects at $\text{h}\text{?}\text{ω = 21.2}\text{eV}$ are explained in terms of electron-electron scattering.     

Luminescence spectra of lead-doped NaCl,KCl and KBr

The luminescence spectra of lead-doped NaCl, KCl and KBr have been systematically investigated. Special attention has been paid to the effects of concentration and thermal history of the crystals. In the three systems, the emission spectra for A and C band excitation consists mainly of two well-defined emission bands whose energy separation is ～0.7 eV. It has been concluded that none of the bands can be attributed to a single type of lead center but are both typical of Pb²⁺ luminescence. In fact, their behavior can be correlated with that found for most monovalent ions and interpreted in a similar way. The excitation spectra for the two emissions have shown that the A-band is complex. One of the components appearing in very low doped and quenched samples is ascribed to dipoles, whereas additional side bands are attributed to complexes or small aggregates involving Pb²⁺ ions.