Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
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Halide Perovskite-Derived Compounds Rb2TeX6 (X = Cl, Br, and I): Electronic Structure of the Ground and First Excited States Alexander A. Dotsenko,*,† Vitaliy I. Vovna,† Vladimir V. Korochentsev,† Anatoliy G. Mirochnik,‡ Oleg L. Shcheka,§ Tatyana V. Sedakova,‡ and Valentin I. Sergienko‡ †
Far Eastern Federal University, Vladivostok 690090, Russia Institute of Chemistry, Russian Academy of Sciences, Vladivostok 690022, Russia § Far Eastern State Technical Fisheries University, Vladivostok 690087, Russia
Inorg. Chem. Downloaded from pubs.acs.org by UNIV OF LOUISIANA AT LAFAYETTE on 04/26/19. For personal use only.
‡
S Supporting Information *
ABSTRACT: Herein, we report a study of the electronic structure of the ground and first excited states of Rb2TeCl6, Rb2TeBr6, and Rb2TeI6 halide-perovskite-derived crystals. Using X-ray photoelectron spectroscopy (XPS) measurements and density functional theory and multiconfiguration self-consistent field (MCSCF) calculations, the experimental and theoretical XPS spectra of the valence region were obtained. In addition, the effects of the cations and halogen atoms on the electronic structure were determined, and the classification of the excited states in double point group representation was carried out. Furthermore, a possible reason for the luminescence quenching in an isostructural series of crystals containing the [TeI6]2− anions was determined.
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INTRODUCTION
In this paper, we consider a series of Rb2TeX6 crystals (X = Cl, Br, and I), which are characterized as having covalent− ionic type (predominantly ionic) chemical bonds. The crystals of this material have O5h symmetry and belong to the Fm3m space group.24−26 An image of the unit cell is shown in Figure 1. The Rb2TeX6 crystals are composed of [TeX6]2− anions, each of which is surrounded by eight Rb+ cations in a regular octahedral structure. The structure of centrosymmetric crystals of this type is determined by the relative sizes and charges of the anions, which have an approximately spherical shape. On binding cations, they form structures with densely packed layers. Crystals with [TeCl6]2− and [TeBr6]2− anions have strong luminescent properties,13,17,22,23 whereas those with [TeI6]2− anions show polymorphism and phase transitions.26−28 An interesting feature of these crystals is that the probability of transitions to the excited states depends mainly on the local environment of the s2-ion, i.e. the halogen atom. By doping or substituting some halogen atoms, one can shift the emission spectrum of particles by several nanometers.10 This makes them effective in producing photonic integrated circuits with control over the reversible adjustment of the radiation color of nanoscale sources. However, this requires an understanding of the luminescence mechanism and luminescence quenching.
The search for new materials to ensure the transition to leadfree technology is an important task in modern inorganic chemistry. Following the rules and new standards limiting the use of the lead in the Waste Electrical and Electronic Equipment Directive (WEEE), Restriction of Hazardous Substances Directive (RoHS), and Final Review of Scientific Information on Lead UNEP, most high-tech companies have been forced to abandon traditional lead-containing materials for reasons of energy efficiency, human health, and environmental protection.1−3 These materials include halide-perovskite-derived complexes,4−11 the most promising of which are complexes with the general formula A2BX6 (where A is organic or inorganic cations, B are so-called s2-ions (TiIV, HfIV, ZrIV, PdIV, PbII, SnIV, TeIV, SbIII, and BiIII), and X are halogens (F, Cl, Br, and I)). These compounds possess interesting luminescent, optical, dielectric, and magnetic properties and have applications in modern semiconductor devices.4−15 Currently, these materials are used to increase the power of photovoltaic modules4−16 or increase the luminescence quantum yield.17−23 The extensive scope of applications of this class of compounds makes the study of their electronic structure necessary, including the luminescence process, the relationship between the electronic structure and optical properties, the role of ligand−metal charge transfer, the influence of the Jahn−Teller effect, and the spin−orbit interactions.10−13 © XXXX American Chemical Society
Received: January 26, 2019
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DOI: 10.1021/acs.inorgchem.9b00250 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
