The optical absorption and emission spectra of Cs2NaSmCl6

Optical absorption and emission spectra are reported for single crystals of the cubic elpasolite Cs₂NaSmCl₆. The variable temperature spectra obtained at high resolution are assigned using energies and relative intensities. Transitions from the ground level, ⁶H_{$\text{5}\text{2}$} to cystal fi levels of ⁶H_{$\text{7}\text{2}$-$\text{15}\text{2}$}, ⁶F_{$\text{1}\text{2}$-$\text{11}\text{2}$}, ⁴G_{$\text{5}\text{2}$-$\text{9}\text{2}$}, ⁴F_{$\text{3}\text{2}$,$\text{5}\text{2}$}, ⁴I_{$\text{9}\text{2}$}, and ⁶P_{$\text{3}\text{2}$, $\text{5}\text{2}$} are located and characterized. Intensity calculations are reported for magnetic dipole allowed transitions. The dominance of vibronic intensity in ⁶H_{$\text{5}\text{2}$}→⁶F _{$\text{1}\text{2}$-$\text{9}\text{2}$} and ⁶P_{$\text{3}\text{2}$, $\text{5}\text{2}$} transitions is accounted for qualitatively through the ligand polarization model involving quadrupole metal (Sm³⁺)-ligand (Cl^?) interaction mechanisms. The E_u″(⁶H_{$\text{5}\text{2}$})→E′(⁶H_{$\text{1}\text{2}$}) E_u′(⁶F_{$\text{1}\text{2}$}) no-phonon transition is postulated to be pure electric quadrupole allowed. The ground state magnetic moment is determined to be very small from magnetic circular dichroism (MCD) spectra.This study has led to the assignment of nearly all of the crystal field levels in the visible and IR region for Cs₂NaSmCl₆. A total of 27 such levels were identified, 17 from no-phonon transitions and the rest from vibronic transitions. The magnetic dipole intensity calculated using intermediate coupling O_h wavefunctions along with a crystal field analysis of the splitting pattern was used in the assignment of the levels. Vibronic bands were observed for all transitions and their vibrational symmetries were tentatively assigned. MCD data were used to determine the magnet moment of the ground state.     

Emission spectra of Cs2NaTbCl6 and Cs2NaYCl6: Tb3+

The emission spectra of microcrystalline Cs₂NaTbCl₆ and Cs₂Na(Y_0.99Tb_0.01)Cl₆ have been measured at room temperature and at 77 K. The crystal structures of these compounds are face-centered cubic and the terbium (III) ions lie at sites of octahedral (O_h) symmetry surrounded by six chloride ions. Emission is observed from both the ⁵D₃ and ⁵D₄ excited states of Tb³⁺. Assignments have been made for nearly all of the magnetic-dipole transitions split out of the Tb³⁺⁷F₆, ⁷F₅, ⁷F₄, ⁷F₃, ⁷F₂, ⁷F₁ ← ⁵D₄ and ⁷F₄, ⁷F₂ ← ⁵D₃ transitions. These assignments are based on the calculated transition energies and relative magnetic-dipole strengths and intensities obtained from a weak-field crystal-field analysis of octahedral TbCl₆^3? units. Magnetic-dipole lines dominate the spectra for transitions of ΔJ = ±1 free-ion parentage, whereas both magnetic-dipole lines and vibronically induced electric-dipole lines contribute significantly to the emission intensities of the ΔJ = 0, ±2 transitions. The crystal-field sub-levels of both ⁵D₃ and ⁵D₄ appear to reach a Boltzmann thermal equilibrium prior to emission. Emission from ⁵D₃ is partially quenched in going from low temperature to high temperature and in going from Cs₂NaYCl₆: Tb³⁺ (1%) to Cs₂NaTbCl₆.This study has led to the identification and assignment of nearly all of the pure magnetic-dipole transitions split out of the Tb³⁺⁷F₆, ⁷F₅, ⁷F₄, ⁷F₃, ⁷F₂, ⁷F₁ ← ⁵D₄ and ⁷F₄, ⁷F₂ ← ⁵D₃ transitions in crystal-line Cs₂NaTbCl₆. The assignments were based on calculated transition energies and relative magnetic-dipole strengths (and intensities) obtained from a (weak-field) crystal-field analysis of octahedral (O_h) TbCl₆^3? clusters. Excellent agreement between the calculated and observed relative intensities of the magnetic-dipole lines was achieved by assuming a Boltzmann equilibrated set of crystal-field sub-levels for both the ⁵D₄ and ⁵D₃ emitting states. Furthermore, the experimental results suggest that ⁵D₄ ← ⁵D₃ relaxation is temperature-dependent.The energy levels calculated and displayed in table 1 appear to be qualitatively correct and are in semiquantitative agreement with the emission results (as interpreted in section 4). Calculated and observed transition energies for the assigned magnetic-dipole transitions generally agree to within 0.2%.One of the most remarkable features of the emission spectra obtained on Cs₂NaTbCl₆ is the absence of any vibrational structure in the ΔJ = ± 1 transitions (⁷F₆, ⁷F₃ ← ⁵D₄ and ⁷F₄, ⁷F₂ ← ⁵D₃), and the presence of extensive vibrational structure in the ΔJ = O, ±2 transitions (⁷F₆, ⁷F₄, ⁷F₂ ← ⁵D₄). If other than OO vibronic transitions do contribute to the ΔJ = ±1 emissions, their intensities must be at least two or three orders-of-magnitude weaker than the OO magnetic-dipole lines. Vibronically induced electric-dipole transitions appear, however, to make substantial contributions to the ⁷F₆, ⁷F₄, ⁷F₂ ← ⁵D₄ emission spectra. A clear-cut theoretical explanation for the absence of vibrational structure in the ΔJ = ±1 transitions is not readily apparent. We are presently examining this problem in greater detail.     

