Radiative recombination of donor-acceptor pairs in ZnTe

Lifetime of the first excited state of donor-acceptor pairs has been measured in ZnTe as a function of the donor-acceptor distance. The measured lifetime for the radiative recombinations of donor-acceptor pairs agrees well with the calculated one in which the central cell correction for the 1s state of the acceptors is taken into account. It has been found that the lifetime depends on the impurity concentration. The concentration dependence is discussed in connection with the non-exponential decay of the luminescence observed for more distant donor-acceptor pairs.     

The recharge-enhanced transformations of donor-acceptor pairs and clusters in CdS

Four types of different center transformation processes enhanced by photoexcitation are given consideration. (1) Association of shallow donors with one another. (2) Dissociation of donor-acceptor pairs (DAP). (3) Donor migration from dislocations into the bulk of the crystal and association with acceptors. (4) Dissociation of complexes, consisting of several DAP and deep acceptors. It is shown that processes 1 and 4 are due to the recharge of defects under illumination and their further diffusion, whereas in processes 2 and 3 so-called “phonon kick” may take place together with recharge.     

Application of indium nanowires to donor-acceptor pair luminescence

A novel, self-supported nanostructured powder electroluminescence (EL) device, consisting of a dilute layer of conductive nanowires, which directly contacts a ZnS phosphor layer and functions as rear electrodes, is reported in this paper. Indium nanowires fabricated by using a porous alumina template and hydraulic pressure injection technique induce a localized field in the phosphor that is much higher than the average applied field and hence excite the phosphor to luminesce. The mechanism for light generation from the nanostructured contact EL device can be understood from the bipolar field-emission model.     

Excitation spectra of donor-acceptor pair photoluminescence in ZnTe

Photoluminescence excitation spectra of donor-acceptor pairs have been observed in phosphorus doped ZnTe. Binding energies of the donor and the acceptor is estimated from the spectra. Emission spectra measured under below-band-gap excitation showed sharp bands superimposed with a broad emission band. The result indicates the existence of two decay processes under the below-band-gap excitation: (1) recombination of an electron and a hole trapped on a given D-A pair, and (2) recombination of D-A pairs with various distances for which bound electrons are formed via conduction band.     

Luminescence decay of distant donor-acceptor pairs in phosphorous-doped ZnTe

Luminescence decay of isolated donor-acceptor pairs has been measured over the range of pair distance R ～ 180 Å in phosphorous-doped ZnTe. Analysis of the recombination rate as a function of the pair distance suggests an asymptotic behaviour of the acceptor envelope function of the type exp(-r/a_A), with $\text{a}{}_{\mathrm{A}}\text{= 40 ± 10}\text{A}\text{?}$. This effective Bohr radius would correspond to an hydrogenic mass $\text{m}{}^1\text{= (0.13 ± 0.03)}\text{m}{}_{\mathrm{o}}$, which is close to the light hole mass as measured from cyclotron resonance experiments, $\text{m}{}^1\text{= (0.154 ± 0.005)}\text{m}{}_{\mathrm{o}}$. A discussion on the validity of the isolated donor-acceptor pair model is also given.     

The kinetics of donor-acceptor pair transitions with strong phonon coupling in GaP

Donor-acceptor pair luminescence in GaP was studied by time-resolved spectroscopy, by measuring and analysing the integral band decay over many decades of intensity and time and by measuring and analysing the temperature dependence of the luminescence intensity. We report here the results obtained with some or all of these techniques for pairs involving deep as well as shallow centres. Those with a deep centre are: S_P-Si_P and Si_Ga-Si_P, in which the acceptor is the deep centre, and O_P-C_P and O_P-Zn_Ga, in which the donor is the deep centre. These pairs all have a broad, phonon-dominated luminescence band. The pairs involving shallow centres include Si_Ga-C_P, S_P-C_P and Te_P-C_P. Due to the different way of momentum conservation in these pairs, those involving a donor on a Ga-site have strong phonon co-operation and weak zero-phonon (ZP) transitions, whereas those with a donor on a P-site have strong ZP transitions.With time-resolved spectroscopy, well-resolved structure, due to a ZP pair band and its phonon replicas, is obtained for nearly all pairs. A comparison is made with the structure obtained by measuring in the stationary state at very low excitation densities. Some trends in the strength of phonon co-operation are noted. In the case of Si_Ga-C_P pairs, sharp replicas of ZP pair lines with a momentum-conserving phonon are also resolved.Using the integral band decay technique and results from time-resolved spectroscopy we have determined the transition probabilities for the total luminescence band as well as for the ZP band for nearly all pairs mentioned. The influence of incomplete saturation of the pairs during excitation with a focussed beam of an argon-ion laser is discussed and approximately corrected for. Extrapolated to zero pair separation, the total transition probability ranges from ∽ 10⁵s^-1 for Si_Ga-C_P pairs to ∽ 15 × 10⁵s^-1 for O_P-C_P and O_P-Zn_Ga pairs. The ZP probability ranges from ∽ 4 × 10³s^-1 for Si_Ga-C_P and Si_Ga-Si_P pairs to ∽ 4 × 10⁵s^-1 for S_P-C_P pairs. The transition probability for pairs in GaP is discussed in relation to the site occupied by the donor and the depth of the centres involved. The relatively high dope concentrations used in some cases, ∽ 1 to 2 × 10¹⁸cm^-3, are discussed briefly in relation to “concentration quenching”.The temperature dependence of the luminescence intensity of S_P-Si_P pairs is satisfactorily analysed with a simple linear model. The same model is applied to similar literature data on the S_P-C_P pair luminescence. Using in addition data on the average pair transition probability, trapping rate constants for hole capture by the Si_P and C_P acceptors were calculated to be ∽ 10^-9 cm³s^-1. Evidence is presented that the trapping rate constant for holes by the Zn_Ga-O_P complex is about 2 × 10^-9 cm³s^-1.     

