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1.
The composition of gadolinium-scandium-aluminium (GSAG) and yttrium-scandium-aluminium (YSAG) garnet crystals grown by the Czochralski method and by floating zone melting was analysed. It is shown that Sc3+ and Al3+ ions in GSAG and Y3+, Sc3+ and Al3+ ions in YSAG can simultaneously occupy two types of sites in the lattice. The congruent melting composition of GSAG is {Gd2.88Sc0.12} [Sc1.77Al0.23] (Al3)O12. The homogeneity range of GSAG is rather narrow. In the Y2O3-Sc2O3-Al2O3 system a wide range of garnet-structured solid solutions exist. However, there is no ternary garnet that melts congruently. Distribution coefficients of components in YSAG are slightly varied from unity in the whole concentration range, and as the melt composition approaches YAG they tend to unity. Cr3+ and Nd3+ distribution coefficients in GSAG and YSAG are presented. 相似文献
2.
This paper describes measurements of the R-line emission from Cr 3+ ions in Y 3Ga 5O 12, Gd 3Sc 2Ga 3O 12, and Gd 3Sc 2Al 3O 12. Discrete splittings of the lines are interpreted as due to disorder on the cation sublattices. Assuming statistical distributions of the cations on the different cation sublattices enables estimates to be made of the degree of non-stoichiometry in the crystals. 相似文献
3.
We examine the oscillator strengths and the intensity parameters Ω
t
( t = 2, 4, 6) of yttrium-aluminum, scandium-containing, and gallium garnet crystals doped with Er 3+ ions. A comparative analysis of the oscillator strengths and the intensity parameters Ω
t
( t = 2, 4, 6) of garnets with different contents of Al 3+ and Sc 3+ ions (Gd 2.4Er 0.5Sc 1.8Al 3.3O 12, Gd 2.4Er 0.5Sc 1.9Al 3.2O 12, Gd 2.4Er 0.5Sc 2.0Al 3.1O 12) is performed, as a result of which the oscillator strengths and the intensity parameters Ω
t
( t = 2, 4, 6) of these crystals are shown to have close values. We find that Ca 3(NbGa) 5O 12 crystals doped with Er 3+ ions are characterized by highest values of the oscillator strengths for hypersensitive transitions and of the intensity
parameter Ω 2 of Er 3+ ions compared to the values of these quantities in the examined garnet crystals, which is determined by the fact that the
symmetry of the local environment of Er 3+ ions in these crystals is C
1, C
2, or C
2ν. We reveal that, as the concentration of Er 3+ ions in these crystals increases from 1 to 39 at %, both the oscillator strength of the hypersensitive transition 4
I
15/2 → 2
H
11/2 of Er 3+ ions and their intensity parameter Ω 2 tend to decrease, which can be related to an increase in the relative fraction of Er 3+ ions with higher symmetry of the local environment. 相似文献
4.
The emission and excitation spectra of Cr 3+ -doped Gd 3Ga 5O 12 (GGG) and Gd 3Sc 2Ga 3O 12 (GSGG) are explained in the light of multisite effects. The situation is particularly complicated in the case of GSGG, where the different sites have 2E energy levels near each other which overlap with the 4A 2 → 4T 2 absorption bands. The spectra obtained under selective excitations are interpreted on the multisite assumption. 相似文献
5.
Photoluminescence of undoped and Cr 3+-doped β-Ga 2O 3 was investigated. The transparent, undoped β-Ga 2O 3 film was successfully prepared by thermal conversion from GaOOH. The film exhibited predominant green luminescence in response to ultraviolet light excitation at 250 nm. This luminescence behavior, which was proposed to result from the oxygen defect centers, was used in examining excitation and emission mechanisms for Cr 3+ ions doped in β-Ga 2O 3. It was found that red luminescence of Cr 3+ surpasses green luminescence of the host lattice, as evidenced by the dependence of the spectral structure on the Cr 3+ concentration. The excitation of Cr 3+ was then suggested to be caused by the energy transfer from Ga 3+O 6 octahedra present in the monoclinic β-Ga 2O 3 lattice. 相似文献
6.
