摘要:

The basic features of the photorefractive effect in oxide materials are outlined and the required knowledge on defects in such compounds is defined. The central question is: Between what charge states of what defects does an inhomogeneous light pattern redistribute charges in a photorefractive crystal? The joint investigation of light-induced EPR and optical absorption changes is introduced as a very useful method to answer this question, also for EPR-silent defect valencies and also at room temperature. Examples for the application of the method are given and its scope is discussed.

ISSN:1042-0150    

DOI:10.1080/10420159908230124

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The two-photon excitation line shapes of f-f transitions of Eu2+in KMgF3have been investigated as a function of temperature. Results for several transition lines of the6PJand6DJmultiplets are presented in this work. The two-photon excited transitions appear as zero-phonon lines with a Lorentzian profile whose peak energy is shifted from the zero temperature position. The observed temperature dependence of the zero-phonon line shapes is ascribed to the elastic scattering of the electronic transitions among vibrational states via anharmonic coupling to a phonon mode of the lattice heat-bath. In those components of 4f7multiplets whose energies are not resonant with the 4f65d broad excited state, a direct proportionality to the phonon occupation number of the coupled mode is found for the line-shapes and peak-positions temperature dependences.

ISSN:1042-0150    

DOI:10.1080/10420159908230125

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The reflection spectrum as well as the excitation spectrum of self-trapped exciton emission at 2.6 eV has been measured in a NaF crystal at 5 K. The width of a forbidden band equals approximately 12.3 eV.

ISSN:1042-0150    

DOI:10.1080/10420159908230126

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Here, we present a study of exciton behaviour in LaPO4doped with trivalent cerium and/or terbium ions. In undoped LaPO4excited at 155 nm a weak emission is observed at 260 nm. The same emission is also detected in the weakly cerium or terbium doped samples. This emission is probably due to self-trapped exciton (STE). It matches exactly the 4f → 5d absorption band of cerium ions leading to an efficient energy transfer. The nature of this transfer, radiative and/or non-radiative, is analysed. In terbium doped sample the energy transfer from the STE exists but seems to be less efficient. This is essentially due to the fact that the STE emission overlaps terbium 4f → 4f transitions, the oscillator strengths of which are much weaker.

ISSN:1042-0150    

DOI:10.1080/10420159908230127

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In the nonstoichiometric X-ray storage phosphor BaF1.1Br0.9a new intrinsic hole centre was found by electron paramagnetic resonance (EPR). It is the anticentre of the F(Br−) centre with which it is generated simultaneously by X-irradiation. Bleaching into the F(Br−) band destroys it. From the simulation of the power EPR spectrum and the generation mechanism the hole centre is thought to be an H(F−2,F) centre. Magic angle spinning nuclear magnetic resonance (MAS-NMR) revealed that the F excess in non-stoichiometric BaF1.1Br0.9is due to F−on Br−sites, i.e. F−antisites. The generation of F(Br−) electron trap-hole trap pairs upon X-irradiation originates at the F−antisites.

ISSN:1042-0150    

DOI:10.1080/10420159908230128

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The dependence of the thermoluminescence (TL) intensity on the irradiation temperature (Tirr) was examined separately for the various TL peaks in the temperature range 450–700 K. One TL peak at 520 K was found to depend only slightly onTirr. A TL peak at 460 K energed above RT rising fast withTirrin the temperature range 200–300 K and dropping in intensity above 300 K. This TL peak was found to rise quardratically with the dose. The TL Peaks above 600 K showed a considerable rise withTirr. These peaks rose only slightly supralinearly at low doses and with the square of the dose at high doses. A model is proposed to explain the above effects.

ISSN:1042-0150    

DOI:10.1080/10420159908230129

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The mechanism of Photo-stimulated Luminescence (PSL) is investigated in copper and europium doped KCl. Electron Paramagnetic Resonance, Photoluminescence, and X-ray Photoelectron Spectroscopy measurements were performed on powdered samples of KCl: Cu+and KCl: Eu2+, γ-irradiated at room temperature. Our results show that the charge state conversion of Cu+to Cu2+does not take place after γ-irradiation in KCl: Eu2+, even though a significant reduction in Eu2+concentration is detected after γ-irradiation, the PSL is not due to Eu3+-F recombination. The energy transfer from recombination process involving F centers to the activator ions Cu+and Eu2+in KCl seems to cause the PSL in these materials.

ISSN:1042-0150    

DOI:10.1080/10420159908230130

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

KTaO3crystals slightly doped with iron were investigated by luminescence spectroscopy. A zero-phonon line was found in the low-temperature emission at 14569 cm−1under excitation in the spectral region 15000–24000 cm−1. The results suggest that this luminescence originates from Fe3+(d5) ions substituted for K+. The excitation and emission are assigned to the6A1(S) →4T1(G),2T2(I),4T2(G), and4T1(G) →6A1(S) transitions, respectively. The following crystal field parameters of Fe3+in KTaO3were found:Dq= 1230 cm−1B= 690 cm−1, andC= 3452 cm−1.

ISSN:1042-0150    

DOI:10.1080/10420159908230131

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The non-linear optical crystal Bi2TeO5is a good host for several cations with segregation coefficients close to or larger than unity. Bi2TeO5: Er was the first rare earth doped crystal that was grown and studied. Eight Er3+related transitions were identified in the absorption spectra, from the4I15/2ground state. All the expected Stark components of the observed transitions were detectable at 10 K. Further splitting of the lines related to the different Bi sites occupied by Er. Excitation from higher Stark levels of the ground state was detected at 200 K and above. Erbium related luminescence was observed in the doped crystals after photo-excitation of the4F5/24F7/22H11/2and4S3/2levels.

ISSN:1042-0150    

DOI:10.1080/10420159908230132

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Cathodoluminescence (CL) and infrared (IR) absorption of silica samples with normal stoichiometry as well as with an extremely high level of oxygen deficit were studied. Additionally, the samples have been treated or non-treated in hydrogen at 800°C. Crystalline quartz was used as reference of the luminescence energetic yield determination and revealing of the glassy state role in defect production under electron beam. The luminescence spectra of silica show the red band at 1.85 eV due to non-bridging oxygen and the two bands at 2.7 and 4.4 eV due to twofold-coordinated silicon. The energetic yield for CL is about 0.1%, for X-ray excited luminescence (XL) it approaches to 0.15%. CL of quartz at low temperatures possesses the self-trapped exciton luminescence mainly. Under electron beam irradiation there occurs production and destruction of luminescence centers in glass, whereas X-ray excitation mainly leads to electron and hole recombination on existing centers. After hydrogen treatment the IR spectra show the appearance of Si-H and Si-O-H vibration bands, independent of the oxygen deficiency. The hydrogen treatment strongly affects the cathodoluminescence properties of oxygen deficient silica by modifying the luminescence centers themselves.

ISSN:1042-0150    

DOI:10.1080/10420159908230133

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor