P. R. Biju

Spectroscopic parameters of Nd3+ ion in phosphate glasses

Abstract The optical absorption spectrum of Nd3+ ions in phosphate glasses of varying matrix environments has been recorded in the ultra violet, visible and near infrared region. From the absorption spectra, various spectroscopic parameters such as Slater-Condon (F2, F4 and F6), spin-orbit ( ξ 4ƒ ), Racah (E1, E2 and E3), nephelauxetic (β), bonding (δ) and Judd-Ofelt (J–O) ( Ω 2 , Ω 4 and Ω 6 ) intensity parameters were evaluated. Electric dipole Scd and magnetic dipole (Smd) line strengths were evaluated with the help of J–O intensity parameters. The observed and calculated oscillator strengths (ƒ) are found to be in reasonable agreement with one another. Using J–O parameters and calculated matrix U( λ ) radiative transition probabilities (A), total radiative transition probability (AT), radiative lifetime (τRAD) branching ratios (βR) and integrated absorption cross-sections for stimulated emission (σa) between the metastable 4F 3 2 and terminal 4IJ levels and terminal 4IJ levels were calculated. The analysis shows that the 4F 3 2 → 4I 11 2 has the potential for a laser transition in the four glasses studied. The results of these investigations have been confirmed by recording the fluorescence spectrum corresponding to the 4F 3 2 → 4I 11 2 transition.

Static energy transfer for Mn2+ : Pr3+ system in Phosphate glasses

Abstract The process of energy transfer from divalent manganese to trivalent praseodymium ions is studied with the help of Forster–Dexter theory. Some of the important energy transfer parameters such as transfer probability (PSA), quantum yield of energy transfer (μ), critical radius (R0) and critical concentration of the acceptor (CA) are evaluated for the energy transfer pairs Mn2+xa0:xa0Pr3+, Pr3+xa0:xa0Pr3+ in phosphate glasses. The transfer of energy from Mn2+ to Pr3+ was confirmed by recording the fluorescence decay curves of Mn2+ emission corresponding to various activator concentrations which show a non-exponential behaviour. Large values of transfer probabilities and transfer efficiencies suggest that Mn2+ ion can act as a good sensitizer to Pr3+ ion in phosphate glass.

Spectroscopic studies of Sm3+-doped phosphate glasses

Optical properties of Sm3+ ion in phosphate glassy matrices were studied. The absorption, fluorescence, excitation spectra and decay patterns were obtained at room temperature. The oscillator strengths of the transitions betweenJ manifolds were calculated using Judd-Ofelt theory and compared with the ones obtained experimentally. Various laser intensity parameters such as J-O parameters, radiative transition probabilities, lifetimes, branching ratio, and integrated absorption cross-section were evaluated. Radiative lifetimes of the excited states were determined and used to obtain nonradiative transition rates and quantum yields. Integrated intensity and dynamics of the fluorescence originating from the excited states were also studied as a function of Sm3+ concentration.

Upconversion fluorescence in Sm3+-doped zinc phosphate glassy matrix

The mechanism governing the upconversion fluorescence from the 4G5/2 level of Sm3+ ion has been investigated in zinc phosphate glass matrices under infrared (1.06u2009µm) laser excitation. This visible emission is centred at 590u2009nm and corresponds to the 4G5/2u2009→u20096H7/2 transition. The dependence of the integrated intensity on the excitation power confirms that this emission is due to the three-photon absorption process and is in agreement with the existing theory. The intensity of the upconversion fluorescence has a cubic dependence on the excitation power. An absolute upconversion efficiency of about 10−7 was obtained for the sample doped with 0.5u2009wt% Sm3+ ions. A quantitative estimate of the number of photons leaving the sample was also determined.

Sodium yttrium fluoride based upconversion nano phosphors for biosensing

In the present study, NaYF4-Yb3+/Er3+ having the composition NaYF4-18%Yb3+/2%Er3+ and NaYF4-20%Yb3+/2%Er3+ with and without the addition of PVP (polyvinyl pyrolidone) have been synthesised by a solution method using NaF, yttrium nitrate, ytterbium nitrate and erbium nitrate as precursors. Upconversion spectra of prepared nanomaterial under 980 nm laser excitation have been studied. The variation in upconversion spectra with new born calf serum and myoglobin has been studied. Myoglobin (Mb) may be helpful when used in conjunction with other cardiac markers for rapid determination of acute myocardial ischemia, especially in patients with a typical chest pain or nonspecific ECG changes. The variation of UC fluorescence with addition of Mb indicates the suitability of using NaYF4 based UC nanoparticles in cardiac marker detection. The detailed study is currently under progress.