Figure 1. Crystal structure of Rb2TeX6 (X = Cl, Br, and I). The calculation of the molecular orbital (MO) energies was performed using the full-electron version of the TZVP basic set without using an ECP according to our previously proposed method.34−39 The calculations of the energies and geometries of the excited states were performed using the multiconfigurational selfconsistent field (MCSCF) CASSCF (8,7) method with the SVP basic set. Details of XPS Measurements. X-ray photoelectron spectra were recorded on an ultrahigh vacuum photoelectron spectrometer (Omicron, Germany). An X-ray tube with a magnesium anode (Mg Kα = 1253.6 eV) was used as the radiation source. The pressure in the chamber during the experiment did not exceed 9 × 10−9 mbar. The value of the emission current (I) was 13 mA and the anode voltage (U) was 10 kV. The instrumental function of the spectrometer used for recording the lines of characteristic atomic energy levels, which was determined from the Ag 3d5/2 line shape, had a full width at half-maximum (fwhm) of 1.2 eV. The portions of the spectra of the characteristic energies of O 1s, C 1s, I 3d, Cl 2p, Br 3p, and Te 3d, as well as those of other atoms, were recorded at an analyzer transmission energy of 20 eV. In the process of accumulating the spectra, the characteristics of the lines did not change. The spectra were processed according to standard procedures using the Casa XPS program.40 The compounds under study were powders applied on a sticky substrate. The neutralization problem was solved by calibrating the electron binding energy scale using the internal standard method, and the C 1s level (285.0 eV) was chosen as a standard. During the experiment, intense luminescence of the samples under study was observed. The spectra were processed by standard procedures. The background was subtracted by the Shirley method.41 The smoothing of the spectra was performed using a Savitsky−Golay (SG) digital smoothing polynomial filter; a quadratic function with an approximation interval length of 13 points was used as an approximating polynomial.42 The interpretation of the valence electron spectra was carried out on the basis of calculations of the electronic structure of crystal fragments using the density functional defects approximation originating from the Koopmans theorem applied to DFT: Ii = −εi + δi (I, ionization energy; εi, MO energy; δi, DFA defect), as proposed in our papers.34−39 Modeling of Theoretical XPS Spectra. The simulation of the theoretical XPS spectra was performed by decomposition into Gaussian functions while considering the hardware function, data for the photoionization cross sections, electron binding energies, and spin−orbit splitting for the resulting atomic orbital (AO) contributions to the MO.43,44 The contributions were calculated using Mulliken population analysis (MPA) and MO decomposition based on the linear combination of AOs.45 In this method, the electron density of an atom is determined as the sum of the squares of the coefficients of the MO decomposition into the AOs of the atom plus half the overlap density of the atomic orbitals with the neighboring atom. The total theoretical XPS spectrum is the sum of Gaussian functions. Each Gaussian function corresponds to a separate
The objective of this manuscript is to present our work devoted to understanding the electronic structure of Rb2TeX6 and the mechanism of luminescence using X-ray photoelectron spectroscopy (XPS) measurements and density functional theory (DFT) and complete active space self-consistent field (CASSCF) calculations. The next section presents the calculation parameters and the fragments used to model the crystal as well as the details of the XPS measurements and the method for modeling the theoretical spectra. In the Results and Discussion, an analysis of the electronic structure is carried out, theoretical and experimental XPS spectra of the valence region are presented, and a description of this region is given. Then, a systematic analysis of the first excited states in the double point group representation is presented. The final section presents the main conclusions.
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EXPERIMENTAL AND THEORETICAL DETAILS
Calculation Parameters. The electronic structure was calculated using the DFT approximation in the FireFly software package with the B3LYP hybrid functional.29,30 To simplify the calculations, analysis, and data processing, only certain fragments of the crystal were considered, as shown in Figure 2.
