Luminescence In KCl Research Articles

Study on Luminescence of KCl:Eu2+ Crystals after X-ray Irradiation at Room Temperature

Bleaching with the F-light at the excitation bandpass of 20 nm results in the phenomenon that F-centre peak and thermoluminescence (TL) glow peaks due to Fz- and F-centres identically decrease with the F-bleach time, whereas TL glow peak due to Fz-centre only remains almost constant irrespective of its time in the case of that at the excitation bandpass of 5 nm. Analysing the data on bleaching effects, absorption spectrum of X-ray irradiated KCl:Eu2+ crystal has a peak due to Fz-centre approximately within 20 nm of the wavelength 560 nm at F-centre peak. Electrons released from Fz-centres at 370 K and from F-centres at 450 K combine with Eu3+ ions, leading to the excited Eu2+ ions from which the luminescence at 420 nm is emitted.

The deformation stimulated luminescence in KCl, KBr and KI crystals

Currently, strengthening of the intensity of luminescence in alkali halide crystals (AHC) at lattice symmetry lowering is discussed as a promising direction for the development of scintillation detectors [1-3]. In this regard, for the study of anion excitons and radiation defects in the AHC anion sublattice at deformation, the crystals with the same sizes of cations and different sizes of anions were chosen. In the X-ray spectra of KCl at 10 K, the luminescence at 3.88 eV; 3.05 eV and 2.3 eV is clearly visible. The luminescence at 3.05 eV corresponds to the tunneling recharge [F*, H]. Luminescence at 3.88 eV is quenched in the region of thermal destruction of F′-centers and characterizes tunneling recharge of F′, VK-centers. In KCl at 90 K, the luminescence of self-trapped excitons (STE) is completely absent. In KBr at deformation not only STE luminescence, but also deformation stimulated luminescence at 3.58 eV were recorded, the last one corresponds to tunneling recharge of F′, VK-centers. In KI crystal at 10 K and 90 K at deformation, only STE luminescence is enhanced. There are no deformation luminescence bands in KI compares with KBr and KCl crystals.

Temperature dependence of the photostimulated luminescence in KCl:Eu2+

The goal of this work is to understand the physical mechanism behind the signal stabilization process in KCl:Eu2+, a storage phosphor material that has generated renewed interest due to its potential in radiation therapy dosimetry application. The temperature dependency of the photostimulated luminescence (PSL) spectra and intensity vs. time post X-ray irradiation was measured. Commercial BaFBr:Eu2+ materials were included in this study for comparison. Unlike BaFBr:Eu2+, broadening of the F(Cl−) stimulation band and red-shift of the peak were observed for KCl:Eu2+ with increasing temperature. For irradiations at temperatures lower than 200K, PSL intensity of KCl:Eu2+ showed recuperation behavior in the first 2h post-irradiation and stayed almost constant with time thereafter. Moreover, spatially-correlated storage centers increased from 24% for irradiation at 50K to 31% at 195K and almost 100% at room temperature. The data suggest that certain types of charge storage-centers were mobile and contribute to the fast fading in PSL.

Luminescence in KCl:Eu2+, Tl+ X-ray storage phosphors

Abstract KCl:Eu 2+ powder phosphors co-doped with thallium display an emission band around 300 nm with a weak shoulder around 380 nm attributable to centres involving Tl + ions in addition to characteristic Eu 2+ emission around 420 nm. An enhancement observed in the intensity of 420 nm emission with the addition of TlBr in KCl:Eu 2+ phosphors is attributed to the increase in the concentration of Eu 2+ ions in the phosphors as well as energy transfer from Tl + → Eu 2+ ions.

Spectral holes and induced luminescence in KCl co-doped withEu2+ and Eu3+ ions

The luminescence spectrum of KCl co-doped with divalent and trivalent europiumions was measured as a function of temperature in order to characterize novelspectral holes that appear in the blue emission from Eu2+. Theradiative energy transfer from Eu2+ to Eu3+ produces thespectral holes and induces the luminescence from Eu3+ responsiblefor the 5D0→7FJ (J = 0, 1, 2, 3, 4) transitions. Theholes and the induced luminescence are strongly associated with the thermalband broadening of the blue emission. In addition, the observed line splittingof the induced luminescence of Eu3+ is also discussed in terms of acrystal-field Hamiltonian.

Formation of S 2− and Se 2− molecular ions through photochemical reactions and their vibronic luminescence in KCl : MnS/Se crystals

It is found that when quenched KCl : MnS/Se crystals are irradiated with UV light, S 2 − and Se 2 − molecular ions are formed. By this method these molecular ions were effectively introduced into KCl lattice for the first time. At 8.8 K, such luminescence spectra consist of one or more vibronic series of zero-phonon lines associated with isotope structure and phonon-side bands. The spectroscopic constants ν 00, ω 0″ and ω 0″ x 0″ were calculated for the ground state of Se 2 − ions. On the other hand, from the detailed observation of photochemical reactions in KCl : MnS, it was found that Mn +, Mn 0 and F centers were produced following the formation of S 2 −. From above results, a model for the formation of S 2 − was proposed.