On the basis of the 120×120 complete energy matrices for a d 3 configuration ion in a trigonal ligand field, for Cr 3+ ions doped in MgTiO 3 and LiTaO 3, the local structures and EPR g factors of the octahedral (CrO 6) 9− clusters have been studied, respectively. By simulating the calculated optical spectra and the EPR spectra data to the experimental results, local structure parameters are obtained. The calculated results show that although the local lattice structures around the M (M=Mg 2+, Ta 5+) ions are obviously different, after Cr 3+ replacing the M, the local lattice structures around the Cr 3+ ions are quite similar and close to those of the Cr 2O 3. This may be ascribed to the fact that the octahedral Cr 3+ center in MgTiO 3:Cr 3+ and LiTaO 3:Cr 3+ systems and that in Cr 2O 3 exhibit similar octahedral (CrO 6) 9− clusters. Moreover, the corresponding theoretical values of the optical spectra have been reported. It is also found that the orbital reduction factor k is very important to understand the EPR g factors for Cr 3+ ions doped in MgTiO 3 and LiTaO 3. 相似文献
7.
Zinc phosphate glasses doped with Gd 2O 3:Eu nanoparticles and Eu 2O 3 were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P 2O 5 glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu 3+ ions has been observed when Eu 2O 3 is incorporated in ZnO-P 2O 5 glasses. Lack of energy transfer from these defect centres to Eu 3+ in Gd 2O 3:Eu nanoparticles doped ZnO-P 2O 5 glass has been attributed to effective shielding of Eu 3+ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu 3+ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd 2O 3:Eu nanoparticles or Eu 2O 3 incorporation. 相似文献
8.
The emission and excitation spectra of Cr 3+ -doped Gd 3Ga 5O 12 (GGG) and Gd 3Sc 2Ga 3O 12 (GSGG) are explained in the light of multisite effects. The situation is particularly complicated in the case of GSGG, where the different sites have 2E energy levels near each other which overlap with the 4A 2 4T 2 absorption bands. The spectra obtained under selective excitations are interpreted on the multisite assumption. 相似文献
9.
The coexistence of sharp R-lines from the 2
E state and the broad band from the 4
T
2 state in the photoluminescence spectra of Cr 3+:Gd 3Sc 2Ga 3O 12 (GSGG) and Cr 3+:Y 3Ga 5O 12 (YGG) is observed at low temperature (10K). The decay lifetimes of the broad emission bands of Cr 3+ in GSGG and YGG are very close to those of the R-lines being, respectively, 0.23 ms and 2.5 ms. These results are explained in terms of the extent of the mixing of the 4
T
2 vibronic wavefunction with that of the 2
E lowest excited state by tunnelling. 相似文献
10.
The optical absorption spectra (d-d transition bands) and covalent effect of Ni 2+ ions in octahedral sites of Ca 3Sc 2Ge 3O 12 crystal have been investigated by the full energy matrix based on the two spin–orbit coupling parameters model. The bond length of octahedral site is Ri?=?2.19 Å, which can be determined by the cubic crystal-field parameter and optical spectral data. The lattice distortion of the Ni 2+ center in Ca 3Sc 2Ge 3O 12 crystal is also obtained from the calculations. In addition, the result has shown that the covalent effect of Ni 2+ ion in the octahedral site of Ga 3Sc 2Ge 3O 12 is obvious and cannot be ignored. The calculated d-d transition bands agree well with that of the experimental findings, suggesting that the present methods can explain reasonably the optical spectral data and covalent effect of 3d 8 ions in octahedral lattices. 相似文献
11.
In this paper we report on the optical properties of triply Cr 3+, Er 3+, and RE 3+ (RE=Tm, Ho, Eu) doped Gd 3Ga 5O 12 crystals that were grown by the Czochralski method. Optical absorption, near-infrared (NIR), and mid-infrared (mid-IR) fluorescence spectra were characterized for the fabricated crystals and corresponding luminescence decay measurements under 654 nm excitation were also carried out. Based on the analysis of energy transfer process between Er and RE (RE=Tm, Ho, Eu) ions, the energy transfer efficiency (ETE) values were evaluated, correspondingly. From the spectral data of all the studied crystals, it is observed that the co-doped Cr 3+ ion highly increases the absorption pump power and the three kinds of co-doped RE 3+ ions depopulate the Er: 4I 13/2 energy level effectively. The spectral analysis shows that titled rare earth doped crystals are promising materials for ~3.0 μm mid-IR laser applications and among them Cr,Er,Eu:GGG is relatively more suitable due to its excellent optical properties compared with others. 相似文献
12.