Figure 2. Structure of Rb2TeX6 crystal fragments with (a) Oh and (b) D3d symmetry.
The lengths of the Te−X bonds of fragment (a) in Figure 2 correspond to the experimental bond lengths for Rb2TeCl6, Rb2TeBr6, and Rb2TeI6 of 2.433, 2.554, and 2.939 Å, respectively; similarly, the lengths of the Rb−X bonds in Rb2TeCl6, Rb2TeBr6, and Rb2TeI6 are 3.628, 3.810, and 4.105 Å, respectively.24−26 For fragment (b), a procedure for optimizing the geometry of the ground state was performed with the experimental bond lengths. The optimization of the ground state geometry using the DFT method was performed using the SVP and TZVP basis sets with effective core potentials (ECP) for the tellurium, rubidium, and iodine atoms.31−33 B
DOI: 10.1021/acs.inorgchem.9b00250 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry molecular orbital. The height of each Gaussian function corresponding to the intensity in the spectrum is defined as the sum of the multiplication of each contribution of the atomic orbitals (for example, Cl 2s, Cl 2p, and Cl 3s) to the MO by the corresponding ionization cross section of the electron shell of a free atom with radiation with energy of 1253.6 eV (Mg Kα). The position of the Gaussian function in the energy scale corresponds to the MO energy. The fwhm is equal to the spectrometer hardware function, i.e. 1.2 eV. The values used for the photoionization cross sections are presented in Table 1. The values of
of the three or two, respectively, MOs is shown. Tables listing the AO contributions to the MOs for Rb2TeX6 and free anions [TeX6]2− are presented in the Supporting Information. The energies, intervals, and sequence of MOs in fragments of the Rb2TeX6 crystal are presented in the correlation diagram (see Figure 4).
Table 1. Photoionization Cross Sections of Free Atoms at Photon Energy 1253.6 eV (Mg Kα) Used in the XPS Experiment43 atom
electron
σ
atom
electron
σ
Cl Cl Br Br Br I I I
3s 3p 4s 3d 4p 5s 4d 5p
3.6 3.3 3.4 67 6.3 2.5 87 5.4
Rb Rb Rb Te Te Te Te Te
4s 3d 4p 3d 4p 5s 4d 5p
4.5 99 12 672 57 2.2 76 3.5
the ionization cross sections are given in relative (to the C 1s cross section) units. The value of spin−orbit splitting taken into account in theoretical Rb 4p XPS was taken from the X-ray Data Booklet;44 it is 1 eV. The MOs corresponding to Rb 4p3/2 were shifted relative to Rb 4p1/2 by the value of the spin−orbit splitting. The total contribution of the Rb 4p MO obtained from the calculated data and used to account for the contribution of the Rb 4p1/2 and Rb 4p3/2 components is proportional to their statistical weights of 1/3 and 2/3, respectively.
Figure 4. Energy diagram of valence MOs for Rb2TeX6 (X= Cl, Br, and I) crystal fragments.
