Debarati Ghosh

Role of Yb(3+) ions on enhanced ~2.9 μm emission from Ho(3+) ions in low phonon oxide glass system.

The foremost limitation of an oxide based crystal or glass host to demonstrate mid- infrared emissions is its high phonon energy. It is very difficult to obtain radiative mid-infrared emissions from these hosts which normally relax non-radiatively between closely spaced energy levels of dopant rare earth ions. In this study, an intense mid-infrared emission around 2.9 μm has been perceived from Ho3+ ions in Yb3+/Ho3+ co-doped oxide based tellurite glass system. This emission intensity has increased many folds upon Yb3+: 985 nm excitation compared to direct Ho3+ excitations due to efficient excited state resonant energy transfer through Yb3+: 2F5/2 → Ho3+: 5I5 levels. The effective bandwidth (FWHM) and cross-section (σem) of measured emission at 2.9 μm are assessed to be 180 nm and 9.1 × 10−21 cm2 respectively which are comparable to other crystal/glass hosts and even better than ZBLAN fluoride glass host. Hence, this Ho3+/Yb3+ co-doped oxide glass system has immense potential for the development of solid state mid-infrared laser sources operating at 2.9 μm region.

Experimental evidence for quantum cutting co-operative energy transfer process in Pr3+/Yb3+ ions co-doped fluorotellurite glass: dispute over energy transfer mechanism

Pr3+/Yb3+ doped materials have been widely reported as quantum-cutting materials in recent times. However, the question of the energy transfer mechanism in the Pr3+/Yb3+ pair in light of the quantum-cutting phenomenon still remains unanswered. In view of that, we explored a series of Pr3+/Yb3+ co-doped low phonon fluorotellurite glass systems to estimate the probability of different energy transfer mechanisms. Indeed, a novel and simple way to predict the probability of the proper energy transfer mechanism in the Pr3+/Yb3+ pair is possible by considering the donor Pr3+ ion emission intensities and the relative ratio dependence in the presence of acceptor Yb3+ ions. Moreover, the observed results are very much in accordance with other estimated results that support the quantum-cutting phenomena in Pr3+/Yb3+ pairs, such as sub-linear power dependence of Yb3+ NIR emission upon visible ∼450 nm laser excitation, integrated area of the donor Pr3+ ions visible excitation spectrum recorded by monitoring the acceptor Yb3+ ions NIR emission, and the experimentally obtained absolute quantum yield values using an integrating sphere setup. Our results give a simple way of estimating the probability of an energy transfer mechanism and the factors to be considered, particularly for the Pr3+/Yb3+ pair.

Quantum cutting induced multifold enhanced emission from Cr3+-Yb3+-Nd3+ doped zinc fluoroboro silicate glass—Role of host material

Energy transfer induced multifold enhanced emission from Yb3+ is realized in a new series of Cr3+-Yb3+ co-doped as well as Cr3+-Yb3+-Nd3+ triply doped zinc fluoroboro silicate glass system. The observed multifold enhancement of Yb3+ emission under Cr3+ excitation is attributed to probable occurrence of the quantum cutting process that is credited to the present host matrix where emission of Cr3+ is red shifted to 920 nm, which is resonant with Yb3+ absorption. The sensitized luminescence of Yb3+ in the Cr3+-Yb3+ system has further been enhanced upon inclusion of Nd3+, thus demonstrating bridging action of Nd3+ ions in this energy transfer process. The energy transfer efficiency from Cr → Yb is enhanced from 38% to 54% in the presence of Nd3+ ions. The absolute quantum yield of Yb3+ ions under Cr3+ excitation for the optimized Cr-Yb sample is found to be more than double of the Cr3+ singly doped sample and increased further in Cr-Yb-Nd doped glass confirming the contribution of quantum cutting in the energ...

Broad NIR emission near c-Si band gap from Bi-doped Ba–Al metaphosphate glasses as promising solar spectral converter

A broad and intense visible as well as NIR luminescence is obtained from bismuth ions doped in alkali-free Ba–Al metaphosphate glasses. The glasses with varied bismuth oxide content have been prepared by melt quenching technique. With increase in bismuth concentration, the NIR emitting centers are found to be dominant, while at lower concentrations no NIR emission is perceived. The visible emission covers significant portion of the visible solar spectrum, while the NIR band obtained is much blue-shifted as compared to other host matrices. FTIR reflection spectroscopy studies elucidate that the dopant bismuth plays the role of a network modifier and weaken the network by formation of NBOs and P–O–Bi bonds at the expense of [PO2] bonds. The excitation and emission spectra indicate the presence of bismuth in multiple valence state, mainly as Bi+, Bi2+, and Bi3+. The visible and NIR emissions are arising from different luminophore centers of dopant ions that are getting simultaneously excited.