Tunneling recombination luminescence in KBr and KCl

The tunneling recombination luminescence bands with maxima at 550 nm in KBr and 500 nm in KCl are due to electron tunneling transitions between the ground states of F and V_k centres. The emission of σ excitons occurs as a result of electron tunneling transitions from an electron centre (presumably an F' centre) to an excited state of the (V_k + electron) system. The KBr tunnel luminescence decay data are consistent with an isolated pair model, below critical X-ray excitation doses and at temperatures ranging from 100 to 150 K.     

On the nature of optically active centres in selfactivated luminophors of the CaWO4 type

The evidence in favour of the assumption that impurities of V group elements creates defects of the MeO′₄ type (centres of luminescence), Me?₃ and V_?, or WO₃ (capture centres) which are responsible for recombination afterglow different from the steady-state luminescence spectral distribution (Me = As, Sb, Nb, Ta; V₀ - oxygen vacancy) are presented. These same impurities, and phosphorous, lead to quenching of luminescence observed as afterglow with excitation quanta greater than 6.3 eV. This corresponds to the valued of the energy gap. Experimental data together with results of thermodynamic analysis lead to the conclusion that the luminescence of CaWO₄ and of other undoped oxygen containing compounds of transition elements luminophors is caused by direct self-activation connected with ability of these elements to convert spontaneously into a lower valency state and to form variable phases (non-stoichiometric compounds). It is proposed that in case of CaWO₄ centres of luminescence are formed by W⁵⁺.     

Luminescence in amorphous semiconductors

A review of the luminescence properties of amorphous semiconductors is presented. The materials covered are chalcogenide glasses, silicon and arsenic. Luminescence spectra, excitation spectra, temperature dependences and lifetimes are described.

The radiative transition in chalcogenides is the recombination of an electron in the conduction band tail and a trapped hole. A strong electron-phonon coupling distorts the lattice near the trapped hole, lowering its energy. This interaction is responsible for the broadness of the luminescence band and its position at about half the band gap energy. The recombination centre is thought to be a charged dangling bond with density 10¹⁷ cm^-3 in arsenic chalcogenides and 10¹⁶ cm^-3 in selenium. The same centre is observed in the hole drift mobility, and thermally stimulated conductivity.

Luminescence in amorphous silicon also originates from recombination between the band tails and deep centres, with three separate transitions identified. In contrast to chalcogenides the electron-phonon coupling is not strong. The shape and intensity of the spectra are very sensitive to sample preparation and treatment, and correlate with other electrical and optical properties of Si.     

An optically stimulated luminescence study of porcelain related to radiation dosimetry

This article describes the essential features regarding the photo-stimulated luminescence of porcelain: both the main ceramic and glazing materials are studied. In each case, radiation dose dependent signals are observed, superimposed on dose independent luminescence transitions that are both Stokes and anti-Stokes shifted in energy. Glazing is shown in some cases to be considerably more sensitive as a radiation dosemeter than the main porcelain ceramic. By comparison with the properties of artificial phosphors, the principal luminescent matrix is identified as being Al₂O₃, and the recombination centres in one glazing type are shown to be F-centres, Cr³⁺ and Dy³⁺.     

The effects of core structure on radiative and non-radiative recombinations at metal ion substituents in semiconductors and phosphors