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RESULTS AND DISCUSSION Electronic Structure of Rb2TeX6 in the Ground State. According to the DFT calculations, the electron configuration of the anions in Rb2TeX6 is 1a1g21t1u61eg42a1g22t1u61t2g62eg41t2u63t1u61t1g63a1g24t1u0. The HOMO is the 3a1g MO, and the LUMO is the 4t1u MO. Images of the molecular orbitals are shown in Figure 3 using [TeI6]2− as an example. For the degenerate t and e MOs, one
Because the crystal structure fragment with symmetry Oh has a charge of +6, the binding of the energy scale was performed using the a2g (1t1g) MO of the neutral fragment in D3d symmetry. The optimized bond lengths of the Te−X fragment in D3d symmetry for Rb2TeCl6, Rb2TeBr6, and Rb2TeI6 are 2.584, 2.756, and 3.000 Å, respectively, and the Rb−X bond lengths in Rb2TeCl6, Rb2TeBr6, and Rb2TeI6 are 3.152, 3.282, and 3.515 Å, respectively. Because of the symmetry reduction from Oh to D3d, the triply degenerate t MOs split into: t1u → a 2u +eu , t 2g → eg +a1g , t 2u → a1u +eu , and t1g → a 2g +eg
As can be seen from the correlation diagram (Figure 4), the HOMO−LUMO energy interval decreases from Cl to I and is 4.40 (4.20) eV for chlorides, 4.07 (3.72) eV for bromides, and 3.40 (3.18) eV for iodides. The analysis of the AO contributions to the MO of the fragments showed that, for the neutral Rb2TeX6 fragment in the valence region, there is practically no mixing of the rubidium AO with the AOs of the Te atoms and halogens. However, in the charged fragment, there is mixing because of the additional charge. The largest contributions of the Te atoms are localized on MOs 1a1g, 2a1g, 2t1u, and 3a1g. The 1a1g molecular orbital makes a significant contribution to Te−X bonding because of the Te 5s−Xs overlap, and the 1t1u and 1eg MOs contain predominant contributions from the s-AOs of the halogens. The contributions of the halogen p-orbitals strengthen the Te−X binding, and the contributions of the s-orbitals, unlike
Figure 3. MO shapes of the [TeI6]2− anion. C
DOI: 10.1021/acs.inorgchem.9b00250 Inorg. Chem. XXXX, XXX, XXX−XXX
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and the participation in the Te−X covalent bonds of both 5p and 5s AOs. The maxima and bands observed in the theoretical spectra and their positions and intensities are determined by the energies of the MOs and the ionization cross sections of the electronic levels (Table 1). The shifts of the energy scale of the theoretical spectra for chlorides, bromides, and iodides were 3.48, 3.75, and 3.25 eV. In the experimental spectra of Rb2TeX6, the intense band 1 is caused by the group of nonbonding p-orbitals of the halogens, which are correlated with the 1t2g62eg43t1u61t2u61t1g63a1g2 MOs of the regular octahedral [TeX6]2−. Band 2 corresponds to the bonding 2t1u6 MO (Te 5p + Inpσ halogen). Band 3 in the range of 12−15 eV is mainly due to the Rb 4p MO. The Rb 4p1/2 MO and 2a1g2, 1t1u6, 1eg4, and 1a1g2 MOs of the anion contribute to band 4. In the series from Cl to I, it is noticeable that the first band in the spectra of the valence electrons shifts to lower energies, which is confirmed by the correlation diagram (Figure 5). The changes in the energies of the upper occupied levels in the Cl, Br, and I series are due to the different radii of the halogen atoms and the lower binding energies of the 4s and 5s, as well as 4p and 5p, electrons of Br and I relative to the binding energies of the 3s and 3p electrons of chlorine. The most similar energies to the experimental values are those of the fragments corresponding to the experimental and optimized D3d geometries. The fragments of Oh symmetry, because of the positive charge (+6), show a shift of the Rb 4p band toward lower energies. The discrepancies in the energy intervals between the calculated results and the binding energy have three main causes: the difference in the geometry of the calculated fragments from the real structure of the crystals, the effect of the electronic level on the energies of the Kohn−Sham MOs, and the dependence of the relaxation energy in the final state on the type of electronic level. Systematics of Excited States. As we have shown previously,37,39 transitions between the excited 3T1u and ground 1A1g states are responsible for the luminescence of this class of compounds. According to the selection rules, transitions to triplet states are prohibited both because of the spin and the total moment; however, this prohibition is lifted due to the