Binary (ZnO) 0.5(P 2O 5) 0.5 glasses doped with Eu 2O 3 and nanoparticles of Gd 2O 3:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO) 0.5(P 2O 5) 0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na 2O-SiO 2 glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu 3+ ions leading to improved Eu 3+ luminescence from such glasses. Based on the decay curves corresponding to the 5D 0 level of Eu 3+ ions in both Gd 2O 3:Eu nanoparticles incorporated as well as Eu 2O 3 incorporated glasses, a significant clustering of Eu 3+ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO) 0.5(P 2O 5) 0.5 glass doped with Gd 2O 3:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu 3+ ions. Poor energy transfer from the defect centres to Eu 3+ ions in Gd 2O 3:Eu nanoparticles doped (ZnO) 0.5(P 2O 5) 0.5 glass has been attributed to effective shielding of Eu 3+ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu 3+ ions. 相似文献
13.
Crystals of lutetium gadolinium garnet solid solutions (Lu 1 − x
Gd
x
)Al 5O 12 (0 ≤ x ≤ 0.6) doped with Ce 3+ and Pr 3+ ions have been prepared by the horizontal directional crystallization method, and their optical and luminescence properties
have been investigated. It has been established that the introduction of gadolinium into the lutetium garnet lattice leads
to a decrease in the antisite luminescence (Lu Al centers) in the UV spectral range and to sensitization of the Ce 3+ ion luminescence. By contrast, the presence of gadolinium results in the quenching of the Pr 3+ luminescence due to the nonradiative excitation transfer from Pr 3+ ions to Gd 3+ ions. 相似文献
14.
The color rendering index (CRI) and structural stability of cerium doped yttrium aluminum garnet (YAG:Ce) based phosphors have been enhanced by replacing Y 3+ ions by larger radius ions (Tb 3+, Gd 3+, Eu 3+, and Sm 3+) at the dodecahedral site and replacing Al 3+ ions by larger ones (Ga 3+, Y 3+, Tb 3+, Gd 3+, and Sm 3+) at the octahedral site. These aluminum garnet crystalline powders were prepared by solvothermal reaction method at 300 °C for 48 h. The lattice constant values of synthetic aluminum garnet crystalline powders are larger than that of YAG and the emission wavelength of Ce 3+ ion of these samples is longer than that of YAG:Ce. FESEM and TEM studies revealed that the Ln 3Ga 2Al 3O 12 and Ln 3Al 2Al 3O 12 crystalline powders have 3-dimensional star-like morphology with submicron size and good crystallinity, while, Ln 3(LnAl)Al 3O 12 garnet crystalline powders were cubic crystalline phases and shaped as cubes with the round edge having an approximate diameter of about 200–400 nm. All the prepared powders were grown along (100) direction and crystallized into single crystal. Also, the effects of treatment time and reaction temperature on the structure of aluminum garnet crystalline powders have been investigated. 相似文献
15.
The luminescent characteristics of Li 2O-B 2O 3-P 2O 5-CaF 2 (LBPC) glasses doped with Gd 3+ and Tb 3+ ions and codoped with Ce 3+ are studied by pulsed optical spectrometry under electron beam excitation. It is found that in glass with Ce 3+ and Gd 3+ ions a decrease in the decay time of gadolinium luminescence in the 312-nm band ( 6 P J → 8 S 7/2) was observed. It is shown that in the glass LBPC: Tb, Ce, an increase in the emission intensity in the main radiative transitions in terbium ion was observed. In the kinetics of luminescence band 545 nm of LBPC: Tb, Ce glasses, is present stage of buildup, the character of which changes with the doped of Ce 3+ ions. The mechanism of energy transfer in LBP glasses doped with rare elements is discussed. 相似文献
16.