Carrier binding and recombination processes at transition metal (TM) and post-transition metal impurities in solids are reviewed. The presence of low-lying empty core orbitals in these impurities introduces novel binding and recombination phenomena and leads naturally to a classification of impurity centres as ‘simple’ or ‘structured’. ‘Simple’ impurities, generally the main group elements, introduce only effective-mass-like states into the forbidden gap of the host lattice, whereas ‘structured’ impurities show localized atomic-like transitions below the lattice absorption edge. The fact that donor or acceptor centres generated by TM ions in semiconductors are usually deep is discussed with reference to a simple oxidationstate correlation diagram based on the variable chemical valency characteristic of these ions. Many metal ion impurities in solids generate iso-electronic centres however, and evidence is assembled to show how the normally accepted range of iso-electronic centres can be extended to include such impurities. It is emphasized that the formation of bound states at these ‘structured’ cationic iso-electronic centres is fairly common, in contrast to the situation normally found for anionic substituents in semiconductors. A possible explanation for this general property of structured iso-electronic centres is given in terms of the low-lying core levels which they may introduce in the band gap and their enhanced polarizability. Simple arguments then suggest that those centres showing electron ionization thresholds or atomic inter-configurational transitions just below E _g should be hole-attractive, whereas those showing charge transfer transitions should be electron-attractive. It is shown that two kinds of defect Auger recombination (DAR) may be significant for excitons localized at structured impurities. The first involves hole ionization at a deep neutral acceptor, and the conditions which must be met to make this process significant at room temperature are reviewed. The second DAR process involves the transfer of carrier recombination energy to the core electrons of the structured impurity. A simple model developed for this energy transfer process predicts that the coupling between exciton and core states will be larger if the impurity shows strong, broad dipole-allowed transitions quasi-resonant with the lattice absorption edge. Throughout the paper we stress the importance of recombination processes at structured impurities to the problems of phosphor activation and of shunt recombination mechanisms in semiconductor LEDs. In the final sections this general framework of ideas is used to explain the relative cathodoluminescence efficiencies of different rare-earth activators in crystals of Y₃Al₅O₁₂, with good agreement between the theoretical predictions and the experimental observations. Possible evidence for the occurrence of bound exciton states at structured TM impurities is found in the appearance of anomalously weak zero-phonon lines in the near-edge luminescence of GaP crystals prepared under special conditions.     

Thermal and non-radiative transitions of electrons at imperfections in ionic crystals

The theory of non-radiative and thermal transitions of electrons at imperfections in ionic crystals is elaborated. The results obtained are used to confirm Mott's and Gurney's theories on the detachment process in two steps of electrons from F centres during the absorption of light in the F band and to explain theoretically the temperature dependence of quantum efficiency. Good agreement with experiment was obtained. The possibility of the luminescence of alkali halide crystals containing F centres at sufficiently low temperatures was also determined.     

The decay of luminescence in natural and silver-doped quartz after X-ray excitation

It is well known that X-rays cause luminescence in quartz. This luminescence consists of two broad bands at 2.5 and 3.3 eV. After X-ray excitation natural quartz has an afterglow. The duration of this afterglow and the intensity of the emitted light show a strong dependence on the temperature of the sample. While the intensity is not so reproducible, the duration of the afterglow has a clear temperature- dependence and can be connected with two electron-traps in the customary band model — one with a depth of 8 meV and the other with 260 meV — using an Arrhenius-plot. If the quartz crystal has been doped with silver by electro-diffusion, additional luminescence bands at 2.2 eV and around 5 eV occurs. The latter broad luminescence band consists of a dominant part with a decay-time of 40 μsec at 4.8 eV and a weak band at 5.4 eV without afterglow. In contrast to natural quartz, the luminescence intensity as well as the decay-time in the silver-doped sample is independent of the temperature in the range 77–300 K. This constant afterglow is associated with partially forbidden transitions in the silver dopant and energy-transfer to the luminescence centres. In the suggested luminescence model, the observed luminescence bands are connected with an energy transition in the silver.     

Photoluminescence from gold centre in silicon

A sharp line structure attributable to ?honon assisted radiative emission has been observed in the low temperature photoluminescence spectra from deep centres in bulk samples of gold-doped silicon. The entire luminescence band which peaks near 0.78 eV is attributed to transitions of conduction electrons towards the gold-related donor level.     

Astronomical Spectroscopy: An Introduction to the Atomic and Molecular Physics of Astronomical Spectra, 2nd edn., by Jonathan Tennyson Atomic Astrophyiscs and Spectroscopy,by Anil K. Pradhan and Sultana N. Nahar

Much of our knowledge about magnetic centres in solids haa been obtained using magnetic resonance. The experiments rely upon detecting the absorption of microwave or radio frequency radiation by the centres at charaateristic values of an applied magnetic field. The method in its conventional form is usually restricted to the ground states of systems, since, even for long-lived excited states, there are at any instant insufficient numbers of excited centres to give detectable absorption signals. It is, nevertheless, possible to observe magnetic resonance in many of these excited states provided that optical methods of detection are used, since the magnetic resonance often affects some property of the luminescence, such aa intensity or polarization. The purpose of this article is to describe how optically-detected magnetic resonance experiments are carried out and to discuss the types of system to which they may be applied. It will be seen that, as well as providing details of excited states, the technique enables one to investigate the luminescence process itself.     

