Unraveling the hidden Urbach edge and Cr6+ optical transitions in borate glasses

Precise determination of optical band gap in Cr-doped semiconductor nanowires

“…Similar gap size discrepancies can be found in other gapped systems, such as glasses, when doped with TMs. The band gap in Cr-doped borate glasses, for example, was reported to be ~1.3 eV smaller than the typical value for borate glasses [41,42] , while recent studies claim barely affected (± 0.2 eV) band gap due doping [43,44] . In fact, on theoretical bases, one should not expect large band structure variations (except for energy shifts) or gap size modulation for doping level as diluted as dopants per more than six-unit cells [45,46] .…”

Multiple optical features in binary-transition-metal borate glasses

“…We utilized this strategy to distinguish features originating due to Cr ions from those resulting from Cu ions. It is clear that there are three signals in the Cu-free sample (x = 0), two of which are located at the low eld side with effective g values 4.82 and 4.08, and are often attributed to the presence of Cr 3+ [4,[10][11][12][13][14]27]. The absorption at g = 2.25 is due to exchange coupled pairs or large Cr 3+ clusters, while the resonance located at high eld with an effective g value of 1.93 is mainly due to Cr 6+ [10,28].…”

“…Chromium (Cr), among other TM ions, is enormously important for the development of tunable solid state lasers, optical bers, and as active component in luminescence materials, as it can exist in different oxidation states, the most abundant of which are Cr 3+ and Cr 6+ [7][8][9][10]. Moreover, Cr ions also act as glass modi ers, so that these distinctive oxidation states within the structural units constituting the glass could be regulated by suitable selection of the glass modi ers/formers, by the size and eld strength of the ions, and eventually by the mobility of the modi er cations [10][11][12][13][14]. Optical transitions solely stemming from Cr ions can span the ultraviolet (Cr 6+ ) and visible (Cr 3+ ) spectral regimes, the former could be readily identi ed for diluted Cr ion concentrations [14].…”

“…Moreover, Cr ions also act as glass modi ers, so that these distinctive oxidation states within the structural units constituting the glass could be regulated by suitable selection of the glass modi ers/formers, by the size and eld strength of the ions, and eventually by the mobility of the modi er cations [10][11][12][13][14]. Optical transitions solely stemming from Cr ions can span the ultraviolet (Cr 6+ ) and visible (Cr 3+ ) spectral regimes, the former could be readily identi ed for diluted Cr ion concentrations [14].…”

Influences of copper–potassium ion exchange process on the optical bandgaps and spectroscopic properties of Cr3+/Yb3+ co-doped in lanthanum aluminosilicate glasses

“…6,7 Chromium is a transition metal (TM) with many different valence states. [8][9][10] In the glass networks, it oen exists in the trivalent state Cr 3+ , [1][2][3][4][5]8 which can emit radiation in the visible (VIS), near-infrared (NIR) regions under different excitation wavelengths. 5,11,12 Also, the 4 T 1g (F) / 4 A 2g , 4 T 2g (F) / 4 A 2g , 2 T 1g / 4 A 2g , 2 T 2g / 4 A 2g and 2 E / 4 A 2g transitions of Cr 3+ can be combined with Yb 3+ to generate the VIS, NIR emission spectra.…”