Atul D. Sontakke

Enhanced 2 μm broad-band emission and NIR to visible frequency up-conversion from Ho3+/Yb3+ co-doped Bi2O3-GeO2-ZnO glasses.

In this work, a new and non-conventional oxide glass composition based on Bi2O3-GeO2-ZnO system has been formulated with an aim to realize low phonon oxide glass and elucidate its performance when co-doped with Ho(3+)/Yb(3+) for the energy transfer based NIR emission at 2 μm from Ho(3+) ions under Yb(3+) excitation. The glass with 1.0 mol% Ho2O3 and 0.5 mol% Yb2O3 has exhibited maximum energy transfer rate (3602 s(-1)) and energy transfer efficiency (65.92%). Important radiative properties have been predicted for emission transitions of Ho(3+) ions using intensity parameters derived from measured absorption spectra using standard Judd-Ofelt theory. At lower acceptor ion concentration (0.1 mol%), an efficient NIR to visible up-conversion emission has been observed based on two photon absorption process which has found to be reduced significantly at higher Ho(3+) concentrations with simultaneous enhancement in 2 μm emission. Hence, this newly developed glass codoped with Yb(3+)/Ho(3+) is promising glass for sensitized 2 μm emission applications as broad band tunable lasers because of the combination of low phonon energy (707 cm(-1)), high energy transfer efficiency, moderately high emission cross-section (5.33×10(-21) cm(2)) and larger effective half-width of the emission band value of 169 nm.

Efficient ~2.0 μm emission from Ho 3+ doped tellurite glass sensitized by Yb 3+ ions: Judd-Ofelt analysis and energy transfer mechanism [Invited]

The ~2.0μm emission characteristics of Ho3+ both by direct excitation and through Yb3+ sensitization in barium-tellurite glass are reported. The radiative properties of active ions have been evaluated by applying Judd-Ofelt theory on the measured absorption spectrum. A significant enhancement of Ho3+ emission (2.0μm) observed with 12 fold decrease of Yb3+ emission (1008nm) in co-doped sample entrenched the efficient energy transfer from Yb3+:2F5/2→Ho3+:5I6. The host phonon assistance in the energy transfer process has been conferred by using Dexter model. Comparatively better emission properties (Arad, Δλeff, σem) reveal that, the present material could be promising for laser emission at ~2.0μm.

Study on Tb3+ containing high silica and low silica calcium aluminate glasses: Impact of optical basicity

Two series of glasses based on high silica (CAS) and low silica calcium aluminates (LSCA) have been investigated for their structural, optical and Tb(3+) luminescence properties. The compositional modification reduces host phonon energy in LSCA glasses. Still, LSCA glasses exhibit Tb(3+) green luminescence quenching, whereas no quenching observed in CAS glasses. Material property influence on this behaviour has been discussed with an insight into the redox state of active ions.

Broadband Er 3+ emission in highly nonlinear Bismuth modified Zinc-Borate glasses

Broadband NIR emission from Er3+ in highly nonlinear zinc-bismuth-borate glasses with full width at half maximum reaching up to 106 nm is reported. The glass compositional effects on thermal, structural, optical and spectroscopic properties have been explored in view of all-optical communication applications. The Zero Dispersion Wavelength of these glasses is found to be varying from 1.46 to 2.26μm. The observed enhancement in fluorescence intensity, lifetime and quantum efficiency of 4I13/2 → 4I15/2 transition with bismuth addition is attributed to reduced multiphonon relaxations with decreased host phonon energy. The gain profile covering C and L-bands of communication windows suggests their potentiality in broad-band amplification.

Yb 3+ ion concentration effects on ∼1 μm emission in tellurite glass

The effects of Yb3+ ion concentration on physical, optical, and spectroscopic properties have been studied in a low phonon (∼590u2009u2009cm−1) barium-lanthanum-tellurite glass. Due to the unfeasibility of Judd-Ofelt theory Yb3+-doped systems, the oscillator strength of absorption transition, F27/2→F5/22 has been evaluated by using the Smakula equation. The nature of emission from F25/2→F7/22 transition of Yb3+ ions is described theoretically by using a rate equation in comparison with experimental results. By applying reciprocity (RM) and Fuchtbauer-Ladenburg methods on emission spectra as well as the excitation random walk model on measured fluorescence lifetimes, the radiation trapping and concentration quenching effects have been discussed. Considering all the spectroscopic and laser performance parameters, an optimum Yb-ion doping concentration (YT1) has been determined, and the gain measurements performed on the sample revealed a flat gain over a broad wavelength range could be achieved even with a low (∼20%) excitation population density. A comparative study with other hosts revealed the potentiality of the present glass for ∼1 micron emission.

