bluuebunny/crossref_metadata_2025 huggingface dataset:
X-Ray Transferred Thermoluminescence (XTTL) in Quartz Crystals.
Authors: Halperin A. , Katz S.
Published: February 2023

The measurements in the present work were carried out on unswept synthetic electronic grade quartz crystals. Samples were cut out of a Y-grown bar into separate plates belonging to each of the different growth sectors of a Y-plate (namely, +X, -X, +Z, -Z). Each sample was about 2x8x11mm3 with the main faces perpendicular to the Y-direction. Crystals were normally X-rayed (55Kv, 18 ma) for a few minutes at about 10K. The glow curve obtained then on warming the crystal exhibited a variety of peaks and differed in the +X samples compared to the +Z ones.1 The XTTL was observed when the X-irradiated +X-growth sample was warmed up to about 220K, cooled down end X-irradiated again at 10K. During the warm-up after the re-irradiation the glow curve exhibited an extremely strong peak near 190K (at a heatinc rate of 10k per minute). The 190K peak did not appear in the Z-growth samples. A necessary condition for the appearance of the 190K peak was the pre-population of the traps associated with the regular thermoluminescence peaks appearing in the 200 - 300K temperature range.
Deformation Induced Thermoluminescence in NaCl:Ca(T).
Authors: Joshi R.V. , Dhake K.P. , Joshi T.R.
Published: February 2023

The polycrystalline specimens of NaCl:Ca (10−3 m.f.) obtained by recrystallization from aqueous solution followed by annealing and rapid quenching from 750°C, designated as NaCl:Ca(T), exhibited well defined glow peak at 147°C. This has been found useful in determining the dose of ionizing radiations in radiation applications1. The present paper includes the study of effect of mechanical deformation on the nature of glow curves of NaCl:Ca(T) material. About 5 x 103 Kg/cm2 uniform pressure is applied for preparing tablets of 0.1 cm thick and 1 cm diameter. TL glow curve reader used for recording the glow curves, after a test dose of 700 R, is described earlier1.
Point Defects in BaS:Cu Phosphors
Authors: Rao R.P. , Rao D.R.
Published: February 2023

The role of defects (intrinsic / extrinsic) is well known in the general understanding of different electronic processes involved in the various structure-sensitive properties. Impurities present as traces or doped intentionally in the luminescent materials (activators/or co-activators) may act as trapping or recombination centres depending on their nature. Conventational measurements on TL, TSC, dielectric constant (k′), conductivity (σac) and EPR are being used to obtain information on the trapping and recombination mechanisms related to such impurity centres
Polarized Luminescence from Divalent s2-ion/cation Vacancy Complexes in Potassium Halide Single Crystals
Authors: Scacco A. , Jacobs P. W. M. , Belliveau T. F. , Kang J.-G. , Simkin D. J.
Published: February 2023

Polarized emission has been used to establish the excited state symmetry of s2-ion doped alkali halide single crystals. The polarization from univalent s2-ions (Ga+, In+, Tl+) has been attributed to vibronic coupling (dynamical Jahn-Teller effect) causing a tetragonal distortion of the center1. Some authors have attributed the polarization from divalent s2-ions to the Jahn-Teller effect1, while others have attributed it to a center with lower than cubic symmetry due to the associated charge-compensating vacancy2. In this paper, we show that either of the above models can be valid for divalent ions, depending on the relative magnitudes of the spin-orbit (SO) and Jahn-Teller (JT) interactions.
Spin Mixing Processes of the Optically Pumped F Centers via the Study of Magnetic Circular Polarization of Luminescence
Authors: Ohkura H. , Muramatsu S. , Akiyama N. , Kawano K. , Mori Y.
Published: February 2023

The spin mixing processes of optically pumped F center are specified by the spin mixing parameters ε's which represent the probability for the spin to be flipped in the optical cycle. One of the main aim of this talk is to estimate the mixing parameter εrl in the non-radiative transition (NRT) process as a function of pumping photon energy Eph. The spin mixing is caused by the spin orbit interaction in the optical cycle.1) The mixing parameter in the unrelaxed excited state (URES) denoted as ε+ and ε− are dependent on the spin quantum number of ±(1/2) of the ground state.2) ε0=(1/2)(ε++ε−) and δε =(ε−−ε+) are used for convenience. Now, the spin-orbit interaction constant λ in the relaxed excited state (RES) was found to be small of less than one hundredth of λ value in the URES.3) The calculated mixing parameter in the RES was also found to be negligibly small.4) This evidence implies that, during the NRT process from the URES to the RES, the pumped F electron should pass down many sorts of multi-phonon levels characterized by λ values decreased gradually. Thus, the spin mixing parameter εrl cannot be neglected in the argument of the spin mixing processes in the cycle.
On the Nature of Gd3+ Luminescence Centers in the Crystals of the Alkaline Earth Fluorides
Authors: Orlov Ju. N. , Aleshin V.I. , Bozhevolnov V.E. , Ivanov L.N. , Karelin V.V. , Saparin G.V.
Published: February 2023

Unlike other rare-earth ions the ions of Gd3+ have intense luminescence in all solid solutions with fluorite structure as MF2-GdF3 where M is Ca, Sr, Ba [1]. The ESR, scanning electron microscopy, optical spectroscopy have been used for the study of MF2 – GdF3 structures which included GdF3 with concentration in the range of 0,001 - 40,000 %. As the results of experiments the three intervals of Gd3+ concentration were discovered in CaF2 - GdF3 system (below 1%, 1 - 15% and over 15%) characterized by different sets of Gd3+ luminescence centers. The peculiarities of the Gd3+ luminescence centers are: presence of cubic centers for all concentration intervals of impurity and high concentration of superfluous anion vacancies

