Cubic-symmetry DX-like state of an In center in semiconducting CdF2

First-Principles Study of Structural Bistability in Ga- and In-DopedCdF2

“…The DX center is stable only in a negative charge state and hybridization between impurityd and Cd-d electrons is found to play an indispensable role in stabilizing it. The proposed DX state explains the major experimental observations on the properties of deep centers in CdF 2 [3][4][5][6]9,10,29].…”

“…The phenomenon of bistability in which a dopant atom has both effective-mass hydrogenic ("shallow") and highly localized deep states is well known in many III-V and II-VI zinc blende semiconductors and has been extensively studied [1,2]. Surprisingly, the same type of bistability is observed in the very-large-band-gap fluorite structure compound CdF 2 when doped with Ga or In donor impurities [3][4][5][6][7][8][9][10]. Experimental data on the absence of a paramagnetic moment for the deep center [5], a quantum yield of two electrons per photon for the deep-shallow transition [6], the bimolecular nature of the shallow center thermal decay [4,6], self-compensation, a relatively large energy barrier between the shallow and deep states [6], a large Stokes shift between thermal and optical ionization energies, persistent photoconductivity [3], photoinduced lattice shrinkage [8], and recent positron annihilation measurements [11] showing an open-volume defect occurring upon DX center formation indicate that the deep center in In-and Ga-doped CdF 2 is a negative-U center with a large lattice relaxation.…”

“…The D 1 sym state can capture a free electron [4,7,10] and transform into a D 0 sym . A second electron capture is found to lead to a metastable D 2 sym state with large outward relaxations of the nearestneighbor F atoms.…”

Raman spectroscopy characterization of Li2CaHfF8crystals

“…However, as can be inferred from table 1, only three A 1 modes would be observed in the x(zz)x geometry, contrary to our experimental results. Several sets of experimental data from Raman scattering and infrared spectroscopy have been reported for LiYF 4 and LiLnF 4 (Ln = Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) [4][5][6][7][8][9][10][11][12] crystals. In CaWO 4 isomorphous crystals, the internal vibrations of WO 2− 4 dominate the spectra and are little shifted from the free-ion frequencies.…”

“…Several studies have already been reported concerning the spectroscopy characterization of LiMF 4 compounds [4][5][6][7][8][9][10][11][12]. For instance Salaün et al [10] studied the lattice dynamics of the fluoride scheelites LiYF 4 and LiLnF 4 (Ln = Ho, Er, Tm and Yb) by means of Raman, infrared and inelastic neutron scattering, while Zhang et al [9] studied, by means of Raman spectroscopy, the crystalline structure of LiGdF 4 .…”