Time-resolved spectroscopy in LiCaAlF₆doped with Cr³⁺: dynamical Jahn–Teller effect and thermal shifts associated with the⁴T₂excited state

Abstract

This work investigates the centre distribution of the Cr(3+) impurity, the dynamical Jahn-Teller effect in the first (4)T(2) excited state and the thermal shifts of the absorption and emission peaks in LiCaAlF(6):Cr(3+) by means of time-resolved emission spectroscopy. The electronic and vibrational fine structure observed in both the absorption and emission spectra at low temperature are assigned according to the vibrational modes of the internal (CrF(6))(3-) complex and the lattice modes. Zero-phonon lines associated with (4)T(2) --> (4)A(2) and (2)E --> (4)A(2) transitions were detected and assigned on the basis of available high pressure data in LiCaAlF(6):Cr(3+). We have identified the vibrational coupled modes responsible for the vibrational structure of the low temperature emission spectrum and the reduction of the zero-phonon line (ZPL) splitting caused by the dynamical Jahn-Teller effect in the (4)T(2) excited state (Huang-Rhys factor, S(e) = 0.92). In addition, from the temperature variation of the emission intensity I(T), transition energy E(T) and bandwidth H(T), we obtained the vibrational modes that are coupled to the emitting state. We have evaluated the two main contributions to the photoluminescence thermal shift through thermal expansion and high pressure measurements: the implicit contribution induced by changes of thermal population and the explicit contribution induced by thermal expansion effects--40% and 60% of the total shift, respectively.

Molecular geometric phase from the exact electron-nuclear factorization

“…[40][41][42][43][44][45] Berry phase effects are also relevant to some dynamical Jahn-Teller systems which have been investigated recently. [46][47][48][49][50][51][52][53] In many of these cases, the exact factorization could provide an interesting alternative to conventional approaches based on the adiabatic expansion of Eq. ( 4).…”

Minimizing Bond Angle Distortion to Improve Thermal Stability of Cr3+ Doped Near‐Infrared Phosphor

“…However, Cr 3+ is proved to enter solely [AlF 6 ] octahedron [ 17 ] for similar radius [ 18 ] and same valence. [ 19 ] Every [AlF 6 ] octahedron is corner‐sharing with six [SrF 6 ] octahedron resulting in the [AlF 6 ] octahedron isolating from each other. [ 20 ] Elemental analysis in Table S1 and Figures S2 and S3 in the Supporting Information shows the designed stoichiometry translates to the product composition.…”

“…The effective phonon energy obtained from fitting ħω = 250 cm −1 , similar to the former calculated effective phonon energy of 246–255 cm −1 . [ 19 ] The activation energy Δ E increases from 0.479 eV of x = 0 to 1.166 eV of x = 1. Overall, the Mott‐Seitz process dominates the significantly suppressed TQ in this case.…”

“…This conclusion is in line with the previous report that the effective phonon energy locates at 246–255 cm −1 . [ 19 ] Because A 2 and A 3 are originated from spin–orbit interaction, t 2u phonon replica may soften the 4 T 2g excited states of Cr 3+ through a dynamical mechanism. The phonon replica at 483 cm −1 , ascribed to the overlap of two sources: e g and t 2g +t 2u , shows a slight increase in intensity from 0.17 to 0.28.…”

Photoluminescence of monoclinic Li3AlF6 crystals under vacuum ultraviolet and soft X-ray excitations

“…This applies not only to study of the crystal structure [9], but also to study of the luminescence and optical properties of both the undoped crystals [10][11][12], and crystals doped with Ce 3+ [13,14], Cr 3+ [15], and Pr 3+ [16]. Electronic properties of undoped Li M AlF 6 crystals have been studied experimentally using vacuum ultraviolet optical and luminescence spectroscopy [12,17], and X-ray photoelectron spectroscopy techniques [17].…”