Sensitization in CaS:Bi:Tm phosphors

The emission spectra of calcium sulphide phosphors activated with bismuth, thulium, and both together are studied in the spectral range of 4000 Å to 8000 Å. The results indicate resonance transfer of excitation energy from Bi to Tm. Sensitizer to sensitizer transfer also appears to be appreciable. A plausible energy level diagram is proposed to explain the sensitization mechanism.     

LiNbO_3:In:Fe:Cu晶体中的双波长非易失存储

为了提高晶体的非易失存储性能,采用双波长存储技术实验研究了LiNbO3:In:Fe:Cu晶体中的非易失存储,折射率调制度为1.04×10-4,记录灵敏度达到0.965 cm/J.与传统的双色非易失记录相比,该方法大幅度地提高了光栅的强度和记录的灵敏度.利用Kukhtarev带输运模型对双波长非易失记录过程中光栅的动态演化过程进行了数值模拟,同时讨论了氧化还原程度对双波长非易失全息记录的影响.理论与实验符合的较好.     

Photoluminescence processes in LaOCl:Bi and YOCl:Bi

The luminescence of rare earth oxychlorides LnOCL:Bi (with Ln = La and Y) is studied in detail. The main excitation bands, responsible for the blue and UV fluorescences, are attributed to the bismuth activator substituting for Ln³⁺ in the rare earth tetragonal site. The weak shoulder of these bands and the complex decay times are assumed due to a parasitical phase, La₂O₃ or Y₂O₃ doped by bismuth, an X-ray analysis confirming their presence in the samples. Finally, the existence of these phases does not seem to have an important effect upon the interpretation of the luminescence processes of the main center, as shown by the configuration curve model.     

Laser phenomena in DCEL of ZnS:Cu:Nd:Cl thin films

The possibility of the occurrence of laser phenomena in the DCEL of thin films of ZnS:Cu:Nd:Cl, designed for display purposes, has been investigated. Evidence of stimulated emission at ～ 1080 nm has been found in both DCEL and cathodoluminescence emission of the films and has been attributed to a tendency to population inversion involving the ${}^4\text{F}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ energy level and a sub-level of the ${}^4\text{I}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ energy level. In addition, the expected directional nature of the stimulated emission has been shown to be present at the higher applied voltages.     

Multiplexing holograms in LiNbO3:Fe:Mn crystals

Persistent holograms are recorded with red light in lithium niobate crystals doped with manganese and iron. Different erasure mechanisms are investigated, and a recording schedule for multiplexing holograms with equal diffraction efficiencies is proposed. To test the recording schedule experimentally, we multiplex 50 plane-wave holograms with the proposed recording schedule.     

Microwave-induced optical nuclear polarization in Si:P:B

The first successful experiments of microwave-induced optical nuclear polarization in compensated silicon are presented. Bound holes are created at the boron sites using band-gap light of 1.047 μm. Subsequently, the high spin polarization of these bound holes is transferred to the ²⁹Si nuclei using microwave irradiation, resulting in an enhancement of the nuclear magnetic resonance signal. It is shown that a long lifetime of the nuclear spin polarization thus created is obtained, once the excitation light is shut off.     

Exclusive processes in QCD:: Two-photon physics involving baryons

Exclusive two-photon processes involving baryons have been calculated within the framework of perturbative QCD. In particular, the angular dependence of the process $\text{γγ →}\text{p}\text{p}$ is predicted as a function of the universal baryonic distribution amplitudes φ(x_i). The overall normalization is then found by a comparison with the process $\text{Ψ →}\text{p}\text{p}$, so that we can present a unique, absolutely normalized QCD prediction for the two-photon processes. We argue that these predictions, based on the $\text{Ψ →}\text{p}\text{p}$ decay rate, should be more reliable than those based on baryonic form factors. Presently not enough data exist to give a meaningful differential cross section for the process $\text{γγ →}\text{p}\text{p}$. Nevertheless, a total cross section has been obtained. Excluding the region close to threshold, quite good agreement between our predictions and experimental data is found. The analysis in this paper is trivially generalized to other baryons as well.     

Perspectives in magnetics: Italy

A review is given of fundamental research in magnetics pursued in Italian universities and laboratories of Consiglio Nazionale delle Ricerche. The main topics covered are in the field of soft materials, hard materials and garnets. The electronic structure of metals is investigated by polarized neutron diffraction, while studies of domain wall motion provide the basis for fully understanding power loss processes and mechanisms. Work on amorphous magnetism has focused in particular on the study of short range order in these materials. Most fundamental research on hard materials is directed toward permanent magnet applications, microwave devices and magnetic recording. Magnetization processes are a major subject of investigation in these materials, with applications both to hexagonal ferrites and rare earth-3d metal compounds. The crystal chemistry of garnets is being pursued by carrying out a variety of metal substitutions and studying site occupancies and valence states in both bulk materials and LPE films. The static and dynamic properties of domains are also investigated for display and memory applications in addition to microwave properties and materials.     

Introduction: optimization in networks

The recent surge in the network modeling of complex systems has set the stage for a new era in the study of fundamental and applied aspects of optimization in collective behavior. This Focus Issue presents an extended view of the state of the art in this field and includes articles from a large variety of domains in which optimization manifests itself, including physical, biological, social, and technological networked systems.     

Photoluminescence in heavily doped Si: B and Si: As

We report the results of low-temperature photoluminescence measurements on a series of heavily-doped Si: As and Si: B samples. New spectra are obtained for very high doping levels (10¹⁹ 2- 10²⁰ cm^-3), and the results for the more lightly doped samples are found to be in good agreement with previously published data. By comparing the luminescence of a Si: As sample before and after partial compensation with B, we verify that minority carriers can be localized even in “metallic” samples.     

Ferromagnetism in GaN:Gd: a density functional theory study

First-principle calculations of the electronic structure and magnetic interaction of GaN:Gd have been performed within the generalized gradient approximation (GGA) of the density functional theory with the on-site Coulomb energy U taken into account (also referred to as GGA+U). The ferromagnetic p-d coupling is found to be over 2 orders of magnitude larger than the s-d exchange coupling. The experimental colossal magnetic moments and room-temperature ferromagnetism in GaN:Gd reported recently are explained by the interaction of Gd 4f spins via p-d coupling involving holes introduced by intrinsic defects such as Ga vacancies.     

Strain-induced effects in H: Ti: LiNbO3 single-crystal layers

The parameters of proton-exchange waveguide H: LiNbO₃ layers and doubly doped H: Ti: LiNbO₃ layers were comparatively analyzed by x-ray diffractometry and optical mode spectroscopy. It was established that the change in the lattice parameter in hybrid H: Ti: LiNbO₃ layers is significantly smaller than that in proton-exchange H: LiNbO₃ layers formed under the same proton exchange conditions. The behavior of the optical and structural parameters of H: Ti: LiNbO₃ layers was studied in a wide hydrogen concentration range.     

Alpha:2n:alpha molecular band in 10Be

The 10.15 MeV resonance in 10Be has been probed via resonant 6He+4He elastic scattering. It is demonstrated that it is the Jpi=4+ member of a rotational band built on the 6.18 MeV 0+ state. A Gammaalpha of 0.10-0.13 MeV and Gammaalpha/Gamma=0.35-0.46 were deduced. The corresponding reduced alpha width, gamma2alpha, indicates one of the largest alpha-cluster spectroscopic factors known. The deformation of the band, including the 7.54 MeV, 2+ member, is large (h2/2I=200 keV). Such a deformation and the significant degree of clusterization signals a well-developed alpha:2n:alpha molecular structure.