Time Resolved Fluorescence and Energy Transfer Analysis of Nd3+-Yb3+-Er3+ Triply-Doped Ba-Al-Metaphosphate Glasses for an Eye Safe Emission (1.54 μm)

This paper reports on the preparation and systematic analysis of energy transfer mechanisms in Nd3+–Yb3+–Er3+ co-doped new series of barium-alumino-metaphosphate glasses. The time resolved fluorescence of Nd3+ in triply doped Ba–Al-metaphosphate glasses have revealed that, Yb3+ ions could function as quite efficient bridge for an energy transfer between Nd3+ and Er3+ ions. As a result, a fourfold emission enhancement at 1.54xa0μm of Er3+ ions has been achieved through an excitation of 4F5/2 level of Nd3+ at 806xa0nm for the glass having 3xa0mol% Yb3+ with an energy transfer efficiency reaching up to 94%. Decay of donor (Nd3+) ion fluorescence has been analyzed based on theoretical models such as direct energy transfer model (Inokuti–Hirayama) and migration assisted energy transfer models (Burshtein’s hopping and Yokota–Tanimoto’s diffusion). The corresponding energy transfer parameters have been evaluated and discussed. Primarily, electrostatic dipole–dipole (su2009~u20096) interactions are found to be responsible for the occurrence of energy transfer process in theses glasses.

Al2O3 influence on structural, elastic, thermal properties of Yb3+ doped Ba–La-tellurite glass: Evidence of reduction in self-radiation trapping at 1 μm emission

Ba-La-tellurite glasses doped with Yb(3+) ions have been prepared through melt quenching technique by modifying their composition with the inclusion of varied concentration of Al2O3 to elucidate its effects on glass structural, elastic, thermal properties and Yb(3+) ion NIR luminescence performance. The FTIR spectral analysis indicates Al2O3 addition is promoting the conversion of BOs from NBOs which have been generated during the process of depolymerisation of main glass forming TeO4 units. The elastic properties of the glass revealed an improved rigidity of the glass network on addition of Al2O3. In concurrence to this, differential thermal analysis showed an increase in glass transition temperature with improved thermal stability factor. Also, Yb(3+) fluorescence dynamics demonstrated that, Al2O3 inclusion helps in restraining the detrimental radiation trapping of ∼1μm emission.

Network coordination in low germanium alkaline-earth gallate systems: influence on glass formation

Glass formation in a newly formulated low germanium alkaline earth gallate (LGMGa, M = Ca/Mg/Zn/Sr/Ba) system by a high temperature melt quenching route is reported here. The proportionate ratios of tetrahedral to octahedral coordination of both Ga3+ and Ge4+ network cations are found to be crucial for vitrification. The enhancement in octahedral coordination led to surface crystallization and phase separation in cast melts. This behavior has been attributed to the overall reduction in tetrahedrally coordinated network units due to the failure of Ca2+ ions in charge compensation of the [GaO4]− tetrahedron. Among different network modifying oxides, BaO in combination with CaO (mixed alkaline earth) containing compositions have proved to yield clear glass formation with improved tetrahedral networking. This has been explained though the basicity equalization concept and also due to efficient charge compensation of the [GaO4]− tetrahedron requiring lower field strength cations like Ba2+. The effective phonon energy of this low germanium calcium barium gallate (LGCBGa) glass is found to be around 650 cm−1, with an extended infrared transparency up to around 7 μm, which is superior to most of the low phonon energy oxide glass systems, making it promising for photonic and mid-infrared luminescence applications. Furthermore, the observed dark yellow to brown coloration in the glass has been attributed to the precipitation of metallic nanoparticles, and this mechanism has been discussed in detail.