F
v
−

in CaF2 - GdF3 and SrF2 - GdF3 systems. The latter stabilizes a complex claster of Gd3+ centers including also interstitial ions of fluorine Fi wich are prevalent type of Gd3+ luminescence centers for second and third concentration intervals.
Resonant Light Scattering and Hot Luminescence at the Indirect Gap in BiI3
Authors: Karasawa T. , Komatsu T. , Kaifu Y.
Published: February 2023

Layered BiI3 crystals exhibit allowed indirect exciton absorptions with unusually large transition probabilities assisted by LO-phonons. This makes us possible to observe clearly the secondary emission (SE) resonant to the exciton state.1) The SE spectra give deep informations on the dynamical relaxation processes of exciton. The spectra under resonance excitation by a tunable dye laser consist of one-phonon Raman lines, two- and multi-phonon resonant Raman lines (RRL) associated with hot-luminescence (HL) bands. The typical spectra observed in three samples are shown in Fig. 1. The RA+C line is the two-phonon RRL due to the zone edge LO-phonons A and C. As shown in Fig.2, the Raman intensity of RA+C shows resonant enhancement at the indirect edge

(

E

gx

i

+
A
(
Z
)

)

and changes sensitively depending on excitation energy ωℓ, lattice temperature and samples. The results can be interpreted by three kinds of damping processes; the sample dependent nonradiative decay σo, the scattering by LA- and LO-phonons which depends on temperature and ωℓ. These three parameters can be estimated quantitatively from the Raman intensity in Fig.2.2) The HL part LC due to recombination of the exciton assisted by the LO-phonon C has rather broad and structured lineshape reflecting directly the non-thermal equilibrium distribution which is constructed through the above three relaxation processes. The structures shift with ωℓ. The strong and relatively structureless LC band is observed in sample a (small σO), in which multiple LA-phonon scattering is dominant (Fig.1(a)). As going from sample a to b and c, since the nonradiative decay is getting to be significant, the HL band becomes weak, and the Raman-like structures coming from lower order LA-phonon scattering appear clearly (Fig.1(b) and (c)). These results give new informations on interpretation of the resonant Raman and hot-luminescence spectra observed in the secondary emission accompanied by phonons.
Collectively Desactivating Excited Configurations in Impurity Systems
Authors: Berezin Alexander A.
Published: February 2023

Consider a system of several spatially separated potential wells (trapping sites) in impure crystal or in a large molecule. Let few (but not all!) of these traps to be filled with electrons, which we call "outer" or "extra" electrons. As a practical realization of this situation one can think of a crystalline or a molecular complex with impurity centers in various charge states [1-3]. Consider, e.g., a 2-site impurity subsystem AB with an extra electron initially residing on site B. Due to the random fields of other crystalline defects the (filled) energy level of an electron on site B may be slightly raised relatively to the corresponding (vacant) level of the site A. As a result, the outer electron can make a spontaneous tunnel transition (TT) from the site B to the site A. An excess of energy can be emitted as either phonon(s) or a low energy photon (infrared or microwave). Therefore, the initial configuration of the impurity pair is, in fact, a configurationally excited state which can decay to a lower lying (ground) state configuration through the exponentially slow spontaneous TT B → A of an extra electron [2, 3].
Photocaloric reevaluation of the nonradiative relaxation of Cr3+ in crystalline and amorphous hosts.
Authors: Strauss E. , Seelert W.
Published: February 2023

We report on an investigation of the nonradiative relaxation of photoexcited Cr3+ employing photocaloric spectroscopy. It is shown, that this method supplements fluorescence lifetime and photoacoustic measurements1) to completely determine the branching into different relaxation channels.

In photocaloric experiments one measures quantitatively that part of the absorbed photon energy that is converted into heat. Precise heat measurements are performed using a caloric compensation scheme. Suitable tests proved that all energy-absorbed from a laser beam is detected to within ±2 %, in the range 5 mW to 200 mW. A higher sensitivity can be achieved with more sophisticated control circuitry.2)
Phonon-coherent States and Response of Molecules and Crystals to Short Time Processes
Authors: Terzi N.
Published: February 2023

The coherent (or quasiclassical or Glauber) quantum states give in author's opinion a very concise and physical way to describe transient vibrational dynamics of molecules and solids, either when these systems are excited (mainly by processes which are short on the vibrational time scale) or when they, afterwards, relax under the action of internal forces. At such length that it seems possible to say that matter is much more coherent than so far assumed.
Two-Photon Luminescence Spectroscopy of Hg2Cl2 Single Crystals
Authors: Pelant I. , Ambrož M. , Hála J. , Kohlová V. , Vacek K.
Published: February 2023