Luminescence and crystal growth of Cs2NaYCl6Bi

The crystal growth of Cs₂NaYCl₆ doped with Bi³⁺ is described and its luminescence properties reported and discussed.     

The luminescence of Cs3Bi2Cl9 and Cs3Sb2Cl9

The luminescence properties of Cs₃Bi₂Cl₉, α-Cs₃Sb₂Cl₉, and β-Cs₃Sb₂Cl₉ are reported and compared with those of Cs₃Bi₂Br₉. The first two compounds have comparable luminescence properties which can be described in terms of a band model. Deep center emission is observed for both compounds, whereas edge emission is observed only for Cs₃Bi₂Cl₉. The optical transitions of β-Cs₃Sb₂Cl₉ are localized on the Sb³⁺ ion. The orientation of the lone-pair orbitals of the ns² ions seems to play an important role in the formation of the cationic valence band. The α-β transformation must therefore have a considerable influence on the spectral properties of Cs₃Sb₂Cl₉.     

Phase transitions in a Cs2−xK1+xBiCl6 solid solution

A solid solution with a Cs_2?xK_1+xBiCl₆ (0 ≤ x ≤ 1) formulation and an elpasolite-related structure was prepared. At room temperature the symmetry is cubic (Fm3m) for x = 0 and triclinic $\text{(P}\text{I}\text{)}$ for x ≠ 0. For 0 ≤ x ≤ 1, various techniques enabled us to detect a phase transition of the ferroelastic-paraelastic type at t_c (°C) temperature. The t_c and ΔH_tc values are correlated to the size of the alkali ions.     

Syntheses, structures, optical properties, and theoretical calculations of Cs2Bi2ZnS5, Cs2Bi2CdS5, and Cs2Bi2MnS5

Three new compounds, Cs₂Bi₂ZnS₅, Cs₂Bi₂CdS₅, and Cs₂Bi₂MnS₅, have been synthesized from the respective elements and a reactive flux Cs₂S₃ at 973 K. The compounds are isostructural and crystallize in a new structure type in space group Pnma of the orthorhombic system with four formula units in cells of dimensions at 153 K of a=15.763(3), b=4.0965(9), c=18.197(4) Å, V=1175.0(4) Å³ for Cs₂Bi₂ZnS₅; a=15.817(2), b=4.1782(6), c=18.473(3)  Å, V=1220.8(3)  ų for Cs₂Bi₂CdS₅; and a=15.830(2), b=4.1515(5), c=18.372(2) Å, V=1207.4(2) Å³ for Cs₂Bi₂MnS₅. The structure is composed of two-dimensional _∞²[Bi₂MS₅²⁻] (M=Zn, Cd, Mn) layers that stack perpendicular to the [100] axis and are separated by Cs⁺ cations. The layers consist of edge-sharing _∞¹[Bi₂S₆⁶⁻] and _∞¹[MS₃⁴⁻] chains built from BiS₆ octahedral and MS₄ tetrahedral units. Two crystallographically unique Cs atoms are coordinated to S atoms in octahedral and monocapped trigonal prismatic environments. The structure of Cs₂Bi₂MS₅, is related to that of Na₂ZrCu₂S₄ and those of the AMM′Q₃ materials (A=alkali metal, M=rare-earth or Group 4 element, M′= Group 11 or 12 element, Q=chalcogen). First-principles theoretical calculations indicate that Cs₂Bi₂ZnS₅ and Cs₂Bi₂CdS₅ are semiconductors with indirect band gaps of 1.85 and 1.75 eV, respectively. The experimental band gap for Cs₂Bi₂CdS₅ is ≈1.7 eV, as derived from its optical absorption spectrum.     