Optically stimulated luminescence in KCl:Cu x-irradiated at room temperature

Optically stimulated luminescence (OSL) has been observed in single crystals of KCl:Cu x-irradiated at room temperature. It is shown that electrons are liberated from anion sites during the OSL process. The OSL predominantly involves emission due to radiative transition (d↔s) of monovalent copper ions present in the lattice. The OSL emission shows a strong temperature dependence indicating a thermally assisted process. Electron-hole recombination followed by energy transfer to the Cu activator is suggested as a possible OSL mechanism in KCl:Cu. Preliminary results of OSL in KBr:Cu are also presented.

Time-resolved spectroscopy of the Eu2+ luminescence in KCl:Ba2+, Eu2+ KCl:Sr2+, Eu2+ and KBr:Sr2+, Eu2+

Fluorescence kinetic studies of the Eu2+ luminescence in freshly quenched crystals of KCl:Ba2+, Eu2+, KCl:Sr2+, Eu2+ and KBr:Sr2+, Eu2+ are reported. The measurements were carried out at 300 K, at low concentrations of the dopants, and after the crystals were subjected to severe quenching treatments. The results obtained suggested that small complexes of Ba2+-Eu2+ are preferentially formed in the lattice of potassium chloride. At variance with this situation, evidence for the preferential formation of Sr2+-Eu2+ close pairs was not found in the doubly doped crystals of KCl:Sr, Eu and KBr:Sr, Eu. These results are in good agreement with the ionic radius criterion proposed by Rubio and co-workers (1985, 1987, 1988, 1989) to predict pairing between two impurity ions in a solid material.

Luminescence of KCl:Bi3+ excited at the X absorption band

The emission from KCl:Bi3+ excited in the X absorption band (i.e. between the A and B absorption bands) was measured as a function of temperature. The polarized emission spectrum and the angular dependence of polarization ratio were also investigated. The X-band excitation produces two emission bands peaking at 345 and 395 nm, the centres of which are not the same. The loosely bonded Cl- ion arising from the substitution of Bi3+ ions into the KCl lattice is assumed to be the colour centre for the X-band emission. The definitive assignment of the two emission bands is presented in terms of the relaxed excited states of the perturbed Cl- ion, in which the Jahn-Teller interaction coupling to the B1 and B2 vibronic modes is taken into account.

Colour centres and luminescence in KCl:Ni crystals

AbstractOptical absorption, thermoluminescence (TL), and monochromatic thermoluminescence (MTL) glow curves, TL and X‐ray luminescence spectra of KCl:Ni crystal are measured. Strong absorption bands appear at 218 and 275 nm due to the transition of an electron from adjacent Cl− ion to Ni++ ion. The reduction of these bands upon X‐irradiation shows the trapping of electrons by the divalent impurity ions. Only the first peak at 90 °C appears in the TL and MTL glow curve. F bleaching neither produces Z centres nor reduces the V band appreciably but decreases the TL glow curve heavily. These results are also interpreted in terms of electron trapping by impurity ions. Emissions due to decay of STE (Cl ion trapping an electron in the excited state) near free cation vacancy (445 nm) or unperturbed lattice sites (545 nm) are very weak while those near Ni++ ions, free (585 nm) or associated with cation vacancies (380 nm), are very strong. This is due to the high mobility of STE and Cl centres towards Ni++ ions.

Effect of Magnetic Field on the Decay Kinetics and Polarization of the AT Emission of KCl:Ga at 0.38 K

AbstractThe AT luminescence of KCl: Ga is investigated at 0.38 to 100 K by spectral, kinetic, and polarization methods. At extremely low temperatures the luminescence decay curve in the magnetic field is decomposed into three components (fast, quick, and slow) with decay times dependent, but light sums independent of the field strength. Polarization degrees of the components are independent both of field and time. The experimental results are discussed in terms of a model suggesting a strong interaction of the optical electron of Ga+ with tetragonal vibrations of the crystal lattice.