spin−orbit interaction in heavy atoms. Because of the lack of mixing of the AOs of the cations and anions in the first HOMO, when studying the luminescence mechanism, we can restrict ourselves to considering only free anions. The consideration of the effect of the spin−orbit interactions on the systematics of the [TeX6]2− anions is possible in double point groups by the direct multiplication of the irreducible representations of the spatial and spin wave functions.46 In the octahedral point group (Oh), the symmetry of the spin function of the triplet T1g states leads to the 3T1u states via the following multiplication: T1u × T1g = A1u + Eu + T1u + T2u. Consequently, when classifying the states in double point groups for the 1A1g → 3T1u spin-prohibited excitation, the T1u transition operator “allows” the radiative transition to one of four states, i.e. T1u. The splitting of the energy of the lower T1u excited state because of the electron−vibrational interactions follows from the antibonding character of the 3a1g HOMO and 4t1u LUMO. In the excited 3a1g14t1u1 configuration, the removal of one electron from 3a1g leads to a decrease in the interatomic
1a1g, are antibonding. The main role in the covalent bonding of Te−X is played by six electrons in the 2t1u MO, which forms the Te 5p−Xpσ interaction. When considering the degree of ionicity of the bonds and the X → Te charge transfer processes in the excited state, the nonbonding 1t2g2eg3t1u1t2u1t1g MOs localized by 97−100% on the halogen atoms are significant. Considering the orbital analysis, we conclude that, to understand the mechanism of luminescence and its quenching, it is necessary to consider the upper 3a1g1t1g3t1u1t2u2eg1t2g MOs. There is practically no effect of the cations on these MOs. Thus, we can limit our discussion to the consideration of the free anions alone. The order of the electronic levels of the anions in Rb2TeX6 (Figure 4) is similar to the order of levels of the free anions (Figure 5).
Figure 5. Energy diagram of valence MOs of [TeX6]2− octahedral anions.
In free anions (Figure 5), the HOMO−LUMO energy interval decreases from Cl to I and is 4.19 eV for [TeCl6]2−, 3.70 eV for [TeBr6]2−, and 3.23 eV for [TeI6]2−. The change in the HOMO−LUMO interval is related to the size of the halogen atom and the reduction in the contribution of the Te 5s orbital to the 3a1g MO. The contribution of the Te 5s orbital to the 3a1g MO for the free anions decreases in the following order: [TeCl6]2− (13%) > [TeBr6]2− (10%) > [TeI6]2− (7%). The sequence in neutral Rb2TeX6 is similar. The positions of the 2t1u MOs in [TeCl6]2− and [TeBr6]2− are approximately the same. In addition, the destabilization of the 2t1u2a1g1eg1t1u1a1g MOs takes place in [TeI6]2− because of the close location of the energy levels of the Te and I atoms. Theoretical and Experimental XPS Spectra of Rb2TeX6. The calculated results for the energies and composition of the model fragments show good agreement with the XPS spectra of the valence electrons (see Figure 6) D
DOI: 10.1021/acs.inorgchem.9b00250 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 6. Experimental XPS spectra of the valence region: (a) Rb2TeCl6, (b) Rb2TeBr6, and (c) Rb2TeI6 and theoretical spectra taking into account the spin−orbit splitting of Rb 4p for model fragments with experimental (x1, Oh; x3, D3d) and optimized (x2, D3d) geometries, where x = a, b, and c.
bond length is 2.591 Å; for [TeI6]2−, the Te−I bond length is 3.014 Å. In the 3A2u excited state for [TeCl6]2−, the Te−ClA axial bond length is 3.156 Å, and the Te−ClE equatorial bond length is 2.602 Å. For [TeI6]2−, the axial and equatorial Te−I bond lengths are 4.023 and 3.060 Å, respectively. In the 1A2u excited state, the bond lengths in [TeCl6]2− are 3.116 and 2.511 Å for Te−ClA and Te−ClE, respectively. In [TeI6]2−, the bond lengths are 3.643 and 2.931 Å for Te−IE and Te−IA, respectively. The spatial distribution of the electron density of the 3a1g orbital strongly differs in the ground and excited states (Figure 7). The compositions of the MOs of the ground and first excited states of the [TeCl6]2− and [TeI6]2− anions according to the CASSCF (8,7) data are presented in Table 2. In the 1A1g ground state, the 3a1g orbital has a smaller and nodal surface (Figure 7), whereas, in the 3A2u state, it has a more elongated shape (tetragonal elongation). In the ground state, the contributions of the Te 5s orbital to the 3a1g orbital are 12% for [TeCl6]2− and 8% for [TeI6]2−.
