共查询到20条相似文献,搜索用时 47 毫秒
1.
Traditional ligand-field theory has to be improved by taking into account
both “pure electronic” contribution and electron-phonon interaction one
(including lattice-vibrational relaxation energy). By means of improved
ligand-field theory, R1, R2, R'3, R'2, and R'1
lines, U band, ground-state zero-field-splitting (GSZFS) and ground-state g
factors as well as thermal shifts of R1 line and R2 line of YAG:Cr3+ have been calculated. The results are in very good agreement with the experimental data. In contrast with ruby, the octahedron of ligand oxygen ions surrounding the central Cr3+ ion in YAG:Cr3+ is
compressed along the [111] direction. Thus, for YAG:Cr3+ and ruby,
the splitting of t234A2 (or t232E) has opposite order,
and the trigonal-field parameters of the two crystals have opposite signs.
In thermal shifts of R1 and R2 lines of YAG:Cr3+, the
temperature-dependent contributions due to EPI are dominant. 相似文献
2.
By using strong-field scheme, the complete d5 energy matrix with symmetry has been constructed. Then, by diagonalization of this matrix at normal and various pressures,the whole energy spectrum [including the ground-state zero-field splitting (GSZFS)] and its pressure-induced shift (PS) of Znlb:Mn2+ have uniformly been calculated. The results are in very good agreement with experimental data. According to the eigenfimctions and PS, the assignments of four absorption bands have been given. By taking into account the dect of different deformations of t2 and e radial wavefunctions on t23(4A2)e2(3A2)4 A1 and t23(2E)e2(3A2)4E, the position of the third absorption band at normal pressure has been estimated.The tetragonal field is important for GSZFS of ZnTe:Mn2+ and its PS, which supports the existence of tetragonal Jahn-Teller distortion in ZnTe:Mn2+ The physical essentials of typical levels, GSZFS and their PS have been revealed. 相似文献
3.
Traditional ligand-field theory has to be improved by taking into account
both pure electronic contribution and electron-phonon interaction one
(including lattice-vibrational relaxation energy). By means of improved
ligand-field theory, the R line,
t23 2T1 and t23 2T2
lines, t22 (3T1)e4T2, t22 (3T1)e4T1 and t2
e2(4A2)4T1 bands, g factors of t23 4A2 and t23 2E, four strain-induced level-splittings and R-line thermal shift of
MgO:V2+ have been calculated. The results are in very good agreement with the experimental data. It is found that for
MgO:V2+, the
contributions due to electron-phonon interaction (EPI) come from the
first-order term; the contributions from the second-order and higher terms
are insignificant. In thermal shift of R line of MgO:V2+, the
temperature-dependent contribution due to EPI is dominant. The results
obtained in this work may be used in theoretical calculations of other
effects of EPI. 相似文献
4.
By using strong-field scheme, the complete d5 energy matrix with D2d symmetry has been constructed. Then, by diagonalization of this matrix at normal and various pressures,the whole energy spectrum [including the ground-state zero-field-splitting (GSZFS)], its PS and the g factor of the ground state for zns:Mn2+ have uniformly been calculated. According to the eigenfunctions and PS, the new assignments of five absorption bands have been given.The variation of tetragonal field with pressure makes a main contribution to the pressureinduced shift (PS) of GSZFS of zns:Mn2+, which supports the existence of tetragonal Jahn-Teller distortion in zns:Mn2+. It is found that when P≥62 kbar, t24(3T1)e4T1 merges with t2e4 2T2, which has to be taken into account in the calculation of PS of the fifth band in the range of 1 bar ~ 95 kbar. It is demonstrated that the Mn2+ ions in ZnS:Mn2+ have tetrahedral coordination, and the difference between ζ and ζ' caused by the covalency effect is very important for GSZFS. The physical essentials of typical levels, GSZFS and their PS have been revealed. By taking into account the influence of covalency on t23(4A2)e2(3A2)4A1 and t23(2E)e2(3A2)4E, the positon of the third absorption band at normal pressure has been estimated. 相似文献
5.
