Disorder and the optical spectroscopy of Cr³⁺-doped glasses: I. Silicate glasses

Abstract

This paper reports optical absorption and luminescence studies of Cr"-doped silicate glasses with compositions chosen to vary the octahedral crystal-field splitting at the Cr" site. The extensive site-to-site disorder in the glasses is signalled by the inhomogeneous broadening of radiative transitions and by non-exponential fluorescence decay patterns. Laser-excited luminescence shows that the octahedral crystal-field splitting Dq varies between the different sites occupied by Cr" ions. Both R-line and vz+ 'Az emissions are inhomogeneously broadened by site-to-site disorder. Fluorescence line narrowing (FLN) of the R line gives a particularly dramatic demonstration of the site multiplicity. Measurement of the width of the FLN component of the R line as a function of temperature has been used to probe the density of two-level vibrational systems coupled to the electronic levels of the C+ ion

Determination of the oxidation state and coordination of a vanadium doped chalcogenide glass

“…The C/B values calculated using the energy terms for the 2 E( 2 G) and 2 T 2 ( 2 G) levels were 4.55 and 4.25, respectively. The C/B parameter for the octahedral d 3 configuration can also be calculated using an approximate formula given by Rasheed [44] and gives very similar results to our calculations. The value of C/B calculated using for the octahedral d 3 configuration are in the allowed range of 4 to 5, unlike those calculated for the tetrahedral d 2 configuration which was 6.57.…”

Chromium-doped silica optical fibres: influence of the core composition on the Cr oxidation states and crystal field

“…When considering Dq and Dq/B values for Cr 3+ and Cr 4+ in Table 4, one sees that chromium ions are in low-to-intermediate ligand field sites, in agreement with reports on other oxide glasses, either silicates doped with Cr 3+ or aluminosilicates doped with Cr 4+ (from [8]). In our samples, Cr 3+ ions lie in the so-called 'crossing' region of the 4 T 2 and 2 E states (at which Dq/B~2-2.2) like in silicate glasses [14,15], but Dq and B are found ~90 cm -1 (6 %) and ~70 cm -1 (10 %) (in average) lower than in these glasses, respectively. This would suggest that Cr 3+ ions are submitted to a lower ligand field in the silica fibres than in classically prepared glasses, and that the covalency of their bonding to the glassy network is increased [20].…”

Cr3+-doped LiNbO3 crystals grown by the Bridgman method

“…The strength of the octahedral crystal field, Dq, and the Racah parameters B and C are given by the following equations [15]: …”