Laser-induced infrared fluorescence of Cs2

Fluorescence induced by several exciting lines from an argon-ion laser has been recorded by high-resolution Fourier-transform spectrometry in the 4000-     

K+掺杂双钙钛矿Cs2AgInCl6的发光性质

采用固相球磨法制备了K⁺掺杂双钙钛矿Cs₂AgInCl₆纳米材料,该方法无需配体辅助,绿色环保。通过X射线衍射谱和拉曼光谱对晶体结构进行研究,通过激发光谱、发射光谱和时间分辨光谱对其发光性能进行研究。结果表明,Cs₂AgInCl₆为立方晶体,属于Fm3m空间群,由于宇称禁戒跃迁,其荧光量子产率(PLQY)低,小于0.1%。低于60%的K⁺掺杂主要取代Ag⁺的位置,引起Cs₂AgInCl₆的晶格膨胀,消除了晶格结构的反演对称性,打破了宇称禁戒跃迁,掺杂后Cs₂AgInCl₆的光致发光强度显著增强。K⁺的最佳掺杂比例为40%,Cs₂Ag_0.6K_0.4InCl₆发出中心波长为640 nm,半高宽为180 nm,平均荧光寿命达到29.2 ns,PLQY达到10.5%。当K⁺掺杂比例超过60%,K⁺开始取代Cs⁺的位置,产物发生相变,出现立方相的Cs_2-xK_1+x-yAg_yInCl₆和单斜相的Cs_2-xK_1+xInCl₆产物,这些产物由于强电子-声子耦合,非辐射复合占据主导地位。     

Dual interfacial engineering for efficient Cs2AgBiBr6 based solar cells

The emerging lead-free halide double perovskite solar cells have attracted widespread attentions due to their long-term stability and non-toxicity, but suffer from the low device performance. One efficiencylimiting factor is the improper contacts between the halide double perovskite and anode/cathode electrodes. Here, we improve the efficiency and stability of the bismuth-halide double perovskite based solar cells by a synergistic interface design for both electron and hole transport layers(ETL/HTL). The results show that the modification of the TiO_2 ETL with a thin hydrophobic C60 layer and replacement of the lithium-doped small molecule HTL with an un-doped conjugated polymer lead to higher surface quality of perovskite film and better energy-level alignment at the contacts. As a result, the optimized device shows reduced trap density, suppressed charge recombination and enhanced charge extraction, leading to an increase of 69% in device efficiency. In addition, the device also exhibits superior stability in ambient environment, heat stress and light bias after interface optimization. This work provides an efficient strategy for the device optimization of the emerging lead-free perovskite solar cells.     

Phase transition in ZnGeF6 · 6H2O

In ZnGeF₆·6H₂O crystal (containing Mn(II) in the ratio of Zn(II) to Mn(II) 100:1 and 10:1) a phase transition connected with the occupation of two inequivalent octahedra complexes GeF^2?₆ positions was discovered and studied by means of ESR. The phase transition has a hysteresis nature. Transition temperature ranges depend on the concentration of the added ion. The origins of these phenomena are discussed.     

On the crystal field of Cs2NaY0.99Eu0.01Cl6

Crystal field parameter for cubic Cs₂NaEu_xY_1?xCl₆ (with x = 0.01) are reported. The values are A⁰₄ = 225 cm^?1 and A⁰₆ = 15 cm^?1.     