Isothermal decay of luminescence and photostimulated decay of luminescence in KCl and KCl:Sn single crystals

Thermoluminescence (TL), isothermal decay of luminescence (IDL), and photostimulated decay of luminescence (PSDL) are studied in the case of single crystals of KCl and KCl:Sn. For KCl:Sn the normal TL measurements show four glow peaks at 63, 85, 124, and 167 °C while two peaks at 105 and 165 °C are obtained in the case of pur KCl. The IDLs of KCl:Sn at 75, 151, 180 °C and that of KCl at 190 °C are found to be monomolecular, while that of KCl:Sn at 130 °C and of KCl at 125 °C obeys a power law type of decay. The PSDL of KCl:Sn at 151 °C is again monomolecular whereas the PSDLs of KCl:Sn at 25 and 70 °C and of KCl at 25 °C are power law type. A tentative expanation for both the types of decay are given. Finally, from the measurement of photostimulated thermoluminescence (PSTL) it is concluded that at least a part of the traps is filled by electrons from F-centres through conduction band. Thermolumineszenz, isothermisches Abklingen der Lumineszenz (IDL) und photostimuliertes Abklingen der Lumineszenz (PSDL) werden für KCl- und KCl:Sn-Einkristalle untersucht. Für KCl:Sn zeigen die üblichen TL-Messungen vier Glowmaxima bei 63, 85, 124 und 167 °C, während zwei Maxima bei 105 und 165 °C im Fall von reinem KCl erhalten werden. Die IDL von KCl:Sn bei 75, 151, 180 °C und die von KCl bei 190 °C sind monomolekular, während die von KCl:Sn bei 130 °C und von KCl bei 125 °C ein Abklingen nach einem Potenzgesetz befolgen. Die PSDL von KCl:Sn bei 151 °C ist ebenfalls monomolekular, während die PSDL von KCl:Sn bei 25 und 70 °C und von KCl bei 25 °C durch Potenzgesetze bestimmt sind. Eine vorläfige Erklärung für beide Arten des Abklingens wird angegeben. Aus den Messungen der photostimulierten Thermolumineszenz (PSTL) wird geschlossen, daß wenigstens ein Teil der Haftstellen durch Elektronen aus F-Zentren über das Leitungsband gefüllt wird.

Deformation luminescence in KCl irradiated at room temperature

It has been found that there is a relationship between the thermoluminescence and the deformation luminescence of irradiated pure KCl samples. It is concluded that the luminescent process in the deformation luminescence is the recombination of interstitial halogen atoms with vacancy centres ( F, M) as well as in the thermoluminescence.

Laser stimulated luminescence in KCl and NaF containing color centers

A broad luminescence band was found in laser irradiated KCl and NaF crystal containing color centers. This emission extends on both sides of the laser line and is interpreted as “hot” fluorescence due to radiative retrapping of laser ionized color centers.

Studies of self-trapped exciton luminescence in KCl

Measurements have been made of the luminescence intensity, lifetime, emission spectra, and linear polarization of self-trapped exciton luminescence in KCl (2.31 eV) at temperatures of ${7}^{\mathrm{o}}$K and above. Data are interpreted in terms of an exciton energy-level structure composed of a singlet state approximately 15 meV above a triplet state. The singlet state is populated only by thermal excitation from the triplet. The observed polarization data are consistent with a reorientation of the self-trapped exciton in a state higher than those responsible for the characteristic 2.31-eV luminescence.

Luminescence of KCl:SbCl3 under ultraviolet excitation at liquid air temperature

Luminescence of KCl:SbCl3 under ultraviolet excitation at liquid air temperature

Temperature dependence of the decay time and quantum efficiency of F-center luminescence in KCl

Improved measurements of τ and η in the range 4.2–170°K reveal a temperature dependence of the radiative lifetime, τ R = τ η , consistent with recent Stark effect measurements.

The M-Center Luminescence in KCl and KBr Crystals

The M -center luminescence in KCl and KBr crystals has been investigated extensively over a temperature range from about 4°K to 370°K. From the temperature dependence of the band width of the luminescence, vibrational frequencies influencing the M center in the excited states are estimated as 3.9×10 12 cps and 3.8×10 12 cps, respectively, in KCl and KBr crystals. By stimulating the crystal with M 4 light almost the same luminescence as that by M 1 light is observed in KCl. New absorption bands, M L , being associated with the M center and located at 360 mµ, 308 mµ, 250 mµ, and 400 mµ, 325 mµ, 275 mµ in KCl and KBr crystals, respectively, have been found, which may be analogous to the L bands of the F center. By comparing with the quantum yield of the F -center luminescence, the quantum yield of the M -center luminescence is estimated as 0.37±0.05 in KCl crystals at liquid nitrogen temperature. From the temperature dependence of the M -center luminescence intensity the energy gap between the first excited ...

Polarization of F‐Center Luminescence in KCl due to Electric Fields

Polarization of F‐Center Luminescence in KCl due to Electric Fields

On the Kinetics of the Luminescence in KCl: Tl, KBr: Tl, and KI: Tl

AbstractThere are two theories on the kinetics of luminescence in KCl: Tl, KBr: Tl and KI: Tl, which are given in the papers [4 to 6] and [7 to 9]. In the present paper these theories are compared with known experimental results and this is found to lend support to the works [7 to 9].