MA Dong-Ping 《理论物理通讯》2004,41(1):141-145
By means of both the theory for pressure-induced shifts
(PS) of energy spectra and the theory for shifts of energy spectra
due to electron-phonon interaction (EPI), at 300 K,
the `pure electronic' contributions and
the contributions from EPI to R1 line, R2 line, and U band of
GGG:Cr3+ as well as their PS have been calculated, respectively.
The total calculated results are in good agreement with all the
experimental data. Their physical origins have been explained.
It is found that the mixing-degree of |t22(3T1)e
4T2> and
|t232E> base-wavefunctions in the
wavefunctions of R1 level of GGG:Cr3+ is considerable
under normal pressure, and the mixing-degree rapidly decreases
with increasing pressure. The change of the mixing-degree with
pressure plays a key role for PS of
R1 line or R2 line. At
300 K, both the temperature-independent contribution to R1 line
(or R2 line or U band) from EPI and the temperature-dependent one
are important. The remarkable difference between pressure-dependent
behaviors of PS of R1 lines of GGG:Cr3+ and
GSGG:Cr3+ results
from the differences of their microscopic properties. The features
of emission spectra of
GGG:Cr3+ at various pressures have satisfactorily
been explained. 相似文献
6.
By means of improved ligand-field theory, the “pure electronic” presure-induced shifts (PS's) and the
PS's due to electron-phonon interaction (EPI) of the R1, R2,
B1, B2, B3, and R'3 lines and the ground-state zero-field-splitting of ruby have been uniformly calculated. The calculation results are in very good agreement with all the
experimental data. At normal pressure, ruby is a crystal with very
strong crystal field. Thus, the admixture of
|t22(3T1)e4T2〉and
|t322E〉bases in the wavefunction of R1 level of ruby is small at
normal pressure, and it gradually decreases with increasing pressure, which causes the R1-line PS of ruby to monotonously red shift with approximate linearity. The combined effect of the pure electronic PS of
R1 line and the PS of R1 line due to EPI gives rise to the total PS of R1 line. The analyses and comparisons among the features of R1-line PS's of three laser crystals (ruby,
GSGG:Cr3+ and
GGG:Cr3+) have been made, and the origin of their
difference has been revealed. 相似文献
7.
MA Dong-Ping CHEN Ju-Rong 《理论物理通讯》2005,44(6):1103-1114
By means of both the theory for pressure-induced Shifts (PS) of energy spectra and the theory for shifts of energy spectra due to electron-phonon interaction (EPI), the normal-pressure energy spectra of α and β centers of Cr^3+ ions for LLGG:Cr^3+ and the PS's of R1 lines and U band of these centers have been calculated at 10 K, respectively. The total calculated results are in very good agreement with the experimental data. For LLGG:Cr^3+, the pressureinduced low-high crystal-field transition and the reversal of R1-line PS take place. The pressure-dependent variation of Rmix^ei (2E - 4T2) [mixing-degree of (t2^2 (^3T1)e^4T2) and (t2^3 E) base-wavefunctions in the wavefunction of R1 state without EPI] plays a key role for the reversal of R1-line PS. The behavior of the pure electronic PS of R1 line is quite different from that of the PS of R1 line due to EPI. It is the combined effect of them that gives rise to the total PS of R1 line. The comparison between R1-line PS's of GSGG:Cr^3+ and LLGG:Cr^3+ has been made. It is found that a peak of R1-line PS appears at Rmix^ei (^2E - ^4T2) ≈ 0.08. 相似文献
8.
As a key factor leading to the pressure-dependent R1-line-shift reversal and R1-state lifetime, at 10 K, the pressure-dependent variation of mixing-degree of |t22(3T1)e4T2〉
and |t232
E〉base-wavefunctions in the wavefunction of R1 state of
LLGG:Cr3+ has been calculated and analyzed. From this, the physical origin of the pressure-dependent R1-line-shift reversal has been revealed. Furthermore, by using
the pressure-dependent values of the
sum of all square mixing-coefficients
of |t22(3T1)e4T2〉in the wavefunction of R1 state, the lifetimes of R1 state
of LLGG:Cr3+ at various pressures have been calculated, which
are in good agreement with observed results. The quantum anticrossing
effect between
t232E and t22(3T1)e4T2
levels due to both spin-orbital interaction and electron-phonon interaction is remarkable, which is related to the admixture of
|t22(3T1)e4T2〉and |t232
E〉as well as the low-high crystal-field transition. 相似文献
9.