Phase formation in Cs2MoO4-MMoO4-Zr(MoO4)2 (M = Mn, Mg, Co, Zn) systems and crystal structure of new double molybdates Cs2MnZr2(MoO4)6 and Cs2MnZr(MoO4)4

Subsolidus phase relations in the Cs₂MoO₄-MMoO₄-Zr(MoO₄)₂ (M = Mn, Zn) ternary systems were determined, and two groups of new isostructural triple molybdates were synthesized: Cs₂MZr(MoO₄)₄ and Cs₂MZr₂(MoO₄)₆ (M = Mn, Mg, Co, Zn). Cs₂MnZr₂(MoO₄)₆ and Cs₂MnZr(MoO₄)₄ crystals were grown by spontaneous flux crystallization and used in structure solution for both groups of compounds. The Cs₂MnZr₂(MoO₄)₆ structure (a =13.4322(2) ?, c = 12.2016(3) ?, group R3, Z = 3, R = 0.0367) is a new structure type characterized by a mixed three-dimensional framework built of corner-sharing MoO₄ tetrahedra and (M, Zr)O₆ octahedra where large channels are occupied by cesium cations. Cs₂MnZr₂(MoO₄)₄ (a =5.3890(1) ?, c = 8.0685(3) ?, space group P $ \bar 3 $ \bar 3 m1, Z = 0.5, R = 0.0247) has the layered glaserite-like KAl(MoO₄)₂ type structure, where Al³⁺ octahedral positions are randomly occupied by a 0.5M²⁺ + 0.5Zr⁴⁺ mixture.     

Magnetic circular dichroism of the A2 → E(D) transition in Cs3CoCl5

MCD measurements have been used to estimate the ground- and excited-state magnetic moments and zero-field splittings for the ⁴A₂ → ²E(²D) transition in Cs₃CoCl₅.     

K+掺杂双钙钛矿Cs2AgInCl6的发光性质

采用固相球磨法制备了K⁺掺杂双钙钛矿Cs₂AgInCl₆纳米材料,该方法无需配体辅助,绿色环保。通过X射线衍射和拉曼光谱对晶体结构进行研究,通过激发光谱、发射光谱和时间分辨光谱对其发光性能进行研究。结果表明,Cs₂AgInCl₆为立方晶体,属于Fm3m空间群,由于宇称禁戒跃迁,其荧光量子产率(PLQY)低,小于0.1%。低于60%的K⁺掺杂主要取代Ag⁺的位置,引起Cs₂AgInCl₆的晶格膨胀,消除了晶格结构的反演对称性,打破了宇称禁戒跃迁,掺杂后Cs₂AgInCl₆的光致发光强度显著增强。K⁺的最佳掺杂比例为40%,Cs₂Ag_0.6K_0.4InCl₆材料发射中心波长为640 nm,半高宽为180 nm,平均荧光寿命达到29.2 ns,PLQY达到10.5%。当K⁺掺杂比例超过60%,K⁺开始取代Cs⁺的位置,产物发生相变,出现立方相的Cs_2-xK_1+x-yAg_yInCl₆和单斜相的Cs_2-xK_1+xInCl₆产物,这些产物由于强电子-声子耦合,非辐射复合占据主导地位。     

Phase Transition in Cs2KMnF6: Crystal Structures of Low- and High-Temperature Modifications

Crystalline Cs₂KMnF₆, when prepared below 500°C, adopts a tetragonal elpasolite structure type. Differential scanning calorimetric investigations indicated that Cs₂KMnF₆ undergoes a phase transition from the low-temperature tetragonal phase (LT) to a high-temperature phase (HT) at about 530°C. Single crystals of the new HT phase could be obtained by annealing a crystalline LT specimen at 600°C followed by rapid quenching to room temperature. In the present study the structures of both phases have been studied by single-crystal X-ray diffraction techniques. The LT phase has the tetragonal space group symmetry I4/mmm, with unit-cell parameters a=6.319(1) (a· =8.936) and c=9.257(2) Å, and Z=2. The HT phase has the cubic symmetry Fm3m, with the cell parameter a=9.067 Å and Z=4. Structural models of the LT and HT phases have been refined vs collected single-crystal X-ray reflection data to R values of 0.034 and 0.022, respectively. The uneven Mn–F bond distance distribution in the LT form, four bonds of 1.860(6) two of 2.034(9) Å, are typical for an octahedrally coordinated high-spin Mn³⁺ ion affected by Jahn–Teller effects. Due to symmetry constraints, all six octahedral Mn–F bonds in the HT form are equal to 1.931(5) Å. However, the mean square atomic displacement parameters of the fluorine atoms increases significantly from about 0.022 Ų for the LT phase to 0.042 Ų for the HT phase. The increased displacement parameters indicate that the phase transition from the LT to the HT form is associated with a directional disorder of the Jahn–Teller distortions around the Mn³⁺ ions.     