Single crystals of Hg2Cl2 are known to be highly birefringet optical material of technical importance for polarizing prisms and other optical components in the visible region. However, some fundamental physical properties of Hg2Cl2, such as its energy band structure, are not known up to now. Absorption spectrum in the vicinity of absorption edge (~3.9 eV) was measured recently /1/ showing a distinct structure, but unambiguous interpretation is difficult to be done due to the lack of any band structure calculation. Important complementary information can be obtained, however, from two-photon absorption experiments especially in systems possessing a center of inversion, what is the case of Hg2Cl2 crystals (D2h point group for T < 185 K, D4h for T > 185 K). Recently, we have reported for the first time observation of low-temperature two-photon absorption in Hg2Cl2 single crystals upon a pulsed dye-laser excitation and demonstrated the feasibility of its monitoring via a luminescence band at 396 nm (3.13 eV) /2/. In this contribution we wish to present and discuss two-photon exitation spectrum of the 396 nm emission band at T ~10 K in the region 4.16 ≤ 2hv ≤ 5.4 eV. The excitation spectrum is characterized by a gradual smooth increase starting from the low-energy side, a shoulder at 2hv ~4.8 eV and a dominating intense maximum at 2hv ~5.14 eV. Compared to the one-photon absorption spectrum /1/, one finds “alternating” maxima which are observed or in one-photon or two-photon experiments, but which are not common for the both cases. Conclusions are made on the symmetry of related Brillouin-zone points and wavefunctions.
Time-Resolved Photoluminescence in SrTiO3
Authors: Leonelli R. , Brebner J. L.
Published: February 2023

SrTiO3 is an insulator with a band gap of 3,27 eV which shows evidence of strong electron-phonon interaction. Its luminescence spectra exhibits a broad band in the visible, apparently intrinsic in nature (1). Its transport properties reveal the existence of deep traps for holes (2) and small polaron behaviour has been observed for electrons in the conduction band (3).
Mechanisms of Exciton Trapping in Oxides
Authors: Hayes W.
Published: February 2023

The localisation energy required for intrinsic self-trapping of excitons increases with increasing bandwidth and calculation suggests that oxides are marginal cases for self-trapping. We have used ODMR of recombination radiation of oxides to study exciton trapping mechanisms. Work carried out in the past has shown that in oxides such as YAG1 and YA1032 excitons are trapped near defect sites. More recently we have studied the well-known blue emission of quartz at 4K3. Our results show that part of this emission arises from a triplet state of a trapped exciton and we have determined the principal magnetic axes of the centre. Comparison with other work4 suggests that the exciton is trapped in an efficient intrinsic radiolytic process involving the transient production of an oxygen Frenkel pair. The fine-structure splitting of the triplet state is unusually large (D = 22.6 GHz), consistent with an oxygen molecular configuration involving an interstitial oxygen. The model for this centre requires the interstitial oxygen and vacancy to be close together and to recombine in the process of radiative decay.
Spontaneous and Stimulated Emission by Self-Trapped Excitons in Cadmium Iodide
Authors: Cingolani A. , Ferrara M. , Lugarà M.
Published: February 2023

The spontaneous and the stimulated emission of CdI2 have been studied in the temperature range from 10 to 200°K, under low and high intensity of excitation by means of a nitrogen laser (Imax= 10 MW/cm2, τ= 5 nsec), whose photon energy was 3.68 eV, i.e. larger than the energy gap of the ionic crystals of CdI2. Our samples showed a 4H-polytypism as confirmed by the spontaneous Raman spectroscopy measurements performed by means of a 500 mW Argon ion laser excitation. Our crystals appeared unintentionally doped with Pb++, as confirmed by the spontaneous emission spectra at T=20°K obtained under dye laser (h ν =3.25 eV) excitation in resonance with Pb levels. The absorption due to these impurity levels strongly appears even at RT in the photoacustic spectra we have carried out. The spontaneus emission spectra at low excitation show a worth e-volution with the sample temperature of the competitive broad bands in the near ultraviolet and visible optical regions. The line shape of these bands, extracted from the total spectrum generated from their superimposing, results to be gaussian. The energy scheme to assign the nature of these bands could be that of self-trapped excitons typical of ionic crystals like CdI2. At high intensity the spectrum consist only in a very broad band, whose halfwidth of about 100 nm is independent of the sample temperature. The emission comes out from the whole sample surface even if the excitation is localized in a small spot. The stimulated emission shows the same feature of the spontaneous spectra obtained under high excitation. On the contrary the optical gain spectra show several main peaks that at 80°K are localized at 2.81, 2.53, 2.37 and 2 eV respectively. These gain peaks are well consistent with the maxima of the deconvolved bands observed in spontaneous spectra under low excitation. The values of the optical gain coefficient are surprisingly high (g ≧104 cm−1) for all the peaks at 80°K whereas at temperatures either lower or higher than LNT the optical gain shows a sharp drop. The integrated external efficiency of the stimulated emission from CdI2 at 80°K excited by N2 laser results of about 0.1%. The very high value of the optical gain coefficient of CdI2 at 80°K can be explained by taking into account that the self-trapped excitons levels diagram looks like the typical four levels laser scheme. Anyway the population inversion threshold up to-day can be overcome only by means of high intensity optical pumping(1).
Self Trapping of Excitons at the Surface of Rare Gas Solids and its Manifestation in Luminescence and Desorption
Authors: Coletti F. , Debever J.M.
Published: February 2023

This paper presents the first results on a correlation between the luminescence of excitons self-trapped at the surface of solid argon and desorption. Recently, Jennison and Emin showed that localisation of electronic excitation at the surface of the crystal is an essential condition, and that especially self-trapping of excitons can lead to desorption of neutral atoms1. In the case of solid argon, self-trapping of excitons at the surface has been proved to exist2. It leads to characteristic luninescence bands which were also measured with electron excitation techniques3. Two of them exactly coincide with the 3P1 and 1P1 emission of isolated argon atoms and were not understood up to now. In the course of this work it turned out that they are emitted by desorbing neutral atoms.
Optical-Environment-Dependent Lifetimes and Radiation Patterns of Luminescent Centers in Very Thin Films
Authors: Fattinger Ch. , Lukosz W.
Published: February 2023