By taking into account all the irreducible representations and
their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of basic wavefunctions within d3 electronic configuration, the values of the parameters in the expressions of thermal shift (TS) from EPI for the ground level, R level and R line of SrTiO3:Mn4+ have been evaluated; the R-line TS and various contributions to it have been calculated in the low-temperature region. It is found that all the three
terms of R-line TS from EPI relevant to the lattice vibration are red shifts. The Raman term is the largest, the neighbor-level term is the second, and the optical-branch term is very small
over the range of T≤80 K. The contribution to R-line TS from thermal
expansion has been approximately neglected in this work. The
very strong EPI relevant to its lattice vibration for
SrTiO3:Mn4+ causes its R-line TS to be an unusually large red-shift. Only by taking into account the strong softening of the low-frequency acoustic modes of the lattice vibration at low temperatures, can we successfully explain the variation
of R-line TS of SrTiO3$:Mn4+
with temperature. 相似文献
10.
By means of an improved ligand-field theory, the “pure electronic” PS and
the PS due to EPI of R line of
MgO:V2+ have been calculated,
respectively. The calculated results are in very good agreement with the
experimental data. The behaviors of the pure electronic PS of R line of
MgO:V2+ and the PS of its R line due to EPI are different. It is the
combined effect of them that gives rise to the total PS of R line, which has
satisfactorily explained the experimental results. The mixing-degree of
|t22(3T1)e4T2〉and
|t23 2E〉 in the wavefunction of R level and its variation with
pressure have been calculated and analyzed. The comparison between the
feature of R-line PS of
MgO:V2+ and that of
MgO:Cr3+ has been
made. 相似文献
11.
Traditional ligand-field theory has to be improved by taking into account
both “pure electronic” contribution and electron-phonon interaction one
(including lattice-vibrational relaxation energy). By means of improved
ligand-field theory, R1,
R2, R3',
R2', and R1'
lines, U band, ground-state zero-field-splitting (GSZFS), and ground-state g factors of ruby and/or
GSGG:Cr3+ as well as thermal shifts of GSZFS, R1 line and R2 line of ruby have been calculated. The results are
in very good agreement with the experimental data. Moreover, it is found
that the value of cubic-field parameter given by traditional ligand-field
theory is inappropriately large. For thermal shifts of GSZFS, R1 line and R2 line of ruby, several conclusions have also been obtained. 相似文献
12.
Under various uniaxial stresses, both strains with low symmetry and isotropic strains of crystals take place. The former gives the strain-induced low-symmetry crystal fields and accordingly
splittings of levels; the latter gives the isotropic parts of strain-induced crystal fields and accordingly shifts of levels. By using the wavefunctions obtained from the diagonalization
of the complete d^3$ energy matrix in a regular octahedral field,
the relevant matrix elements and accordingly strain-induced splittings
and/or shifts of t232E and t234A2 for MgO:Cr3+ have been calculated. Their physical
origins have been thoroughly analyzed and revealed. It is the admixtures of basic wavefunctions resulted from the spin-orbit interaction and/or Coulomb interaction and/or Kramers degeneracy
that make strain-induced splittings of levels nonzero. In contrast with this, strain-induced shifts come mainly from the zero-order approximate wavefunctions. It is found that there are nonvanishing matrix elements of operators T2ξ, T2η and T2ζ
between wavefunctions with positive Ms and those with
negative Ms', which have important effects on strain-induced splittings of levels. The shifts of
t232E
under both hydrostatic pressure and uniaxial pressure have been uniformly calculated. The important results of Yc, Zc, Pc, Qc and
〈t2|| C(A1)||
t2〉have been evaluated. 相似文献
13.
