Emission and decay time studies on Pb2+ centers in KBr,RbBr, and RbCl

The emission spectra and the luminescence decay times of KBr, RbBr, and RbCl crystals doped with Pb²⁺ and excited in the A-absorption band have been studied in the temperature range 5–300 K. The emission-lineshape spectra have been analysed in terms of skew-Gaussian bands. New bands have been observed in RbCl and RbBr at very low temperatures. While the luminescence decay of KBr:Pb²⁺ and RbBr:Pb²⁺ show only a single component with a decay time τ ～ 20 ns, RbCl:Pb²⁺ shows a short and a long component. The reason for the missing long component in KBr:Pb²⁺ and RbBr:Pb²⁺ is tentatively attributed to an anomaly in the structure of the adiabatic potential energy surface (APES) of the excited states.     

Electron-lattice interaction in the absorption spectra of thallium doped alkali halides

The electron-lattice interaction of NaCl:Tl⁺, KCl:Tl⁺, KBr:Tl⁺, and KI:Tl⁺ is discussed using the moments of the absorption bands. The discussion is based on a theory ofToyozawa andInoue andHonma. Consistency of the data is found for the absorption measurements. An analysis of the band shift under applied stress shows for theA-band in KCl and KBr and for theA- andB-band in KI that the electronlattice coupling constants derived from these data assuming next neighbour interaction differ considerably from those derived from the second moments of the bands.     

Optical absorption of s2-configuration ions in alkali halide crystals—III: The A band in Sn2+-doped crystals

The line shape of the A band in KCl:Sn²⁺, KBr:Sn²⁺, KI:Sn²⁺, RbCl:Sn²⁺ and RbBr:Sn²⁺ has been measured as a function of temperature between about 15 K and room temperature. As the spectra for all these systems are similar detailed results are presented only for RbCl: Sn²⁺, RbBr:Sn²⁺ and KBr: Sn²⁺. The experimental data resemble those of a previous study on KBr:In⁺ and KG:In⁺ in that the A band consists of two broad, overlapping components designated A₁ (the low energy component) and A₂. The separation between A₁ and A₂ is more marked at low temperature for Sn²⁺ than for In⁺, and no inversion of the ratio of the peak heights of A₁ and A₂ occurs as the temperature is varied, as was so for In⁺. Detailed calculations of the line shape are presented for KBr:Sn²⁺. These calculations show that one cannot account for the line shape purely in terms of the dynamical Jahn-Teller effect and that there is in addition a static splitting of the A state caused by a lowering in the symmetry of the crystal field.     

Absorptions- und Emissionsspektren einfach und mehrfach aktivierter Kaliumbromidphosphore

The absorption and emission spectra of Pb⁺⁺-, Tl⁺-, Ag⁺- und Cu⁺-activated potassium bromide crystals have been studied at room temperature. The absorption spectra of KBr-crystals, which are activated with combinations of these ions are additively combined of the absorption bands of the singleactivated crystals. The emission spectrum of KBr(Tl) is changed by the addition of the other activators in KBr(Tl). This fact demonstrates that the absorption and emission of light in KBr(Tl)-phosphors is caused by transitions between states of the KBr-lattice and states of the Tl⁺-activator. A corresponding model for these transitions in KBr(Tl) is suggested.     

The Hd-center interaction with a Rb+ ion during irradiation and thermal annealing in kBr

The role of Rb⁺ ions on defect formation in KBr has been studied. The impurity suppresses colorability due to X-raying at 6 K, but does not result in the formation of any centers characteristic to Rb⁺ ions at this temperature. A new optical absorption band peaked at 3.19 eV is produced only by thermal annealing of irradiated KBr:Rb. This band is annealed in parallel to the annealing of the F band in a stage at 55 K, obeying second-order rate equation with an activation energy of 0.102 eV. This band is ascribed to the H_A(Rb⁺)-center. Calculation is made on the elastic interaction energy between the H-center and a Rb⁺ ion, to show that the interaction along 〈110〉 is repulsive, whereas that along 〈001〉 is attractive. Based on this result of calculation, the structure and the formation mechanism of the H_A(Rb⁺) center, and origin of suppression of colorability at 6 K are discussed. The difference in the interaction of the interstitial atom with Rb⁺ during its dynamical motion and thermal motion is emphasized.     