The emission from luminescent centers located in a thin film (O) of thickness dO≪λ (where λ is the emission wavelength) is optical-environment-dependent: The raditive lifetimes depend not only on the refractive index nO of the film but also on the indices n1 and n2 of the adjacent media n1 and n2. The angular distributions of the emitted light differ drastically from the well-known multipole radiation patterns. From these electro-dynamical effects informations about the emitting centers can be obtained (determination of quantum efficiencies, multipolarity assignments, orientation of the emission dipoles).1,2
Differential Equations for Delayed Fluorescence-Kinetics in Living Plants
Authors: Krause H. , Kretsch G. , Gerhardt V.
Published: February 2023

The decay of the long-living delayed fluorescence (DF) of plants seems to have a complicated kinetic (1). The decay-curves of chlorella algae as a function of temperature are given in Fig. 1. The kinetic also depends on the excitation-wavelength.
Extra-Weak Spontaneous Chemiluminescence of Human Blood Detected by Ultra-High Sensitive Photon Counting System Developed for Biomedical Applications
Authors: Inaba H. , Takyu C. , Yoda B. , Goto Y.
Published: February 2023

With the development of optical electronics and a variety of its applications, the challenge of measuring ultraweak intensities of light from various types of faint source which releases merely a small number of photons is of considerable interest and attractive. With this aim, the photon counting technique has been developed and is now customarily utilized to detect very weak light intensities less than about 10-12 W in the visible and near infrared regions in conjunction with the high-sensitive photomultiplier. As a fascinating and interesting application of this technique to photobiology and photochemistry, we have detected extremely weak bioluminescence1 and chemiluminescence2,3 from various biological and chemical systems, such as living tissues like tumors and organs, and enzymatic reactions, and also analyzed their exceedingly weak spectra using a specially designed spectral analyzer system4.
Site Selective High Resolution Laser Spectroscopy of Europium in Calcium Binding Proteins
Authors: Valentini Mark A. , Wright John C.
Published: February 2023

Lanthanide ions are generally known to possess narrow 4fn to 4fn transitions in both excitation and fluorescence that are sensitive to the coordination environment surrounding the ion. Selective excitation with a narrowband laser can spectrally discriminate one lanthanide ion environment from another based upon differences in the crystal fields associated with the unique lanthanide ion sites. This paper describes site selective laser spectroscopic experiments where europium ions have been coordinated to proteins in sites normally occuppied by calcium ions.
The Role of Nonequilibrium Relaxation Phonons in the Luminescence of Activated Crystals
Authors: Kaplyanskii A.A.
Published: February 2023

Optical excitation of activated crystals is usually accompanied by the creation of "relaxation" phonons in the lattice (the "Stokes losses"). At low temperatures when the equilibrium phonon occupancies are small the nonequilibrium phonons thus formed may affect markedly the processes involving excited impurity ions and their luminescence characteristics. Investigation of luminescence effects associated with the nonequilibrium phonons provides valuable information on the dynamic processes in the excited state, on the various mechanisms of phonon interaction with impurity ions, as well as on the characteristics of the phonons proper, primarily of the terahertz range acoustic phonons.
Suppression of the Free-to-Bound Luminescence by EL2
Authors: Ossau W.
Published: February 2023

High purity nominally undoped and Sn-doped liquid phase epitaxial layers irradiated with 2 MeV electrons have been characterized by low temperature photoluminescence measurements. Analysis of the line-shape and the peak shift of the free-to-bound transition in magnetic fields up to 10 T allows an unambiguous identification of the impurities involved /1/. Care was taken to use identical excitation conditions for the measurements of unirradiated and irradiated samples during the annealing stages.
High Resolution Spectroscopy of Ni2+ - and M-centers in Polytypic ZnS Crystals
Authors: Broser I. , Broser R. , Birkicht E. , Hoffmann A.
Published: February 2023

Investigations of polytypic crystals have the advantage to allow a comparison of optical transitions in a center, which is situated in different symmetric environments. Cubic ZnS crystals, containing around 10−8 cm−3 nickel atoms, exhibit in the spectral region of about 810 nm several very narrow absorption lines, which can be attributed to crystal field transitions between the 3T1(F) and the 3T1(P) term of Ni2+ ions.1) ZnS crystals (with stacking faults), consisting of a great number of polytypic regions, show besides the cubic lines additional structure. Unexpectedly, the linewidth is as narrow as in the crystallographic homogenious case.
Laser Spectroscopy Studies of Recombination at Isoelectronic Oxygen Centers in ZnTe:0*
Authors: Jones E. D. , Hjalmarson Haroid P. , Norris C. B.
Published: February 2023

Using pulsed laser techniques, we have performed high-resolution excitation spectroscopy experiments on the luminescence of the oxygen center in ZnTe. These experiments were initiated to investigate the conjecture that free excitions are directly captured at oxygen impurities(1). The luminescence measurements were made for laser wavelengths varying from the bound-exciton zero-phonon absorption line to well above the band gap of ZnTe. A typical luminescence spectrum obtained at 10k with the pump laser tuned to the one phonon absorption peak is shown in the accompanying figure. When the laser was tuned to the free-exciton band, we found that the oxygen luminescence was enhanced. This result confirms the earlier conjecture of free exciton capture.
Luminescence in Annealed Electron-Irradiated High-Purity GaAs
Authors: Liu P.L. , Schmieder G. , Ossau W.
Published: February 2023

