B. Hari Babu

Fluorescence properties and electron paramagnetic resonance studies of γ-irradiated Sm3+-doped oxyfluoroborate glasses

The permanent photoinduced valence manipulation of samarium doped oxyfluoroborate glasses as a function of γ-ray irradiation has been investigated using a steady-state fluorescence and electron paramagnetic resonance techniques. An increase in SrF2 content in the glass led to the red shift of the peaks in as prepared glass, while in irradiated glasses this led to the decrease in defect formation as well as increase in photoreduction of Sm3+ to Sm2+ ion. The energy transfer mechanism of induced permanent photoreduction of Sm3+ to Sm2+ ions in oxyfluoroborate glasses has been discussed. The decay analysis shows exponential behavior before irradiation and non-exponential behavior after irradiation. The energy transfer in irradiated glasses increases with the increase in SrF2 content in the glass and also with the irradiation dose.

Radiation hardening in sol-gel derived Er3+-doped silica glasses

The aim of the present paper is to report the effect of radiation on the Er3+-doped sol-gel silica glasses. A possible application of these sol-gel glasses could be their use in harsh radiation environments. The sol-gel glasses are fabricated by densification of erbium salt-soaked nanoporous silica xerogels through polymeric sol-gel technique. The radiation-induced attenuation of Er3+-doped sol-gel silica is found to increase with erbium content. Electron paramagnetic resonance studies reveal the presence of E′δ point defects. This happens in the sol-gel aluminum-silica glass after an exposure to γ-rays (kGy) and in sol-gel silica glass after an exposure to electrons (MGy). The concentration levels of these point defects are much lower in γ-ray irradiated sol-gel silica glasses. When the samples are co-doped with Al, the exposure to γ-ray radiation causes a possible reduction of the erbium valence from Er3+ to Er2+ ions. This process occurs in association with the formation of aluminum oxygen hole centers...

Photoluminescence properties of Tb-Eu-Mn-codoped fluoroborate glasses under γ-irradiation

We report here an energy transfer from Tb3+ to Eu3+, Mn2+ and Eu2+ to Tb3+ and Mn2+ for an un-irradiated and γ-irradiated B2O3-Al2O3-Na2O-SrF2 glass samples, respectively. The blue emission from Eu2+ ions as well as green and red emission from Tb3+, Eu3+, and Mn2+ ions will contribute to the generation of white light while excited at 339u2009nm using a xenon lamp. Furthermore, the chromaticity color coordinates, correlated color temperature, and quantum efficiency parameters are calculated for all the glass samples, and their relative variations with respect to γ-irradiation dose are presented.

Radiation hardening of sol gel-derived silica fiber preforms through fictive temperature reduction

The impact of fictive temperature (Tf) on the evolution of point defects and optical attenuation in non-doped and Er3+-doped sol-gel silica glasses was studied and compared to Suprasil F300 and Infrasil 301 glasses before and after γ-irradiation. To this aim, sol-gel optical fiber preforms have been fabricated by the densification of erbium salt-soaked nanoporous silica xerogels through the polymeric sol-gel technique. These γ-irradiated fiber preforms have been characterized by FTIR, UV-vis-NIR absorption spectroscopy, electron paramagnetic resonance, and photoluminescence measurements. We showed that a decrease in the glass fictive temperature leads to a decrease in the glass disorder and strained bonds. This mainly results in a lower defect generation rate and thus less radiation-induced attenuation in the UV-vis range. Furthermore, it was found that γ-radiation hardness is higher in Er3+-doped sol-gel silica compared to un-doped sol-gel silica and standard synthetic silica glasses. The present work demonstrates an effective strategy to improve the radiation resistance of optical fiber preforms and glasses through glass fictive temperature reduction.

Functionalized Graphene Oxide Enables a High-Performance Bulk Heterojunction Organic Solar Cell with a Thick Active Layer

Novel functionalized graphene oxide π-π stacking with conjugated polymers (P-GO) is fabricated via a simple ethanol-mediated mixing method, leading to better dispersion in organic nonpolar solvents and bypassing the inherent restrictions of hydrophilicity and oleophobicity. We analyze the mechanism of the incorporation of P-GO into inverted organic solar cells (OSCs) based on a poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4- b]thiophenediyl]] (PTB7):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) system to investigate the possibility of high-performance thick-film OSC fabrication. It is verified that the incorporation of P-GO into the PTB7:PC71BM blend films leads to a decreased π-π stacking distance, enlarged coherence length for polymer, and optimized phase separation, resulting in more effective charge dissociation, reduced bimolecular recombination, and more balanced charge transport. The OSCs with 1% P-GO incorporation demonstrate a thickness-insensitive fill factor (57.8%) and power conversion efficiency (PCE) (7.31%) even with 250 nm thick photoactive layers, leading to a dramatic PCE enhancement of 34% compared with the control devices with the same thickness.

Femtosecond laser processing induced low loss waveguides in multicomponent glasses

We have investigated that femtosecond laser induced optical waveguides in AF32 and in Borofloat-33 glasses. Type-I positive and type-II negative refractive index change mechanisms were established in AF32 and in Borofloat-33 glass waveguides, respectively. Lowest propagation loss of 1.1 ± 0.31 dB/cm could be attained in AF32 glass, which has a typically higher index change than in Borofloat-33 glass. Resultant losses are directly correlated with densification and non-bridging oxygen hole centers, which can be authenticated by Raman and photoluminescence studies.

Study of Radiation Effects on Er3+-Doped Nanoparticles Germano-Silica Fibers

The main goal of the present work is to study the impact of Er-SiO2 and Er-Al2O3 nanoparticles on the radiation induced defects in germano-silica optical fibers with Al/Ge ranges over 0.1-150. These fibers are prepared by a modified chemical vapor deposition technique and are characterized by optical absorption and electron paramagnetic resonance spectroscopy. High amount of Ge, Er-SiO2 nanoparticles-derived optical fibers exhibit lower radiation induced attenuation than those with a low Ge content undoped or doped with Al2O3 nanoparticles. Furthermore, the behavior of point defects namely GeE, Ge(1), SiE, nonbridging oxygen hole centers, and H(1) is reported according to the Al/Ge ratio. In contrast to the optical fiber preforms, no Al-related defects are found in the optical fibers. Therefore, the results evidence the strong radiation tolerance by the virtue of the nanoparticle doping, which is enabling technology for the development of the photonic and space applications in the radiation fields.