Thermomodulated A-band absorption of KBr: Tl

A marked oscillator-strength decrease of the A band in KBr: Tl has been pointed out by means of thermally-modulated optical measurements throughout the temperature range 88–380°K. The experimental results suggest the existence of a clear correlation between the states responsible of the absorption bands and are discussed in order to clarify the role of the thermal perturbation upon Tl⁺ energy levels.     

Luminescence and relaxed excited state origin in CsI:Pb crystals

Emission and excitation spectra, luminescence polarization and decay kinetics have been studied for CsI:Pb crystals in the 0.36-300 K temperature range. The origin of the excited states responsible for the optical characteristics has been discussed. It has been concluded that the doublet ≈3.70 eV absorption (excitation) band is caused by the electronic transitions into the Pb²⁺ triplet state split due to the presence of a cation vacancy near a Pb²⁺ ion, while the higher-energy bands are of the charge-transfer origin. Like in CsI:Tl, four emission bands of CsI:Pb have been found to belong to the main luminescence centres. Two emission bands, peaking at 3.1 and 2.6 eV, are suggested to arise from the triplet relaxed excited state of a Pb²⁺ ion. Two visible emission bands, peaking at 2.58 and 2.23 eV, are interpreted as the luminescence of an exciton localized near the Pb²⁺ ion.     

利用偏振喇曼谱研究KBr:Pb2+单晶中的HD色心

本文报道掺铅溴化钾单晶在液氮温度下经大剂量X射线辐照后的偏振喇曼测量结果。利用几年前才发展起来的所谓“表现型”分析方法,确认喇曼谱中频移为186cm^-1的信号具有点群C_1k(010),它起因于H_D色心的A模振动。 关键词：     

Thermoluminescence and photoluminescence studies on gamma irradiated CsI: Pb2+ crystals

Pure and Pb²⁺-doped CsI crystals have been grown by the Bridgemann technique. Optical absorption, thermoluminescence (TL) and photoluminescence (PL) measurements have been performed. In undoped and Pb²⁺-doped cesium iodide crystals, F-centers and V-centers have been produced at 770 nm and 350 nm, respectively. In Pb²⁺-doped crystals, additional centers at 373 nm, 290 nm and 258 nm bands have been produced. In undoped samples, only two glow peaks at 343 K and 373 K have been produced, and in Pb²⁺-doped samples additional glow peaks at 383 K and 423 K have been produced. For all the samples, TL emission, PL and excitation measurements have been performed.     

The optical properties of thallium,lead and bismuth in oxide glasses

Absorption, fluorescence, excitation and decay time measurements have been made on a range of glasses containing thallium, lead and bismuth. In calcium phosphate and sodium silicate glasses the bands in both absorption and emission have been assigned to the A band of the Seitz model. For the bismuth doped glasses the A band was always observed in absorption but the emission was very dependent upon glass composition. Configurational coordinate curves have been constructed for Tl⁺ and Pb² in a glass of composition CaO. P₂O₅. Coordinate diagrams are also used to explain the presence or absence of bismuth fluorescence in certain glass compositions. In some borate glasses containing bismuth a brown colouration was observed. This was probably due to particle separation. No A band emission was observed from bismuth in a calcium phosphate glass. Instead there was a faint red emission similar to the cathodoluminescent bands of crystalline calcium phosphates.     

Effect of magnetic field on luminescence of MgS,CaS and CaO phosphors activated with Bi3+ ions

The magnetic field dependence of the intensity I(A₀) of the zero-phonon line of the ³A_1u → ¹A_1g emission band is measured at 4.2 K for MgS, CaS and CaO phosphors activated with Bi³⁺ ions. The increase in I(A₀) is proportional to the square of the external magnetic field. The results are compared with those for Pb²⁺-activated phosphors.     