The samples studied are non-intentional doped and iron-doped high-purity GaAs liquid phase epitaxial layers irradiated with 2 MeV-electrons at room temperature. After annealing at 550 °C a new line appears at 1.5015 eV. The spectral position does not shift with the excitation intensity. We observe a fast decrease of the integrated luminescence intensity with increasing sample temperature. This points out to a particle (electron) loosely bound to the complex. No change in the energy position is observed in this temperature range.
A Comparison Of Calculated Impurity Wavefunctions With GaP:N Luminescence
Authors: Snyder Paul G. , Myles Charles W. , Gundersen Martin A.
Published: February 2023

Luminescence spectra due to impurities in a semiconductor contain contributions from both direct and indirect electronic transitions. In the indirect transition, a momentum conserving phonon is emitted or absorbed simultaneously with the emission of a photon. Because such transitions occur in all parts of the B illouin zone where the impurity wavefunction is non-vanishing, much information about the wavefunction (in k-space) can, in principle, be obtained from the phonon sidebands of the luminescence spectrum. In this paper, we derive an expression for the luminescence intensity due to indirect transitions, as a function of energy, and relate it to the k-space charge density, |ψ(k)|2, of the impurity level. This expression can then be used to test the accuracy of particular theoretical models of localized wavefunctions and energy levels. A charge density in k-space is calculated by the use of a theoretical model, and the corresponding spectrum is then calculated according to our expression. We compare this with the measured luminescence spectrum, which has first been treated to remove configuration coordinate electron-phonon interactions.(1)
The 0.839 eV Cr-related luminescence center in GaAs:Cr
Authors: Fujiwara Y. , Kojima A. , Nishino T. , Hamakawa Y.
Published: February 2023

We have found that an arsenic vacancy contributes to the 0.839 eV Cr-related luminescence line in GaAs:Cr and the luminescence center is a complex involving a Cr at a Ga site and an arsenic vacancy in its nearest neighbor, based on systematic studies on high temperature thermal annealing of GaAs:Cr under excess arsenic pressure. This Cr-related deep center luminescence line was assigned as due to intra d-shell transitions in a Cr impurity in GaAs. Recent Zeeman data1) on this 0.839 eV line have shown that the luminescence center has <111> C3v axial symmetry rather than Td symmetry of an isolated Cr at the Ga site in GaAs crystal. This suggests that the contribution of another impurity or defect to the Cr-related center. The chemical identification of this partner of the Cr impurity in GaAs has not definitely been done, though the symmetry of the Cr-related center was confirmed by these Zeeman experiments. We have investigated this Cr-related deep center luminescence with samples prepared by different diffusion conditions of Cr into GaAs. As a result, we have found that the intensity of the 0.839 eV Cr-related luminescence line decreases with increasing the arsenic pressure in a sealed quartz ampoules for Cr diffusion in GaAs. Based on these results we have proposed that an arsenic vacancy is a probable candidate as the partner of the Cr in the complex.2,3)
Luminescence Excitation Mechanisms in CdS from Dependence of Photoluminescence and Thermoluminescence on Persistent Conductivity Stored Charge State
Authors: Reed M. A. , Honig A.
Published: February 2023

The details of the mechanisms for energizing donor-acceptor (D,A) pairs which result in recombination luminescence are still not completely understood. Recent work1 on CdS has indicated that polaritons generated directly or as a consequence of incident photon excitation processes play the principal role in the D+,A− to D°,A° charging process, and that the luminescence emanates from the near-surface (~1 μm) regions. Experiments we report here indicate that polaritons also generate the stored charge associated with persistent conductivity phenomena2 observed in high resistivity CdS. We show that generation of stored charge in the near-surface region (~1 μm), from which edge luminescence may be emitted1, is a precondition for polariton-energized edge emission actually to occur. This requirement, taken together with the results of more detailed studies of the correlation between persistent conductivity and edge luminescence, supports the reported restriction of edge emission to near-surface regions1 and also establishes the spatial extent of the stored charge region at saturation of persistent conductivity as a few hundred microns into the interior. It is further shown that the stored charge associated with persistent conductivity is the source of thermoluminescence, with the glow curves associated with the free-to-bound high energy series (HES) and with the bound-to-bound low energy series (LES) peaking respectively at temperatures of 22K and 27K for a 10K/min temperature scan rate. These results, as well as those from isothermal thermoluminescence experiments, establish a low activation energy electron localized state as the source of persistent conductivity stored charge. We have associated this state with a large-lattice-relaxation3 D− center, based on the luminescence as well as other experiments. Edge luminescence produced by thermal release of these charges, residing at known spatial location (depending on the accumulated fraction of saturated stored charge), complements time-resolved excitation spectroscopic photoluminescence experiments in elucidating the impurity pair charging mechanisms. Luminescence spectral response to near infrared stimulation as a function of stored charge state is also presented and discussed.
Computer Simulation of Energy Transfer: Application to the Photoluminescence in CdMnTe
Authors: Kett H. , Gebhardt W.
Published: February 2023

