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

Abstract

Vanadium doped chalcogenide glass has potential as an active gain medium, particularly at telecommunications wavelengths. This dopant has three spin allowed absorption transitions at 1100, 737 and 578 nm, and a spin forbidden absorption transition at 1000 nm. X-ray photo electron spectroscopy indicated the presence of vanadium in a range of oxidation states from V + to V 5+ . Excitation of each absorption band resulted in the same characteristic emission spectrum and lifetime, indicating that only one oxidation state is optically active. Arguments based on TanabeSugano analysis indicated that the configuration of the optically active vanadium ion was octahedral V 2+ . The calculated crystal field parameters (Dq/B, B and C/B) were 1.85, 485.1 and 4.55, respectively. IntroductionDetermination of the oxidative state of an active ion dopant is important for optical device applications as it determines the energy levels within the material available for use. Knowledge of the oxidation state is therefore needed when modelling the radiative and non-radiative transitions that occur in an optical material. The oxidation states of transition metal ions are particularly difficult to identify by spectroscopy as their bonding d electrons also determine their electronic energy levels and they are therefore strongly dependent on both the strength and the arrangement (coordination) of the neighbouring atoms electric field. In contrast, rare-earth metals, in which the electronic energy levels are determined by the 4f electrons which do not take part in bonding and are shielded by the 5s5p electrons, the oxidation state can be identified relatively easily by spectroscopy. Amorphous glass hosts, with their tendency to result in mixed oxidation states due to significant variation in the local environment, lead to a complex superposition of electronic states when doped, which exacerbates the problem of spectroscopic analysis of transition metals.Chalcogenide glasses often exhibit low phonon energy and this allows the observation of optical transitions in dopants that are not observed in traditional glasses such as silica. Gallium lanthanum sulphide (GLS) has a transmission window of ~0.5-10 ?m [1], a high refractive index of ~2.4, and a low maximum phonon energy of ~425 cm -1 which results in low non-radiative decay rates [2]. These properties allowed the observation of low-energy transitions which are not seen in other hosts, for example the first observation of the 4.9 ?m fluorescence from the 5 I 4 > 5 I 5 transition of Ho 3+ [3]. Also, rarely observed Ti 3+ emission [4] and long-wavelength emission from Bi [5] have both also been reported from GLS host glasses.

Crystal field analysis of Dy and Tm implanted silicon for photonic and quantum technologies

“…However, comparatively little is known about the local environment of optically active RE ions implanted into silicon, which limits the optimisation of this technology. The atomic shielding of the f-shell electrons in REs means that the effect of the host crystal field on their energy levels is weaker when compared with transition metal ions [4,5] or bismuth [6,7]. Nevertheless, the complex f-shell inter-electron (coulomb) and spin-orbit interactions, along with the simultaneous influence of the crystal field, give rise to intricate energy level splitting that is highly dependent on the local crystal field environment of the RE and can reveal detailed structural information.…”