distances of all Te−X bonds, and an electron on one of three 4t1u MOs increases the length of only two axial Te−X bonds, resulting in D4h symmetry. The irreducible representations of the spin wave function of the D4h group for the singlet state are A1g and, for the triplet state, A2g + Eg. The multiplication of the irreducible representations of the spatial and spin wave functions for the D4h group leads to the following states: A2u × A1g = A2u; A2u × A2g = A1u; A2u × Eg = Eu. Analysis of the First Excited State. According to the CASSCF(8,7) calculations, where eight active electrons are located on seven active molecular orbitals (Figure 7), the three MOs corresponding to 1t1g in Oh or a2g and eg in D4 are occupied by six electrons, and two remaining electrons participate in the formation of the excited states. The first excited states of the anions in the D4h group correspond to the transitions of one electron from the 3a1g HOMO to the a2u LUMO orbital, forming the electron configuration 3a1g1a2u1eu0 corresponding to the singlet and triplet states, 1A2u and 3A2u, respectively, with different spin inversion. In the 1A1g ground state, the axial (Te−XA) and equatorial (Te−XE) bond lengths are equal. For [TeCl6]2−, the Te−Cl E
DOI: 10.1021/acs.inorgchem.9b00250 Inorg. Chem. XXXX, XXX, XXX−XXX
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symmetry group, all bond lengths stretched with a step of 0.1 Å, corresponding to the fully symmetric vibration, v1. At an internuclear distance of 3.3−3.5 Å, the intersection of the curves is observed. This intersection indicates the possibility of mixing the ground and first triplet excited states. Because [TeI6]2− anions have longer bond lengths and correspondingly mean amplitudes smaller than those of [TeCl6]2−, a slight increase in the bond length, for example, arising from internal conversion with the transition of the excitation energy to the oscillation energy of the nuclei (i.e., heating the sample), leads to the possibility of luminescence quenching of the second order. In this case, a decrease in the quantum yield is caused by the increase in the probability of a nonradiative transition with an increase in vibrational energy. Because of the smaller radii of the chlorine nuclei and correspondingly shorter bond lengths, the [TeCl6]2− anions exhibit greater mean amplitudes and greater tetragonal elongation and tetragonal compression, which leads to a larger energy gap between 1A1g and 3A2u states and a lower probability of luminescence quenching.
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Figure 7. HOMO shapes and distributions of electrons in the ground and excited states. Demonstration of the Jahn−Teller tetragonal elongation corresponding to the v2(eg) oscillation.
