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Based on the 6-membered ring cluster model, geometric and optical properties of cluster model of Yb-doped silica optical fiber is researched by using first-principles calculations. It can be revealed that the interstitial Yb-doped model is geometrically and optically closer to the local structures of Yb-doped silica optical fibers. In interstitial Yb-doped model, the coordination number of Yb to O is 6, and the oscillator strengths of excited levels are stronger than the substitutional Yb-doped model. We construct the Yb–Al co-doped and Yb–P co-doped models based on the interstitial Yb-doped model, and calculate the absorption spectra of these co-doped models. It can be proposed that co-doping with Yb and Al is responsible for the ~ 1030 nm absorption. [ABSTRACT FROM AUTHOR]

Abstract We report first-principles calculations of cluster silica with and without interstitial Bi0 atom. The size and radial distance of "Si-O-Si" rings are considered to study the equilibrium position of interstitial Bi0 atom in Bi-doped silica optical fiber. Our results reveal that the interstitial Bi0 atom is most likely to stay around ~ 2 Å from the center of 6-membered rings. By comparing the transition energy levels with Bi0 atomic spectral data, we find that the transition 2D 3/2 (1) → 4S 3/2 of interstitial Bi0 atom leads to the NIR emission estimated as ~ 1265 nm in Bi-doped silica optical fiber. Our methods will be effective to confirm bismuth-active centers for different valence states of Bi atom. [ABSTRACT FROM AUTHOR]

Monovalent bismuth-related centers are studied by using first-principle methods in Bi-doped silica optical fiber. On the basis of 6-membered ring (6MR) model, the nBi-doped 6MR models are constructed for studying geometric and optical properties. With the quantity of monovalent bismuths increasing from one to three in 6MR model, the optical absorption intensity showed a trend of first increase and then decrease. The transition energy levels of monovalent bismuth-related model are studied with the time-dependent density functional theory (TDDFT). Our results showed that the 3P 1 → 3P 0 transition of Bi + ion gives rise to near-infrared (NIR) luminescence around 1270 nm. • The possible micro-structure of Bi+ was constructed in Bi-doped silica optical fiber. • Bi-cluster will be generated when Bi atoms are excessive and further inhibit the absorption intensity. • The 2Bi-6MR-2 model can give rise to the optical absorptions at ∼500 nm and ∼700 nm. • The NIR luminescence around 1270 nm is due to the 3P 1.→ 3P 0 transition of Bi + ion. [ABSTRACT FROM AUTHOR]

The interaction mechanisms of interstitial Bi0 with intrinsic defects in bismuth-doped silica optical fiber are investigated by first-principles calculations. The results reveal that interstitial Bi0 easily interact with peroxygen defects and the reaction products are more stable. By analyzing the effective charges of the reaction products of interstitial Bi0 interacting with peroxy linkage (POL), non-bridging oxygen hole center with silicon dangling bond (NBOHC-Eʹ), and peroxy radicals with silicon dangling bond (POR-Eʹ), it finds that Bi atom is nearly divalent. For interstitial Bi0 interacting with oxygen deficiency center (ODC(I)), it forms a complex with two Si atoms in the defect. The method will be effective to understand interaction mechanism of interstitial Bi0 with intrinsic defects in bismuth-doped silica optical fiber. [ABSTRACT FROM AUTHOR]

Bi/Er co-doped silica optical fiber is investigated by using first-principle methods. Si–Bi–Er and Si–O–Bi–Er cluster models are constructed based on the interstitial Er-doped 6-membered ring (Int-Er-6MR) model for investigating the geometric and optical properties. The formation energy decreases with the increase of the Bi–Er bond length, and the Si–O–Bi–Er model is more stable than Si–Bi–Er model. Our results confirm that ~1270 nm luminescence originates from Bi+ ion and ~1530 nm luminescence stems from Er3+ ion. Besides, we discuss the possible energy transfer processes between Bi+ ion and Er3+ ion. • Si–Bi–Er and Si–O–Bi–Er cluster models in Bi/Er co-doped silica fiber are studied. • Classical MD, BSE and HSE methods are applied in this work. • Optical absorption and luminescence of Bi/Er co-doped silica fiber are researched. • Possible energy transfer processes between Bi+ and Er3+ ion are discussed in theory. [ABSTRACT FROM AUTHOR]