Cubic and tetragonal Ce ions in strontium fluoride

Optical absorption spectra in the vacuum ultraviolet, and high resolution emission and absorption spectra in the ultraviolet region of cubic and tetragonal Ce³⁺ centres in SrF₂ crystals were measured. Cubic centres are characterised by the zero phonon line at 33250 cm⁻¹ and a sharp phonon line is spaced from the zero phonon line by 410 cm⁻¹. The decay times of the luminescence from the cubic or tetragonal centres are equal to 32 ns. A comparison of the cubic and tetragonal spectra allows us to determine the influence of the charge compensating interstitial fluorine ion on the f and d levels of the Ce³⁺ ions.

Unrestricted Hartree–Fock calculations of Ce states in molecular clusters of alkaline-earth fluorides were performed. To make the calculated transitions coincide with the experimental one it is necessary to take into account the shift of the Ce³⁺ and interstitial F⁻ ions toward each other by 10% of initial distance.     

Luminescence spectroscopy of the earth

The first attempt to consider global radiation luminescence fields (spheres) of the Earth has been undertaken. In general four types of luminescent fields characterize the superficial geospheres. (1) Luminescence of organic and bioorganic substances comprising the atmosphere, the hydrosphere, the lithosphere and the technosphere, being a unique distinguishing property of our planet in the Universe. (2) Recombination luminescence of key rock-forming minerals (feldspar, quartz, carbonates) that is characteristic of the granite and sedimentary layers occupying some 30% of the Earth's crust. (3) Photoluminescence of dozens of ironless minerals in so-called fluorescence anomalies formed with the help of fluids ascending along fractures and faults to the surface of the Earth. While ascending they accumulate many rare metal elements including transition ones. Entering crystal lattices of ironless mineral-dielectrics these metals form centres of luminescence. (4) Artificial luminescent materials created in the technosphere in the 20th century. The main types have origins in natural luminophors. So, in every field of application of photo-, thermo, cathodo-, electro-, X-ray-luminophors and laser crystals they have many analogues among the luminescent minerals.     

Luminescence of BaBrI Crystals Doped with Ce3+ Ions

Physics of the Solid State - The optical properties of BaBrI crystals doped with cerium ions are studied. The possible types of cerium-containing luminescence centres are established. Using the...     

半导体物理效应及其应用讲座第四讲光吸收跃迁效应与半导体红外探测器的应用发展

光吸收跃迁效应是半导体光电探测器的基本物理过程.文章主要介绍光吸收跃迁效应在窄禁带半导体红外探测器应用方面的研究进展.讨论窄禁带半导体带间光吸收跃迁的理论和实验.文章还介绍了本征光吸收系数的表达式及其在材料表征和确定器件截止波长方面的应用,以及它在解释近年来发现的HgCdTe光电二极管电致负荧光现象方面的应用.     

Photoluminescence and luminescence excitation spectra in ZnSiP2

Summary Measurements of photoluminescence and luminescence excitation spectra of ZnSiP₂ have been performed at 4.2K and two results were obtained. One is the observation of a new sharp emission line at 1.980 eV, due to the bound exciton associated with the pseudodirect gap. The other is the observation of another new series of absorption lines in the luminescence excitation spectrum of an emission line, at 1.984 eV, in addition to those reported previously. These results indicate that in ZnSiP₂ radiative transitions occur at both the indirect and the pseudodirect gaps. Paper presented at the ?V International Conference on Ternary and Multinary Compound?, held in Cagliari, September 14–16, 1982.     

PbWO4闪烁晶体的发光动力学模型

在对PbWO₄闪烁晶体的光谱特性、发光衰减及其温度依赖以及热释光的研究基础上,并结合理论计算,提出了PbWO₄晶体发光的动力学模型,给出了PbWO₄晶体的基本能带结构及激子发光中心能态、陷阱能级在能隙中的位置。用此模型可以完整说明PbWO₄的发光过程,特别是导致室温下发光效率低的原因。最后还对其主发射成分蓝、绿发光中心的起源作了简要讨论。     