We report on a computer simulation of the radiationless energy transfer1) between Mn2+ -ions in Cd1−XMnXTe. The model was applied to explain the photoluminescence properties in this material and in other II-VI-semiconductors with high manganese concentration. An fcc-lattice with 4096 lattice points and periodic boundary conditions is randomly occupied with "active" ions corresponding to a molar concentration x. The active ions are given 2 electronic states with energies Eg and Ee = Eg+ EO + N ΔE, where N is the number of "active" neighbors. The expression for Ee simulates the random crystal field seen by one active ion. The simulation starts with the excitation of a random active lattice point x. After an internal time interval Δt the excitation either decays with a certain probability W by photon emission or is transfered to a random neighboring active lattice point x′. If it has to step up in energy, the transition probability is to exp

(

E
e

(
x
)
−

E
e

(
x
'
)
)

k
B

T

, if it steps down, the transition probability is one. This procedure is repeated until the excitation decays radiatively with energy E(x′) after n time intervals Δt. After 500 000 excitations the time resolved spectrum is determined from E(x′) and n, which is equivalent to the delay time in the time resolved luminescence experiment. The spectra depend on temperature and delay time.
Fluorescence Linewidths and Excitation Transfer in Eu0.2Tb0.8P5O14 Crystals
Authors: Laulicht I. , Meirman S. , Ehrenberg B.
Published: February 2023

Laser induced fluorescence spectra of Eu0.2Tb0.8P5O14+ crystals is studied at various temperatures in the 40-550°K range: a) Linewidth (steady state) experiments Fluorescence linewidth experiments show that the linewidths of the 5D0 → 7F1 triplet of Eu3+ change linearly with temperature in the 300-500°K range and do not demonstrate critical behaviour near the ferroelastic phase transition which is expected to occur at about 440 K in this crystal. Such a phase transition is accompanied by a strong reduction of the sound velocity, v, of some of the low

p
→

acoustic modes(1), and an enormous increase of the linewidths Δν is expected, at first sight, near Tc on account of Δν
α
v−5 dependence(2).
Energy Transfer Phenomena in Lanthanide Metaborates (LnB3O6)
Authors: Zhiran Hao , Blasse G.
Published: February 2023

The lanthanide metaborates LnB3O6 contain chains of composition

[

B
6

O

12

]

∞

6
−

which are linked together by the lanthanide ions. These ions are situated in a distorted ten-cornered polyhedron. These polyhedra, linked together by their common oxygen edges, form infinite layers (1). The shortest Ln-Ln distance is about 4 Å. Here we wish to report that these compounds are excellent host lattices for efficient luminescent materials.
Energy Transfer and Concentration Quenching for Cr3+ - and Yb3+ -doped Lithium Lanthanum Phosphate Glass
Authors: Miniscalco W.J.
Published: February 2023

The quantum yield of Cr3+ is low in all glasses for which it has been determined, but rare earth ions in glasses typically have high quantum yields. Thus, co-doping Cr3+ with a rare earth is an attractive approach to improving the overall efficiency of glass lasers and flat panel luminescent solar concentrators. To be effective, the Cr3+ → rare earth energy transfer must be rapid compared to the Cr3+ decay rate. We have investigated Cr3+ → Yb3+ energy transfer and concentration quenching for singly and doubly doped lithium lanthanum phosphate glass. This glass composition was chosen because it has been found to be a suitable host for increasing the overall efficiency of Nd3+ when co-doped with Cr3+.(1) Our results indicate that rapid Cr3+ →Yb3+ energy transfer occurs in this glass. However, for dopant levels at which energy transfer dominates the Cr3+ relaxation, significant Yb3+ concentration quenching is found.
The Energy Transfer in Multi-Component Plastic Scintillators
Authors: Huijun Yuan , Xiangtuo Wang , Yuying Ji , Yuanli Zhang
Published: February 2023

In the present work the energy transfer in four-dimensional poly-stryrene scintillators containing solute B-PBD, POPOP, Sg5 and RhB has been investigated. The scintillation procees in plastic scintillators containing primary and secondary solute has also been investigated by Birks (1.2). Here, more attention is point to the discussion of the energy transfer from secondary to fourth solute.
A Novel Mechanism for Energy Transfer between Rare Earth Ions
Authors: Strek W.
Published: February 2023

The theoretical understanding of resonant energy transfer between a pair of spatially localized lanthanide ions has been developed by Kushida [1]. His model was based on a simple application of Förster-Dexter theory [2,3] in which the transition rate of dipole-dipole energy transfer from the initial state | Dα Aβ > to the final state |Dα Aβ′> is proportional to the square of of modulus of where R is the separation between the donor - D and the acceptor - A ions.
Luminescence of Amorphous SixC1-x :H and Its Applications
Authors: Kukimoto Hiroshi
Published: February 2023

Hydrogenated amorphous silicon-carbon alloy(a-SixC1-x:H) prepared by glow-discharge deposition is a new luminescent material; the spectrum of photoluminescence and its decay time can be changed widely with composition.1,2) The emission mechanism is discussed based on the observations of the Stokes shift,2) decay time and polarization memory3) of luminescence.
Fluorescence Line Narrowing in Dilute Systems with Nearest-Neighbor Transfer
Authors: Huber D. L.
Published: February 2023

We outline the results of an analysis of fluorescence line narrowing1 in dilute systems. We assume that a fraction, p, of the sites on a d-dimensional lattice are occupied at random by optically active ions and that the transfer of optical excitation can only take place between ions occupying nearest-neighbor sites. The normalized intensity of the sharp line fluorescence following excitation of an inhomogeneously broadened line by a monochromatic source is equal to exp [−γRt], where γR is the radiative decay rate and  is the probability that an ion excited at t=0 is also excited at time t.2
Continuous-Time Random Walks and the Luminescence Decay in Disordered Systems
Authors: Blumen A. , Zumofen G.
Published: February 2023