The unified theoretical calculation of thermal shifts (TS) of R1 and R2 lines and thermal broadenings (TB) of R, R' and B lines for ruby was carried out for the first time.The calculated results are in very good agr&ment with a great number of experimental data. Especially, by using quantum theory and taking into account all the admixtures of wavefunctions within d3 electronic configuration, all the TM in electron-phonon interaction (EPI), the electronic energy spectrum and lattice-vibration Spectrum, the very important contributions to TS and TB from single-phonon direct process were theoretically calculated in detail. The microscopic essentials of various contributions are revealed, and the mistakes in previous work are remedied. 相似文献
14.
By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of basic wavefunctions within d^3 electronic configuration,the values of all the parameters in the expressions of thermal shift (TS) and thermal broadening (TB) due to EPI for the ground level,R level and R line of MgO:Cr^3 have microscopically been evaluated;and then,TS and TB of R line and various contributions to them have uniformly been calculated.The results are in very good agreement with the experimental data.It is found that all the three terms of TS due to EPI are red shifts;the Raman term is the largest one,and the optical-branch term and neighbor-level term are important for TS;the contribution to TS from thermal expansion is blue shift,which is also important.The R-line TS of MgO:Cr^3 comes from the first-order term of EPI.The elastic Raman scattering of acoustic phonons plays a dominant role in R-line TB of MgO:Cr^3 .For both TS and TB,it is very important to take into account all the admixtures of basic wavefunctions within d^3 electronic configuration. 相似文献
15.
For deuteron's electromagnetic form factors, perturbative QCD (pQCD) predicts that G00+ becomes the dominate helicity amplitude and G+0+ and G+ -+ are suppressed by factors AQCD/Q and AQCD2/Q2 at large Q2 respectively. We try to discuss the higher-order corrections beyond the pQCD asymptotic predictions by interpolating an analytical form to the intermediate energy region. From fitting the data, our results show that the helicity-zero to zero matrix element G00+ dominates the gross structure function A(Q2) in both the large and intermediate energy regions. It is a good approximation for G+ -+ to ignore the higher-order contributions and the higher-order corrections to G+0+ should be taken into account due to sizeable contributions in the intermediate energy region. 相似文献
16.
采用高温固相法制备了SrZn2(PO4)2:Sn2+(SZ2P:Sn2+), SrZn2(PO4)2:Mn2+(SZ2P:Mn2+), SrZn2 (PO4)2:Sn2+, Mn2+(SZ2P:Sn2+, Mn2+) 荧光粉. 通过X射线衍射、激发和发射光谱详细研究了荧光粉的物相和发光性质. 在SrZn2(PO4)2 基质中, Sn2+离子发射光谱是峰值位于461 nm宽带谱, 归属于Sn2+离子的3P1→1S0能级跃迁, SZ2P:Mn2+激发光谱由基质吸收带(200–300 nm)和位于352, 373, 419, 431和466 nm的一系列激发峰组成, 分别对应Mn2+离子的6A1(6S)→4E(4D), 6A1(6S)→4T2(4D), 6A1(6S)→[4A1(4G), 4E(4G)], 6A1(6S)→4T2(4G)和6A1(6S)→4T1(4G)能级跃迁, 因此, SZ2P:Sn2+ 的发射光谱与SZ2P:Mn2+的激发光谱有较大范围的重叠. 结果表明Sn2+对Mn2+发光有明显的敏化作用. 基于Dexter电多极相互作用能量传递公式和Reisfeld近似原理分析, 荧光粉SZ2P:Sn2+, Mn2+中Sn2+-Mn2+离子之间的能量传递机理属于电四极-电四极相互作用引起的共振能量传递, 并计算出Sn2+-Mn2+离子之间能量传递临界距离Rc ≈ 1.78 nm. 通过改变Sn2+, Mn2+离子掺杂浓度, 实现了荧光粉发光颜色的调节, 在254 nm短波紫外激发下荧光粉发出较强的蓝白光. 研究结果表明SZ2P:Sn2+, Mn2+荧光粉有望应用于紧凑型节能灯照明领域, 随着半导体紫外芯片技术的发展, 有潜力应用于未来的白光发光二极管照明领域. 相似文献
17.