A possible transition state for the H2 + D2 exchange reaction

A proposal for a possible transition state for the H₂ + D₂ exchange reaction follows from an analysis of the Jahn-Teller instability of tetrahedral H₄. The suggested pathway involves pseudo-rotation in the e deformation space, with a compressed tetrahedral structure corresponding to the reaction saddle point.     

Syntesis and Crystal Structure of Cs2Nb6Br5F12: A Nb6 Cluster Compound with a One-Dimensional Nb6Br5F7F6 Unit Connection

The synthesis and the crystal structure of Cs₂Nb₆Br₅F₁₂ containing octahedral niobium clusters are presented in this work. This bromofluoride is based on a Nb₆Lⁱ₁₂F^a₆ (L=Br and F) unit and crystallizes in the orthorhombic system (space group, Cccm; Z=4; a=9.2446(2) Å, b=13.6256(3) Å, and c=17.1665(4) Å; R=0.0241). Fluorine and bromine are randomly distributed on the inner ligand positions, Lⁱ, that edge-bridge the Nb₆ cluster whereas fluorine fully occupies the apical positions (L^a). The units are linked to each other by apical ligands leading to an original one-dimensional unit connection. The cesium atoms are statistically distributed on several sites that describe parallel channels along the [1 0 0] direction. The influence of fluorine ligands upon the stabilization of this structure type as well as the structural relationships with Ba₂Zr₆Cl₁₇(B), Nb₆F₁₅, and NaMo₆Cl₁₃ will be evidenced and discussed.     

Infrared absorption and magnetic circular dichroism of Cs2ZrCl6:Ir4+

The E″_g(²T_2g) å U′_g(²T_2g) transition of Ir⁴⁺ in Cs₂ZrCl₆ is observed in the infrared energy range 5000–6000 cm^?1 by absorption and magnetic circular dichroism spectroscopy. The resolved vibrational structure provides detailed information about the change in vibrational frequencies on excitation and the transition intensity mechanism. The energy of the transition requires the Ir⁴⁺ spin-orbit coupling parameter ζ to be ≈ 2800 cm^?1.     

Crystal chemistry peculiarities of Cs2Te4O12

The Raman and IR-absorption spectra of the Cs₂Te₄O₁₂ lattice are first recorded and interpreted. Extraordinary features observed in the structure and Raman spectra of Cs₂Te₄O₁₂ are analyzed by using ab initio and lattice-dynamical model calculations. This compound is specified as a caesium-tellurium tellurate Cs₂Te^IV(Te^VIO₄)₃ in which Te^IV atoms transfer their 5p electrons to [Te^VIO₄]₃⁶⁻ tellurate anions, thus fulfilling (jointly with Cs atoms) the role of cations. The Te^VI-O-Te^VI bridge vibration Raman intensity is found abnormally weak, which is reproduced by model treatment including the Cs⁺ ion polarizability properties in consideration.     

The crystal structure of “green” Cs2[VOF4(H2O)] and its relationship to “blue” Cs2[VOF4(H2O)]

Crystals of a second, “green” modification of Cs₂[VOF₄(H₂O)] were obtained from aqueous solution. Their crystal structure was studied on the basis of three-dimensional X-ray data. The structure is orthorhombic, a = 8.231(3), b = 10.323(3), c = 8.497(3) Å, V = 722.0ų, Z = 4, space group Ccmm. The final R and R_W were 0.035 and 0.048, respectively, for 421 independent reflections. As the already known “blue” modification, the present structure contains isolated, highly deformed octahedral [VOF₄(H₂O)]^2? ions with the oxygen atoms in trans positions. The cesium sublattice and the orientation of the anions to each other are completely different in both modifications. uv/VIS reflection, and ir and Raman spectra of both modifications are discussed.