Recent developments in the optical spectroscopy of II–VI compound semiconductors

This review emphasises the information on the binding energies and the identities of electrically impurity and defect centres in II–VI semiconductors which may be obtained from optical spectra. Those shallow centres which may promote useful electrical conductivity are of particular interest. They contribute the richly structured near gap (edge) luminescence, containing weak to moderate phonon coupling and therefore very accessible information about the energy states of the different centres. It is shown that improved material and spectroscopic techniques have yielded considerable information about donors and, particularly shallow to moderately deep acceptors in ZnTe, a key II–VI semiconductor. Persistent impurities such as Li and Cu exert a greater influence on the properties of this semiconductor than formerly supposed. This influence is traced to other II–VI semiconductors, particularly ZnSe. Both the Cu_Zn and P_V acceptors appear to be much deeper in ZnSe than in ZnTe due to lattice relaxation, although evidence for a shallow P-related centre, probably a complex, is presented. Finally, some comments are made about the energy states of centres involving native defects in these compounds, particularly the V_Zn-donor associate centre, responsible for the self-activated luminescence.The author is grateful to D. Bensahel, R. N. Bhargava, S. G. Bishop, H. G. Grimmeiss, N. Magnea, J. E. Nicholls, J. Pautrat, D. J. Robbins, H. Tews and H. Venghaus for permission to use some of their data in this paper. He is also grateful to several of these and other colleagues. cited in the references for discussions of some of the problems described here.     

Photoluminescence and photostimulated luminescence in the X-ray storage phosphor BaBr2 doped with cerium

In orthorhombic BaBr₂ : Ce³⁺ two kinds of luminescence bands at room temperature have been attributed to charge-compensated Ce³⁺ centres. One type was associated with potassium (or some other monovalent cation) on a neighbouring Ba site and another one associated with an unidentified defect. A third kind of emission, observed only as low temperature photoluminescence (PL), is ascribed to isolated Ce³⁺ ions. The charge-compensated Ce³⁺ complexes are active both in PL and photostimulated luminescence (PSL) following X-ray irradiation. The PSL is nearly as efficient as in the case of the commercially used X-ray storage phosphor BaFBr:Eu²⁺. The X-ray induced electrons are trapped in F-type centres whose band position is characteristic for the nearby Ce complex. As shown by the fingerprint character of the PSL itself, the hole partner in the recombination is also associated or identical with the same Ce complex.     

GaN:Zn发光的显微观察

利用扫描电子显微镜(SEM)观察了气相外延GaN:Zn晶片的表面形貌、Zn浓度分布和阴极射线发光微区光谱及其MIS结构的电致发光微区光谱。研究表明,Zn杂质掺入GaN可以形成四种能量位置的发光中心;它们的形成与Zn浓度和晶体的微区结构有关;二者的不均匀决定了发光的不均匀性。     

Characterization of luminescence centres in neodymium implanted zinc sulphide

Analysis of the cathodoluminescence emission spectra of neodymium implanted cubic single crystal ZnS as a function of post-implantation annealing temperature has enabled groups of emission lines to be identified as originating from transitions within particular luminescence centres. For each group of lines the wavelength separations yield energy splittings characteristic of the crystal field at the luminescence centre. Comparison of these splittings with values calculated by crystal field theory on the basis of a point charge model, with due regard to possible sites of cubic symmetry in ZnS, has allowed two luminescence centres (A and B) to be identified.Centre A, which exists at low annealing temperatures, consists of a Nd³⁺ ion situated interstitially with 4 tetrahedrally disposed nearest neighbour S^2? ions. At higher annealing temperatures the emissions from centre A were found to decline giving way to those of centre B, which analysis shows to be a Nd³⁺ ion situated on a zinc substitutional site.     

Quenching by electric fields of the luminescence of As2Se3 single crystals

High electric fields reduce the luminescence of As₂Se₃ at 77 K and increase simultaneously the photoconductivity. Comparison of both effects points to excitons as the source for emission of light whereas free carriers contributing to photoconductance recombine non radiatively. The field affects free excitons and their thermalization but does not ionize excitons trapped in radiative centres. At low excitation energy, in the range of indirect transitions, the field quenching of luminescence obeys a Poole-Frenkel behaviour. Such interpretation yields an exciton binding energy of 50 meV. The quantum efficiency of luminescence decreases to higher photon energy. Part of this decrease is related to an increase of the photoconductivity.