Magnetic susceptibility study of Ce in PbCeA (A=Te,Se, S)

The magnetic susceptibility of Pb_1-xCe_xA (A=S, Se and Te) crystals with Ce³⁺ concentrations 0.006≤x≤0.036 was investigated in the temperature range from 2 K to 300 K. The magnetic susceptibility data was found to be consistent with a ²F_5/2 lowest manifold for Ce³⁺ ions with a crystal-field splitting Δ=E(Γ₈)−E(Γ₇) of about 340 K, 440 K and 540 K for Pb_1-xCe_xTe, Pb_1-xCe_xSe, and Pb_1-xCe_xS, respectively. For all the three compounds the doublet Γ₇ lies below the Γ₈ quadruplet which confirms the substitution of Pb²⁺ by Ce³⁺ ions in the host crystals. The observed values for the crystal-field splitting are in good agreement with the calculated ones based on the point-charge model. Moreover, the effective Landé factors were determined by X-band (∼9.5 GHz), electron paramagnetic measurements (EPR) to be g=1.333, 1.364, and 1.402 for Ce ions in PbA, A = S, Se and Te, respectively. The small difference with the predicted Landé factor g of 10/7 for the Γ₇ (J=5/2) ground state was attributed to crystal-field admixture.     

Photoluminescence, optical absorption and XRD studies on X-ray irradiated terbium doped KBr crystals

This paper reports the optical absorption, photoluminescence (PL), XRD, SEM studies made on KBr:Tb³⁺ crystals. The integrated light intensity is enhanced by about two orders of magnitude as compared to the undoped samples in spite of some OH^- present in the samples. PL of these crystals exhibits characteristic Tb³⁺ emissions due to transitions from the ⁵D₃ to ⁵D₄ levels to various levels of the ⁷F septet on F-bleaching X-ray irradiated crystals Z₃ centers are observed. The bands observed in the emission spectra of Tb³⁺ doped KBr are found to be shifted to higher wavelength. The stokes-shift of KBr:Tb³⁺ is determined and it is found to have a large value. The XRD studies have been made to determine the crystalline structure of KBr and KBr:Tb³⁺ and also the Miller indices. The SEM studies made reveal the presence of microcrystalline structure.     

Radiative energy transfer from Pb2+ to Eu2+ ions in NaCl,Kcl, and KBr single crystals

In the present work, the emission and excitation spectra of NaCl, KCl, and KBr doubly doped with europium and lead ions were investigated. In all cases, excitation with light lying in the A-band of the Pb²⁺ ions produces in addition to the ³P₁ → ³S_o Pb²⁺ emission, the 4f⁶ 5d (^t2g) → 4f⁷ europium emission. This fact indicates that energy transfer occurs from Pb²⁺ to Eu²⁺ ions. From the data obtained, it was determined that the energy transfer process is of a radiative nature and that it is more efficient in KCl than in either of NaCl or KBr. A possible explanation for this fact is given.     

Decay modes of the 3000 Å emission band in KCl: Tl+

The time behavior of the 3000 Å luminescence signals of KCl: Tl crystals is complex. Three different components can be resolved in the temperature range investigated (80–340K). These results that are typical for the A_x emission of phosphors like Kl:Tl⁺ and KCl:Pb²⁺, cannot be explained with the available theoretical models for KCl:Tl system.     

Low-temperature spin configurations in ErFeO3 and DyFeO3

Low temperature spin configurations in ErFeO₃ and DyFeO₃ have been studied by Mössbauer spectroscopy in single crystals. In ErFeO₃ our results indicate a reorientation G_z → G_zy of the Fe³⁺ moments below 4K, already found by neutron diffraction and NMR experiments. In DyFeO₃, it is shown that the Dy³⁺ moments order in the A_xG_y or G_xA_y configuration below 3K. This ordering triggers a G_y → G_xy reorientation of the Fe³⁺ moments.     