Many dynamical problems in solid-state physics and chemistry are related to random-walks on periodic structures. In the last years processes of energy transfer and decay in disordered media have attracted considerable attention. One way to account for the disorder is the continuous-time random walk (CTRW), as used for electron migration in amorphous solids[1]. The standard CTRW involves a spatial regularization, in that the walk takes place on a periodic lattice and the disorder is mirrored in waiting-time distributions ψ (t)[2,3]. Another way to mimic the disorder consists in letting the walk take place on fractals, geometrical structures which are not translationally invariant but which display the dilatational symmetry of the percolative cluster[4,5]. For fixed waiting-times this procedure is complementary to the CTRW, in that the disorder is included in the spatial aspect.
Fluorescence and Lifetimes of Excited States of Pr3+ in LiLa1−xPrxP4O12 Crystals
Authors: Mazurak Z. , Łukowiak E. , Cywiński R. , Mugeński E. , Jeżowska-Trzebiatowska B. , Schultze D. , Waligora Ch.
Published: February 2023

The spectroscopic properties of praseodymium ions in inorganic matrices are certainly less investigated then other rare earth ions. This is mainly to difficulties which arrise in the interpretation of the experimental data. In our previous papers [1,2] the intensity analysis of f-f transitions of the Pr3+ ion in LiPrP4O12 as well as the crystallographic data, are presented. A laser action in this crystal was observed by Szafrahski et al. [3].
Electronic Structure of the Principal Uranium Centre in Sodium Fluoride
Authors: Runciman W.A. , Srinivasan B. , Saebo S.
Published: February 2023

It has long been known1 that uranium in sodium fluoride provides a complex fluorescence spectrum due to the presence of several centres. These centres are believed to be different uranium-oxygen complexes. The principal centres have C4v symmetry and have been attributed to UO5 groups2. Charge compensation is obtained if the hexavalent uranium ion substitutes for a sodium ion and the divalent oxygen ions substitute for five neighbouring fluorine ions. The fluorescence transition has a magnetic dipole character between non-degenerate states. Hence if the ground state has A1 symmetry the lowest excited state has A2 symmetry. The resonant fluorescent transition occurs at 563.6nm (17743cm−1). A theoretical model has been constructed along the lines of the calculations for the uranyl ion3. In this model excitation consists of an electron in a 2p oxygen ligand orbital being transferred to a uranium 5f orbital. There are a number of possibilities to consider as the electron may come from either the axial oxygen or the equatorial oxygens and in either case it can come from a σ orbital or a π orbital. Consider first the case of an electron coming from the axial oxygen ion. The determinantal wave functions for the excited states are of the form |σ f| or |π3 f|. The Hamiltonian includes one-electron, crystal field, spin-orbit, Coulomb and exchange terms. The ω - ω coupling scheme was used throughout the calculation. Matrices were constructed for the different representations of C4v symmetry. In the of model there are 3A1, 3A2, 4B2 and 7 pairs of E states. The spin-orbit coupling constant for the uranium 5f electron was taken to be 1950cm−1. Starting values for the exchange parameters were calculated from atomic basis functions using the computer program system MOLECULE. The crystal field, exchange and one-electron parameters were treated as variables. The matrices were diagonalized for different sets of parameters, and in the case of the E states g-values were calculated. Numerous calculations were made for different sets of parameters and a least squares fitting routine was used to get a fit between experimental and theoretical values of energy levels and g-values for the lowest seven excited states. It was not found possible to get a good fit on a σf model and the calculations were extended to the π3 f axial model and the equatorial model. For the equatorial model linear combinations of the various σ orbitals are formed to provide orbitals transforming as representations of C4v. A good fit has been obtained for the energy levels and g-values in the b2f model. This solution will be assessed critically for applicability to uranium centres in sodium fluoride.
Hyperfine properties of Tb3+: LaCl3
Authors: Pelletier-Allard N. , Pelletier R.
Published: February 2023

Lanthanum chloride is a good crystal host to get highly resolved optical spectra of substituted lanthanides, as some lines exhibit very narow widths (1,2,3). Therefore we have used it to study the dipolar magnetic and quadrupolar electric effects of Tb IV.
[Title not available]
Authors: Abbundi R. J. , Mathur V. K.
Published: February 2023

The effects of radiation on rare earth doped calcium fluoride have been the subject of a number of investigations in the past two decades. Merz and Pershan1,2 have shown that these materials undergo a charge conversion of RE3+→RE2+ when subjected to gamma or x-ray radiation at low temperature. The fluorescence spectra of Sm2+ in CaF2 has been examined using optical excitation3 and Sm3+ has been observed in x-irradiated CaF2.1,2
Cooperative Optical Transitions in CaF2:Yb3+
Authors: Zhang H. Y. , Brundage R. T. , Yen W. M.
Published: February 2023

It has been shown that Yb3+ ions in crystalline hosts can exhibit optical transitions involving pairs of ions, either two Yb3+ ions1 or Yb3+ paired with another rare earth, such as Gd3+, 2 or upconversion processes involving a number of Yb3+ ions.3 We have studied such transitions in CaF2:Yb using tunable laser spectroscopy.
Optically Stimulated Luminescence of MgS :Eu Phosphors
Authors: Rao R.P. , Gasiot J. , Fillard J.P.
Published: February 2023