The silicates Ca 3Sc 2Si 3O 12, Ca 3Y 2Si 3O 12 and Ca 3Lu 2Si 3O 12, both undoped and doped with Pr 3+ ions, have been synthesized by solid-state reaction at high temperature. The luminescence spectroscopy and the excited state dynamics of the materials have been studied upon VUV and X-ray excitation using synchrotron radiation. All doped samples have shown efficient 5d-4f emission upon direct VUV excitation of 5d levels, but only Ca 3Sc 2Si 3O 12:Pr 3+ shows luminescence upon interband VUV or X-ray excitation. The VUV excited emission spectra of Ca 3Y 2Si 3O 12:Pr 3+ and Ca 3Lu 2Si 3O 12:Pr 3+ show features attributed to emission from two distinct sites accommodating the Pr 3+ dopant. The decay kinetics of the Pr 3+ 5d-4f emission in Ca 3Sc 2Si 3O 12:Pr 3+ upon VUV excitation across the band gap are characterized by decay times in the range 25-28 ns with no significant rise after the excitation pulse. They appear to be faster upon X-ray irradiation than for VUV excitation. Weak afterglow components are attributed to defect luminescence. 相似文献
17.
The cation distribution has been studied with 57Fe Mössbauer spectroscopy in the garnet system Eu 3?ySc 2+yFe 3O 12 with y = 0.0, 0.2 and 0.5. It is shown that the previously proposed cation distribution is not correct. The problem of possible impurities in the investigated system is discussed in detail. Several possible cation distributions are considered compatible with Mössbauer data. Mössbauer results combined with the composition dependence of lattice constants show that the tetrahedral sites are accessible to Sc 3+ ions. The system studied is a second example of a garnet structure in which Sc 3+ ions are found at the tetrahedral sites. A small fraction of Sc 3+ ions for the samples y = 0.2 and 0.5 is also found at the dodecahedral sites. 相似文献
18.
The thermal shifts of R1 and R2 lines of Cr 3+-doped garnets Y 3Ga 5O 12 (YGG), Y 3Sc 2Al 3O 12 (YSAG) and Gd 3Sc 2Al 3O 12 (GSAG) are studied by considering both the static contribution (which is frequently neglected in the previous papers) due to lattice thermal expansion and the vibrational contribution due to electron–phonon interaction. In the studies, the static contribution is calculated with the thermal expansion coefficient of the corresponding cluster in the host garnet crystals. The results indicate that the static contributions in sign are opposite to and in magnitude are about 10% of the corresponding vibrational contributions. The true electron–phonon coupling parameters α′ obtaining by taking both contributions into account increase more than 10% in comparison with the corresponding apparent electron–phonon coupling parameters α determined by considering only the vibrational contribution in the previous paper. So, to obtain the complete understanding of thermal shift of a spectral line and the true rather than apparent electron–phonon coupling parameters, one should take account of both the static and vibrational contributions. 相似文献
19.
The superionic conductivity and dielectric response of heavily doped fluorite-structured Ba 1−xR xF 2+x (R=La, Pr, Nd, Gd, Tb, Y, Sc; x=0.005–0.45) crystals are reported. The highest ionic conductivity is found for R=Sc and x=0.1.
Upon ScF 3 doping, small Sc 3+ ions rearrange their surroundings, create excessive fluoride interstitial ions and bring about a high ionic conductivity.
For each dopant, the concentration dependence of the ionic conductivity is non-linear. A monotonous concentration dependence
of the ionic conductivity is found only for La 3+ doping. Upon doping with Nd 3+, Gd 3+, Tb 3+, Y 3+ and Sc 3+ ions, a conductivity maximum is observed at x=0.1–0.2. Upon Pr 3+ doping, this maximum is split. The influence of defect clustering on the concentration dependence of the conductivity is
discussed.
Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999. 相似文献
20.
Mössbauer absorption spectra have been measured for Cr 3+ doped Al 2O 3?Fe 2 57 O 3 systems for different values of the Cr 3+ concentration at room temperature. The cross relaxation between Fe 3+ and Cr 3+ ions, which destroys the paramagnetic hyperfine structure of Fe 57 observed in undoped Al 2O 3?Fe 2 57 O 3, is thoroughly studied. The experimental results suggest a new kind of cross-relaxation process involving three spins, i.e. two Fe 3+.ions and one Cr 3+. The process, though it is a higher-order one, is highly effective because it is energy-conserving. 相似文献
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