《Radiation measurements》2004,38(4-6):579-584
We present photoluminescence spectra of La2.7Lu2.29Cr0.01Ga3O12 and La2.32Lu2.59Cr0.02Ga3.07O12 doped with Cr3+ obtained at high hydrostatic pressure up to 220 kbar, applied in a diamond anvil cell at 20 K and room temperature. In both materials we have obtained a pressure-induced 4T2–2E electronic cross-over. On the basis of the low-temperature R line luminescence at pressures above 100 kbar we have distinguished two dominant Cr3+ sites: and β, existing in both materials, and one minor site δ, that exists only in La2.32Lu2.59Cr0.02Ga3.07O12. The pressure-induced shifts of the R1, R1β and R1δ lines as well as the pressure shift of the broad band related to the 4T2→4A2 transition in both materials have been estimated. 相似文献
18.
CuTe,Cu2和Cu2Te的结构与势能函数 总被引:1,自引:1,他引:0
在Cu和Te的RECP(Relativistic Effective Core Potential)近似下,运用B3LYP方法,在LANL2DZ基组水平上对CuTe,Cu2和Cu2Te分子体系的结构进行优化计算.结果表明,CuTe和Cu2分子的基电子状态分别为2Π和1∑g+,Cu2Te分子的基态为单重态的C2V构型,其电子状态为1A1.同时还计算了Cu2Te分子基态的离解能、力常数和振动频率.采用最小二乘法拟合出CuTe和Cu2分子Murrell-Sorbie势能函数参数.在此基础上,运用多体展式理论方法导出Cu2Te分子基态势能函数的解析表达式,其势能面准确复现了平衡态的结构特征. 相似文献
19.
用高温固相法制备了长余辉发光材料Mg2SiO4:Dy3+,Mn2+,对这种材料的红色长余辉性质进行了研究.对以不同掺杂浓度单掺杂Mn2+、单掺杂Dy3+以及双掺杂Dy3+,Mn2+的Mg2SiO4体系,通过在紫外激发下的发射光谱及其激发光谱的研究,确认了在双掺杂体系中,峰值为660nm的发光带对应着Mn2+的4T1(4G)→6A1(6S)跃迁,Mn2+为主要发光中心.Mn2+的660nm发射的激发谱分布很宽,样品在近紫外和可见光区都有良好的吸收,长波边可达600nm,是这种材料的一个显著优点.还研究了双掺杂体系中Dy3+对Mn2+的660nm发光带的敏化作用.另外,通过对单掺杂、双掺杂体系热释光曲线的比较,揭示了双掺杂体系中Dy3+的陷阱作用. 相似文献
20.
MADong-Ping ZHANGJi-Ping 《理论物理通讯》2001,35(5):627-634
By using the wavefunctions obtained from diagonalizing the complete d^3 energy matrix at normal and various pressures,the g factor of the ground state of SrTiO3:Cr^3 and its pressure-induced shift have been microscopically calculated.Only by taking the local strains around Cr^3 in SrTiO3:Cr^3 (which are about twice the bulk ones)and corresponding P-χ dependence,can we obtain a good agreement etween the calculated result of pressure-induced shift of ground-state g factor and the experimental one.The physical origins of this pressure-induced shift have been explained.It is found that the change of Dq^-1 with pressure makes main contribution to the pressure-induced shift of ground-state g factor of SrTiO3:Cr^3 .By using the wavefunctions obtained from diagonalizing the complete d^3 energy matrix at normal pressure,the relevant matrix elements and accordingly strain-induced splittings of t2^32E and t2^34A2 of SrTiO3:Cr^3 have been calculated.The important results of Yc.Zc,Pc and Qc have also been evaluated.It is the admixtures of basic wavefunctions resulted from the spin-orbit interaction and /or Coulomb interaction and /or Kramers degeneracy that make the strain-induced splittings of the levels nonzero.It is found that there are nonvanishing matrix elements of operators T2ξ between wavefuncgtions with positive Ms and those with negative Ms′ and those with negative ms′,which have important effects on the strain-induced splittings of the levels. 相似文献