Rajan Jose

Intense ultraviolet emission from Tb3+ and Yb3+ codoped glass ceramic containing CaF2 nanocrystals

A transparent Tb3+ and Yb3+ codoped oxyfluoride glass ceramic containing CaF2 nanocrystals was developed. This glass ceramic showed an intense ultraviolet emission at 381nm due to the G65, D35→F67 transitions of Tb3+ ion when excited with a 974nm laser at room temperature. The observed intense ultraviolet emission could be attributed to the change of ligand field of Tb3+ and Yb3+ ions due to the incorporation of some Tb3+ and Yb3+ ions into CaF2 nanocrystals, and the resulting increased branching ratio of the transitions and longer lifetime of D45 level of Tb3+ in the glass ceramic.

White-light-emitting CdSe quantum dots synthesized at room temperature

White-light-emitting CdSe quantum dots (QDs) were synthesized at room temperature (RT, ∼23°C) using an organometallic colloidal growth process. These QDs are characterized by high and reproducible quantum yields (ΦPL∼0.4) as well as by unusual spectral broadening [full width at half maximum (FWHM) ∼150nm) despite of their observed size monodispersity. Surface functionalization of these quantum dots using mercaptosuccinic acid made them soluble in water. A change of color together with an enhancement in ΦPL was observed upon surface functionalization.

Stimulated Raman scattering in tellurite glasses as a potential system for slow light generation

In this article, slow light generation via stimulated Raman scattering (SRS) in tellurite-based glasses is investigated based on characterization of Raman gain coefficients and an evaluation method of slow light generation we developed. The effects of different heavy metal oxides additions on slow light generation via SRS in tellurite-based glasses are also discussed. Our results show that designed tellurite-based glass is a promising candidate for slow light generation via SRS.

Raman scattering characteristics of the TBSN-based tellurite glass system as a new Raman gain medium

A study was initiated to understand requirements for widening and flattening the gain spectra of tellurite-based glasses for their application as new gain media for photonic devices. For this purpose, two Raman active components, WO3 and P2O5, were added either separately or jointly to a TeO2-BaO-SrO-Nb2O5 (TBSN) glass system, and the Raman spectral evolution in response to this addition was studied. Raman scattering cross sections of the TBSN glasses were increased with an increase in the WO3 content and decreased with an increase in the P2O5 content. The Raman intensity and bandwidth increased when WO3 and P2O5 were jointly added in TBSN. The bandwidths of the Raman gain coefficient spectra of the present tellurite glasses were more than twice that of a conventional TeO2-Bi2O3-ZnO-Na2O glass and 70% larger than that of silica glass. The new glasses are expected to be candidates for ultrabroadband fiber Raman amplifiers.

Crystallization kinetics and spectroscopic investigations on Tb3+ and Yb3+ codoped glass ceramics containing CaF2 nanocrystals

Transparent Tb3+ and Yb3+ codoped oxyfluoride glass ceramics containing CaF2 nanocrystals were prepared by melt quenching and subsequent heat treatment. Crystallization kinetics of CaF2 nanocrystals was investigated by differential scanning calorimetric method. The average apparent activation energy Ea of the crystallization was ∼498kJ∕mol. Moreover, the value of the Avrami exponent n was 1.01. These results suggest that the crystallization mechanism of CaF2 is a diffusion controlled growth process of needles and plates of finite long dimensions. X-ray diffraction patterns and transmission electron microscopy image confirmed the CaF2 nanocrystals in the glass ceramic. Ultraviolet (UV) and visible emission spectra of the as-made glass and the glass ceramic with an excitation of a 974nm laser diode were recorded at room temperature. An intense UV emission at 381nm was observed in the glass ceramic. The origin of the enhancement of the emission at 381nm was investigated using spectroscopic technique and Judd...

Enhanced Raman gain coefficients and bandwidths in P2O5 and WO3 added tellurite glasses for Raman gain media

The Raman gain coefficient and bandwidth of tellurite glasses have been tailored by systematically adding WO3 and P2O5 in a TeO2–BaO–SrO–Nb2O5 glass system. The Raman gain coefficients of the resultant glasses were obtained from spontaneous Raman scattering experiments using a 633nm laser. The glasses developed here showed the widest gain bandwidths so far achieved in tellurite glasses while maintaining higher gain coefficients. The gain bandwidths of these glasses were more than twice that of a conventional tellurite-based glass and 70% larger than that of the silica glass.

Tailoring of Raman gain bandwidth of tellurite glasses for designing gain-flattened fiber Raman amplifiers

The issue of widening the Raman spectral bandwidth of tellurite glasses while maintaining higher scattering intensity is addressed. Raman spectral bandwidths of tellurite glasses are widened by using a single Raman active component of suitable concentration in appropriate base glasses. It was observed that the MoO6 octahedra, due to their high octahedral distortion, have high Raman polarizability compared to WO6, NbO6, and TaO6 octahedra and PO4 tetrahedra. This high Raman polarizability enabled broadening of the spectral width up to ~350 cm−1 while maintaining high Raman scattering intensities. Although similar bandwidths could be achieved using the combined generation of WO6 octahedra and PO4 tetrahedra, the resultant Raman scattering intensity of such glasses is only half of that, which could be achievable using MoO6. It is shown that the simplest tellurite glass showing wide spectral broadening is a quaternary system comprising a network modifier (BaO or Bi2O3) and two Raman oscillators (NbO6 and MoO6 octahedra).

Optical properties of MoO3 containing tellurite glasses

It was observed that P2O5 generates TeO5+δ groups in tellurite glasses that have a profound influence on their optical properties. The presence of TeO5+δ groups in phosphotellurite glass made MoO3 behave in a different way compared to other tellurite glass systems that do not contain P2O5. The refractive index measurements and Raman spectroscopy were combined to show that the addition of MoO3 in a phosphotellurite glass generates TeO3+1 polyhedron, whereas it generates TeO3 trigonal bipyramids in other glass systems. The MoO3 system showed absorption bands corresponding to Mo5+ ion in phosphotellurite glasses, whereas no similar bands were observed for other glasses.

Enhanced Nonlinear Susceptibility in TeO2–BaO–SrO–Nb2O5 Tellurite Glasses

We added systematically WO3 and P2O5 in a TeO2–BaO–SrO–Nb2O5 (TBSN) glass system, which are proposed for ultra-broadband Raman amplifiers. The response in nonlinear indices to this addition was studied and reported herewith. The third-order optical susceptibility (χ3) measured using Maker fringe analysis increased with an increase in WO3 content and decreased with an increase in P2O5 content. When these components were added simultaneously, we observed that their χ3 reaches a value similar to that of pure TeO2 glass. In view of their higher Raman gain coefficient and amplification bandwidth and with the present result of higher nonlinear indices, these glasses are likely to be suitable for photonics applications.

New P2O5 and WO3 Doped Tellurite Glasses as Broadband Raman Gain Media

New tellurite-based glasses as broadband Raman gain media are developed to realize high performance fiber Raman amplifiers. These performances are achieved by WO3 and P2O5 doping in TeO2–BaO–SrO–Nb2O5 (TBSN) glass. The maximum gain coefficient obtained in the present study was ~50 times that of silica glass for 532 nm excitation. The bandwidth (i.e., full width at half maximum) of these doped glasses was more than twice that of a conventional tellurite-based glass and 70% larger than that of silica glass.