The phenomena of optically stimulated luminescence (OSL) has been known since long time (1). Antonov-Romanovski (2) first suggested that IR sensitive phosphors like SrS :Eu,Sm for the dosimetry of ionising radiation. On these lines quite a number of publications appeared discussing OSL dosimetry over TL dosimetry (3) and also X-ray iamging. To understand the OSL phenomena, one needs excitation (UV), emission (visible) and stimulation (IR) spectra. OSL is identical to TL evaluation, which is also known as 'Cold Method' where stored energy in the material after excitation is obtained optically and thermally in case of thermoluminescence.
Cathodoluminescent Contrast of Direct Writing Patterns Made by the Scanning Electron Microscope
Authors: Saparin G.V. , Obyden S.K. , Chukichev M.V. , Popov S.I.
Published: February 2023

An increase of quantum yield under action of electron beam on the i-layer of GaN:Zn structure and KMgF3 crystals have been observed(1,2). By means of the SEM we have been studied the plastic scintillators, CdS, ZnO and GaN:Zn-layers on the sapphire. Long time kinetic of the CL for all above materials was taken by the SEM “Stereoscan MK IIA” equipped by luminescent attachments. The CL contrast of direct writing patterns made by e-beam in the SEM was also analized. The fig.1 shows normalized depen­dences of CL intensity on the e-beam irradiation time under room temperature. The CL kinetic for plastic scintillators and CdS are described by curve 1. A possible mechanism of CL decreasing is a degradation of materials under local temperature action and defects creation that increases the concentration of nonradiative centers. A CL intensity variation for ZnO crystal did not observed(curve2). The curve 3 shows GaN:Zn -kinetic function for CL. The evolution of the CL was studied when an e-beam is fixed on a point of specimen. The increase of quantum yield and a very long life time of nonequilibrium state induced by e-beam are specific for last material. Such peculiarity allows by the SEM in CL mode to separate activated and nonactivated regions with contrast factor in the range of 30-100%. Above noted phenomena as result of e-beam action on media are non reversible and therefore the CL patterns by means of the SEM are available. Comparing the contrast(K) for three above cases one can seen that K= (Iir-Inir)/Inir ≶ 0 (fig.2a,b), where Iir is CL intensity of irradiated areas previousely, Inir is CL intensity of nonirradiated areas previousely. The patterns on the plastic scintillators and CdS look like dark lines (K< 0) on the light field (fig.2a). The contrast patterns on ZnO crystals is absent (K=0). In this case the e-beam action effect is reversible with relaxation time smaller than 10−6s. For GaN:Zn layer K>0 (fig. 2b) and when Iir attains a maximum the K-value can reach the factor of loo. Besides the previousely irradiation areas of GaN:Zn-layer having Iir ≫ Inir keep the contrast under room temperature up to date more 24 month(for T=0–10°C over 10 year). Minimum sizes of luminescent patterns elements (lines, spots) are equal to 0,5-0,6 mkm. Patterns do not change own geometry in time. The limit of spatial resolution is determined by the volume occupied by scattered electrons of the primary beam. The direct writing and reading information by e-beam are available with digital and analogue modes. Writing density is over 108 bit/cm2. No change in the luminescent spectrum of GaN:Zn before and after e-beam action on layers was detected. The CL intensity is only varied. We suggest that the luminescence changes vs the irradiation time are due to possible generation of new radiative recombination centers in the volume.
Study of the Ambipolar Carrier Drift in Silicon by an Optical Time-of-Flight Method
Authors: Laurich B. , Forchel A. , Hoai T.X.
Published: February 2023

We present a new method to study the ambipolar expansion of surface excited plasma in Si, based on the time resolved detection of the luminescence of a doped layer opposed to the excitation area.

This novel time-of-flight technique is used to study directly the carrier transport below and above the critical temperature Tc=23K for electron-hole droplet (EHD) condensation. Previously studies of the movement of the EHD in Si have been limited by the lack of time resolution1. The same holds for the surface created plasma (EHP) above Tc for which a drift has been deduced indirectly by a line shape analysis of the EHP emission spectra2.
Airborne Detection of Materials Stimulated to Luminesce by the Sun
Authors: Hemphill William R. , Theisen Arnold F.
Published: February 2023

The Fraunhofer line discriminator (FLD) is an airborne electro-optical instrument which permits daylight detection of materials on the Earth's surface which have been stimulated to luminesce by solar ultraviolet and visible light. This instrument uses glass spacer Fabry-Perot filters of narrow bandwidth (<0.1 nm) to isolate a Fraunhofer line of interest (Hemphill and others, 1983). To measure the luminescence of a material, the FLD computes from reflected light the ratio of the central intensity of a Fraunhofer line to the solar continuum a few tenths of a nanometer distant; it then compares this ratio with a conjugate measurement in skylight and direct sunlight. Luminescence is indicated where the ratio measured from the target material exceeds the ratio measured from skylight and direct sunlight.
Systematic analysis of phosphor degradation under cathode-ray excitation.
Authors: Klaassen D.B.M. , de Leeuw D.M. , Welker T.
Published: February 2023

The external radiant efficiency of phosphors generally decreases under prolonged cathode-ray (CR) excitation. This so-called degradation effect is of great technological importance because it limits the lifetime of CR displays. The deterioration mostly increases with increasing excitation density. Thus, for applications at high density, such as projection television tubes, degradation is expected to be a major selection criterion for the phosphor.