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1.
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
2.
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
3.
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
4.
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
5.
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
6.
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
7.
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 wavefunctions within d3 electronic configuration, the thermal shifts (TS) of the ground-state zero-field-splitting (GSZFS) due to EPI for
ruby have microscopic-theoretically been calculated; the contribution
to TS of GSZFS from thermal expansion has also been calculated. The results are in very good agreement with experiments. It is found that the contributions from the first-order perturbation of the second-order term in EPI Hamiltonian are dominant in the
Raman term and optical-branch term for TS of GSZFS; the different between the TS due to EPI of
t23
4A2±(1/2)
e2 (G2) level and the TS due to EPI of
t23
4A2±(3/2)
e2 (G1) level
gives rise to the TS due to EPI of GSZFS, which is very small in
comparison with the TS due to EPI of
G2 or G1 level.
Among various terms in TS of GSZFS, Raman term is the largest one and the signs of the Raman term and optical-branch term are opposite to the sign of the thermal-expansion term; the optical-branch term plays an important role in TS of GSZFS and increases rapidly with temperature; all various contributions
to TS of GSZFS have to be taken into account, since the subtle balance among them determines the total result. The comparison between the features of TS of GSZFS and those of TS of
R1 and R2 lines has been made. For TS of GSZFS, the contribution from thermal expansion is especially important; the neighbor-level term is insignificant. 相似文献
8.
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
9.
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
10.
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
11.
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
12.
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
13.
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
14.
从能量传递的角度出发,利用同步辐射光源(德国HASYLAB实验室的SUPERLUMI实验站)对Pr3+和Mn2+掺杂的SrB4O7粉末样品进行了光谱研究.206nm激发下,在SrB4O7:Pr3+(0.1%,摩尔分数)样品中观察到了来自Pr3+离子1S0能级的光子级联发射.SrB4O7:Pr3+样品的发射谱与SrB4O7:Mn2+样品监测Mn2+离子640nm发射的激发谱在330~430nm的波长范围里存在显著的光谱重叠.这个光谱重叠有利于Pr3+→Mn2+的能量传递发生,从而将Pr3+离子级联发射中第一步不实用的紫外或近紫外光子转换为Mn2+的红光发射.双掺杂样品SrB4O7:Pr3+,Mn2+与单掺杂样品SrB4O7:Pr3+的发射谱比较揭示出Pr3+→Mn2+的能量传递的确存在,并且提供了一种传递效率的估算方法,表明通过“Pr3+-Mn2+”组合有可能获得量子效率大于1的高效真空紫外激发发光材料. 相似文献
15.
用高温固相法合成了红色长余辉发光材料LiAl5O8:Mn4+,Li5AlO4:Mn4+,LiAlO2:Mn4+,发现前两种材料有红色余辉,这方面并没有报道过,并对这两种材料的发光性能作了研究,指明了不同基质中发光强弱不同原因。对不同Mn4+掺杂浓度的材料做了浓度依赖关系研究,确认Mn4+的发光是2E→4A2的跃迁。Mn4+的发光是个宽带谱,材料在紫外区有强的吸收,发射谱范围可达620~770nm,峰值在675nm。对长余辉机制进行了探讨。 相似文献
16.
By diagonalizing the complete d3 energy matrix in a trigonally distorted cubicfield and using the wavefunctions from it, unified calculations of the whole energy spectrum as well as the g factors of the ground state and t23 2 E excited states for α-A1203:Cr3+ and α-A1203:Mn4+ have been carried out respectively. A11 the calculated results are in very good agreement with the experimental data. The comparison between the results of the two crystals has been made, which demonstrates that the covalency of α-A1203:Mn4+ is stronger than the one of α-A1203:Cr3+. For the zero-field splittings of the ground state and t23 2 E , their physical origins are revealed; the comparison and analysis of their values of the two crystals have been made. 相似文献
17.
采用高温固相法制备了颜色可调的NaTaOGeO4∶Tb3+,Mn2+荧光粉,并研究了其发光特性以及能量传递机理。在244 nm激发下,NaTaOGeO4∶Tb3+的发射光谱的发射峰分别位于380,413,436,492,544 nm,分别属于Tb3+的5D3→7FJ和5D4→7FJ(J=6,5,4)能级跃迁,为蓝光和绿光发射。在280 nm波长激发下,在492 nm和544 nm处有较强的发射峰,分别属于Tb3+的5D4→7F6、5D4→7F5能级跃迁,为绿光发射。在248 nm波长激发下,NaTaOGeO4∶Mn2+的发射光谱由位于576 nm处的宽带组成,属于Mn2+的4T1→6A1能级跃迁。当在NaTaOGeO4∶Tb3+荧光粉中共掺杂Mn2+时,可以同时观察到Mn2+和Tb3+的发射峰,通过改变浓度掺杂比,可以得到颜色可调控的荧光粉。 相似文献
18.
利用高温固相法制备了Ba9Y2(SiO4)6:Ce3+,Mn2+(BYS:Ce3+,Mn2+)荧光粉,并通过X射线衍射(XRD)谱、激发和发射光谱及荧光寿命的测试对材料的结构、发光特性和能量传递进行了研究。在327 nm激发下,BYS:Ce3+,Mn2+发射光谱中包含2个发射峰,分别为位于407 nm的Ce3+的蓝紫光发射和位于597 nm的Mn2+的红光发射。在该体系中,发现了Ce3+向Mn2+的有效能量传递,使得Mn2+在597 nm处的红光发射显著提高,当x(Mn2+)=0.25时,BYS:Ce3+,xMn2+的能量传递效率可达39%。实验表明,该荧光粉可为紫外基白光LED提供良好的红光光源。 相似文献
19.
S. P. Feofilov A. A. Kaplyanskii A. B. Kulinkin R. S. Meltzer T. N. Vasilevskaya 《Journal of luminescence》2002,100(1-4):155-161
We report optical studies of the new material – Cr3+-doped lithium–germanate glass, containing Li2Ge7O15 (LGO) nanocrystalline particles. While only broadband 4T2–4A2 fluorescence from the low-field octahedral Cr3+ sites was observed from Cr3+ ions in the glass, in LGO nanocrystals high-field Cr3+ centers emit 2E–4A2 (R–lines) fluorescence. The process of crystallization in the course of isothermal annealing of glasses was monitored spectroscopically and the nucleation of LGO crystallites was observed starting from the smallest clusters. Using the 2E–4A2 fluorescence spectra it is possible to detect the ferroelectric phase transition in LGO:Cr3+ nanocrystals, whose critical temperature was found to be similar to that of the bulk crystals. Long-lived spectral holes were burned in the inhomogeneously broadened R-lines of Cr3+ in LGO nanocrystals at low temperatures. The linear temperature dependence of hole widths shows that the homogeneous broadening of 4A2–2E transitions of Cr3+ in nanocrystals is due to interaction of Cr3+ electronic levels with the two-level systems (TLS) of the surrounding glass. The range of the Cr3+-TLS elastic dipole–dipole interaction is estimated. 相似文献