Transient optical absorption and luminescence in <Emphasis Type="Italic">A</Emphasis>Pb<Subscript>2</Subscript>Cl<Subscript>5</Subscript> (<Emphasis Type="Italic">A</Emphasis> = K,Rb) crystals

This paper reports on a study of transient optical absorption and pulsed cathodoluminescence in APb₂Cl₅ (A = K, Rb) in the visible and ultraviolet spectral regions. The measurements performed by absorption optical spectroscopy with nanosecond time resolution showed the transient optical absorption of APb₂Cl₅ to derive from optical transitions in hole centers, and that the optical density relaxation kinetics is mediated by interdefect tunneling recombination in complementary pairs which involves Frenkel defects on the cation sublattice and self-trapped carriers. The slow components in the transient optical absorption decay kinetics, with characteristic times ranging from a few ms to seconds, have been assigned to diffusion-mediated annihilation of interstitial atoms with alkali metal vacancies. The mechanisms underlying creation and relaxation of the short-lived Frenkel defects on the cation sublattice and self-trapped carriers have been analyzed.     

Anionische Silberzentren („B-Zentren“) in Alkalihalogeniden

It is proposed that negatively charged silver ions on anion sites are responsible for theB bands found in silver doped alkalihalides. Experimental investigations confirming this model of theB center are presented. Optical absorption and emission ofB centers were measured in seven alkalihalides in the temperature range from 450 to 4 °K. Configuration coordinate diagrams were obtained for KCl, KBr, and KI. A chemical method was used to determine the charge of theB center. Thermal or optical excitation causes theB centers to dissociate into neutral silver atoms andF centers. The Ag⁰ centers are bound to interstitial positions at low temperature. At high temperature they collect together forming colloidal centers. TetragonalB _A centers were formed during optical bleaching of theB band in mixed crystals of the type KCl+ΔNaCl. Their absorption and emission spectra, optical orientation, and polarized emission were investigated. These properties are shown to be similar to those ofF _A centers.B _A fluorescence polarized almost completely in the [100] direction was observed. A Jahn-Teller splitting of theB absorption band was resolved in RbCl at low temperature. The splitting confirms the configuration5s² for the Ag^? ion. The results are compared with those for the isoelectronic centers In⁺ and Sn⁺⁺. Thin films of alkalihalides containing small amounts of silver, copper, or thallium were condensed simultaneously with alkali vapor. New bands in the UV region were found, possibly due to Cu^? and Tl^? centers.     

Crystal and magnetic structure of KFeO2

The crystal and magnetic structures of KFeO₂ have been determined by neutron and X-ray powder-diffraction and Mössbauer-effect techniques. The crystal structure at 4.2 K and 300 K is orthorhombic and the magnetic space group is Pbca'. The Fe³⁺-ions in this structure are tetrahedrally coordinated by oxygen ions, and each Fe³⁺-ion has a magnetic moment which is antiferromagnetically coupled to the moments of four Fe³⁺-neighbours. The direction of the moments is parallel to the a-axis. A crystal phase transition has been observed near the Néel temperature?960 K.     

Optical absorption spectra of s2 impurity ions in aqueous halide ion glasses

The optical absorption bands of aqueous 0·05 M Sn²⁺ in 7 M LiI at 77°K appear at 361, 352, 325, 310, 300, 292 and 262 nm. They are considered to be the A₁, A₂, B, C₁, C₂, C₃ and D′ bands since the positions and relative intensities lie within the range of those bands for Sn²⁺-doped alkali iodide crystals. Upon warming the glass there is an uncorrelated increase in the B band and a decrease in the A₁ band. In 3·6, 4·1, 4·6 and 5·1 M CaCl₂ glasses with 5×10^?3 M Sn²⁺ the A₁ and A₂ bands show uncorrelated increases with increasing concentration of Cl^?. Comparable observations are reported for Pb²⁺-doped glasses of lithium halides and CaI₂. In general the spectra of the Sn²⁺- and Pb²⁺-doped glasses correlate well with those of the corresponding crystal systems. The effect of temperature and halide-ion concentration are attributed to shifts in chemical equilibria among the well-known halo complexes, MX_n^2?n MX_n?1^1?n+X^?, each having a characteristic, absorption and emission. Absorptions may be attributed to M²⁺(³P₁ ← ¹S₀) and M²⁺(¹P₁ ← ¹S₀) in the complex, shifted by partially covalent bonding of n halide ions.