CONCLUSION
This work highlights that the 1t2g2eg3t1u1t2u1t1g3a1g MO group of the regular octahedron (anion) plays the main role in the luminescence process and its quenching. The luminescence process and the HOMO−LUMO interval directly depend on the contribution of Te 5s to 3a1g MO, and the degree of ionicity of the bonds depends on the contributions of halogen p-AOs to the 1t2g62eg43t1u61t2u61t1g6 MOs. The main role in the covalent Te−X bonding is played by the six electrons in the 2t1u MO. Because of the lack of mixing of the cation and anion AOs in the first HOMO, when studying the luminescence mechanism, we can restrict ourselves to considering only free anions. Because the contribution of the Te 5s orbital of the 3a1g MO in the first excited state decreases for [TeCl6]2− to 5% (12% in the ground state) and is completely absent for [TeI6]2− (8% in the ground state), this may be a possible reason for the quenching of luminescence in the isostructural series containing [TeI6]2− anions. The second reason for luminescence quenching may be that the [TeI6]2− anions have longer bond lengths and correspondingly smaller mean amplitudes compared to [TeCl6]2−, and a slight increase in the bond length, for example, due to internal conversion with the transition of the excitation energy to oscillation energy of nuclei (i.e., heating the sample), leads to luminescence quenching of the second kind. However, for a more accurate determination of the possible cause of quenching, it is necessary to carry out spin−orbit coupled (SOC)-CASSCF calculations with a large active space and based on the representations of double point groups; this
On a HOMO−LUMO electron transition, a 1,3A2u excited state is formed. In this case, filling in one of the three LUMOs corresponding to the split 4tu (Oh) orbital in all three cases forms the 1,3A2u state. The contribution of the Te 5s orbital of the 3a1g MO in the 3 A2u state decreases to 5% for [TeCl6]2− and is completely absent for [TeI6]2−. Because the 3a1g MO is responsible for the luminescence process, the absence of the Te 5s contribution in the [TeI6]2− anion may be a possible reason for the luminescence quenching. In contrast, the contribution of the Te 5s orbital of the 3a1g MO in the 3A2u excited state of the [TeCl6]2− anion causes a difference in the overlap of electronic wave functions with neighboring atoms and contributes to a change in the equilibrium position and the ground and excited interaction constants; this could also be the source of the Stokes shift. Because of the Jahn−Teller oscillation, v 2 (e g ), the simultaneous presence of tetragonal elongation and tetragonal compression is possible. This change in the anion geometry can lead to the appearance of two luminescence bands in the spectrum, which will be associated with the features of the excited states. On a single configurational coordinate diagram of the excited energy levels (Figure 8) for the 3A2u states in the D4h symmetry group, the axial lengths of the Te−XA bonds were assumed to be fixed, and the equatorial Te−XE bonds were stretched in 0.1 Å steps. For the ground state in the Oh
Table 2. Contributions of s/p/d Electrons (%) to the Upper MOs in the 1A1g Ground and the 3A2u Excited States of [TeCl6]2− and [TeI6]2− Free Anions [TeCl6]2− 1
3
A1g
4tu 3a1g a2g(1t1g) eg(1t1g)
Te s/p/d −/−/− 12/0/0 0/0/0 0/0/0
[TeI6]2−
Cl s/p/d −/−/− 0/88/0 0/100/0 0/100/0
Te s/p/d 0/40/0 5/0/0 0/0/1 0/0/2
1
A2u Cl s/p/d 0/60/0 0/95/0 0/99/0 0/98/0 F
Te s/p/d −/−/− 8/0/0 0/0/0 0/0/0
3
A1g I s/p/d −/−/− 0/92/0 0/100/0 0/100/0
Te s/p/d 0/7/0 0/0/0 0/0/0 0/0/0
A2u I s/p/d 0/93/0 0/100/0 0/100/0 0/100/0
DOI: 10.1021/acs.inorgchem.9b00250 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 8. Single configurational coordinate diagram of 1A1g and 3A2u excited energy levels for (a) [TeCl6]2− and (b) [TeI6]2− anions.
should result in the 3A2u state splitting into two states: A1u and Eu. In this case, an important task will be the determination of their energy intervals, mixing, state lifetime, and quantum radiation yield. If the nonadiabatic interaction is neglected, spin−orbit splitting can lead to a nonradiative transition by intersystem crossing, or to a radiative transition, i.e. phosphorescence. By comparing the nonradiative lifetime with the radiative one, an exact conclusion about the most likely cause can be made.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.9b00250. Energies of MOs, AOs contributions to MOs of TeX62− free anions and anions in Rb2TeX6 (X = Cl, Br, and I), description of MOs, and theoretical XPS spectra of free anions (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Alexander A. Dotsenko: 0000-0001-7436-2213 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the Ministry of Education and Science of the Russian Federation within the framework of project part of the state task (Project 16.5904.2017/8.9 and Project 16.5906.2017/6.7).
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