PrP_5O_(14)晶体中Pr~(3+)离子的f-d辐射跃迁

本文讨论了计算稀土离子4f~(N-1)5d-f~N辐射跃迁几率的一般方法,提出了这类跃迁的亲态选择定则。并在C_(2v)群对称下,具体计算了Pr~(3+)离子在PrP_5O_(14)晶体中的f-d辐射跃迁几率,结果指出稀土离子的f-d跃迁几率比f-f跃迁几率大得多。     

A unified treatment of the theory of donor-acceptor pair recombination emission

A general formalism for treating donor-acceptor pair emission is developed which highlights important differences between the spectra resulting from a random distribution of the donors and acceptors, and that resulting from a preferentially paired distribution. Application of the analysis to the donor-acceptor pair emission band observed in diamond shows that the properties reported are consistent with a marked preferential pairing of the donors and acceptors.     

Central cell effects in donor-acceptor pair spectra of polar semiconductors

The central cell effect in donor-acceptor (DA)-pair spectra is calculated by means of a semi-empirical short range potential and within the effective mass approximation (EMA). The electron-hole recombination energy is determined variationally as a function of the (DA)-pair separation R. The results are compared with previous theoretical work and with experiment in the case of ZnSe with In-donor and Li-acceptor dopants.     

A remark on transition probability

Uhlmann's transition probability P(ψ, φ) of two normal states of a von Neumann algebra M, which is the supremum of |(Ψ, Φ)|² for all possible choices of representative vectors Ψ and Φ of ψ and φ, is shown to be the infimum of (∫d(μ_{ψ, e})^1/2)² for the induced measures μ_{ω, e}(B)=ω(e(B)) (B: Borel set in ℝ, ω=ψ, φ) for all possible projection-valued measures e belonging to M.     

Influence of electron-phonon coupling on the energy of an exciton bound to a donor-acceptor pair

The influence of electron-phonon coupling on the binding energy of excitons bound to donor-acceptor pairs is investigated. It is shown that the experimental data in ZnSe agree very well with a theory which takes into account Coulomb overlap and the configuration interaction. The contribution of electron-phonon coupling is small, but not negligible.     

Influence of conducting nanocylinder on resonance energy transfer in donor-acceptor pair of molecules

We propose a mathematical model of nonradiative electronic excitation energy transfer between donor and acceptor molecules near the surface of an infinitely long conducting nanocylinder by means of surface plasmons. We reveal that, under resonance conditions, the rate of transfer increases compared to the case of the absence of the conducting cylindrical surface. The dependence of the energy transfer rate on configurational parameters system is found.     

Cooper pairs and the gas-liquid transition

The question whether the gas-liquid phase transition occurs in the many-Cooper pair system is studied. When the idea of Yang-Lee zeros is applied to the grand partition function equivalent to the BCS model, its impossibility is proved.     

Study of acceptor states in CdTe by donor-acceptor pair excitation luminescence

Excitation of donor-acceptor pair luminescence has been studied in CdTe doped with lithium or chlorine. The excitation spectrum of the lithium acceptor is determined and fitted with the effective mass theory of Baldereschi and Lipari. Revised values of the valence band parameters are deduced: μ = 0.8, δ = 0.054, Ry = 24 meV. The analysis of the 1.45 eV luminescence band in compensated Cl-doped crystals shows the existence of donor-acceptor pair transitions. Three acceptor centers are identified: E_A = 89, 111 and 119 meV, and the contribution of a deep donor (E_D > 40 meV) is demonstrated. Besides intracentre type excitation transitions of the 1.45 eV band have been observed in non-compensated chlorine-doped crystals. Thus several recombination channels and distinct acceptor states contribute to the composite 1.45 eV luminescence band.     

The nuclear-structure dependence of radiative corrections in superallowed Fermi beta-decay

We give a shell-model calculation of the nuclear-structure-dependent axial-vector contribution of the Born graphs to the radiative correction in superallowed Fermi β-decay. The impact of the correction is to give a modest improvement in the test of the conserved-vector-current (CVC) hypothesis, and a slightly smaller value of the quark-mixing matrix element, V_ud. The test of the unitary of the first row of the Kobayashi-Maskawa matrix gives: V_ud² + ν_us² + V_ub² = 0.9962 ± 0.0016, violating the three-generation standard model. Hints from neutron-only data suggest that nuclear-structure corrections in superallowed Fermi β-decay are still not fully under control.     

The effect of orbital relaxation on transition energies in radiative opacity calculations

The neglect of orbital relaxation in average-atom opacity calculations is investigated for the case of K-shell photoexcitation and photoionization in a chlorine plasma.     

Flavor dependence of spontaneous pair creation

In superstring models, contributions to the muon longitudinal polarizationP _L in the decay \(K_L \to \bar \mu \mu \) can arise from interactions involving the exoticD andD ^c superfields. It is shown that these interactions also contribute to the decay μ→eγ. After using the experimental limit to constrain this process, we find thatP _L arising from these new interactions is less than 10^?4.