Hybrid gold-silica nanoparticles for plasmonic applications: A comparison study of synthesis methods for increasing gold coverage.

The current work focuses on the synthesis of hybrid nanoparticles (NPs) made of a silica core (Si NPs) coated with discrete gold nanoparticles (Au NPs), which exhibit localized surface plasmon resonance (LSPR) properties. This plasmonic effect is directly related to the nanoparticles size and arrangement. In this paper, we explore a wide range of size for the silica cores (80, 150, 400, and 600 nm) and for the gold NPs (8, 10, and 30 nm). Some rational comparison between different functionalization techniques and different synthesis methods for the Au NPs are proposed, related to the optical properties and colloidal stability in time. An optimized, robust and reliable synthesis route is established, which improves the gold density and homogeneity. The performances of these hybrid nanoparticles are evaluated in order to be used in the shape of a dense layer for pollutant detection in gas or liquids, and find numerous applications as a cheap and new optical device.

A Comparative Study of Eu3+-Doped Sillenites: Bi12SiO20 (BSO) and Bi12GeO20 (BGO).

The spectroscopic properties of Eu3+-doped Bi12SiO20 (BSO) were investigated and compared with that of Eu3+-doped Bi12GeO20 (BGO). The emission properties and the absorption spectra have been measured at 10 K as well as at 300 K (room temperature). Luminescence was detected due to the direct excitation of the 5D0 level of Eu3+, as well as through the excitation of the 5D1 level. The Judd-Ofelt theoretical framework was used to compute the radiative lifetimes (τ) and the omega parameters (Ωλ). The electric dipole transition probabilities, asymmetry ratios (R), along with the branching ratios (ß) were also determined based on the obtained experimental data. The strongest detected luminescence belongs to the 5D0 → 7F0 transition observed at 578 nm, similar to the BGO sillenite. Reasons for the major presence of the 5D0 → 7F0 emission, theoretically forbidden by the Judd-Ofelt Theory, were investigated and compared with that of the BGO sillenite. Obtained results showed that the strong 5D0 → 7F0 line is also present in Eu:BSO, indicating that this is a feature of the entire sillenite family and not just Eu:BGO.

Optical Transitions and Excited State Absorption Cross Sections of SrLaGaO4 Doped with Ho3+ Ions.

The spectroscopic properties of SrLaGaO4 (SLO) crystal doped with Ho3+ ions were studied in this work. Absorption, emission spectra and decay dynamics of excited states have been measured and discussed using the Judd-Ofelt model. Photoluminescence emissions were attributed to transitions from the excited 3D3, 5S2, 5F5, 5I6 and 5I7 multiplet manifolds. The experimental lifetimes for five excited states have been compared to the theoretical values, calculated using Judd-Ofelt theory, allowing for the determination of the multiphonon relaxation rates (WnR) of the respective states. The experimental data were approximately on a line expressed by WnR = W0 exp(-αΔE) with W0 = 0.5 × 107 s-1 and α = 2.6 × 10-3 cm. To discuss the excited state absorption (ESA) pathways, that originated from several excited levels, we used the Judd-Ofelt formalism allowing determination of the integrated cross section for ESA transitions.

Temperature dependence of Er³âº ionoluminescence and photoluminescence in Gd2O3:Bi nanopowder.

Ionoluminescence (IL) and photoluminescence (PL) of trivalent erbium ions (Er(3+)) in Gd2O3 nanopowder host activated with Bi(3+) ions has been studied in order to establish the link between changes in luminescent spectra and temperature of the sample material. IL measurements have been performed with H2 (+) 100 keV ion beam bombarding the target material for a few seconds, while PL spectra have been collected for temperatures ranging from 20 °C to 700 °C. The PL data was used as a reference in determining the temperature corresponding to IL spectra. The collected data enabled the definition of empirical formula based on the Boltzmann distribution, which allows the temperature to be determined with a maximum sensitivity of 9.7 × 10(-3) °C(-1). The analysis of the Er(3+) energy level structure in terms of tendency of the system to stay in thermal equilibrium, explained different behaviors of the line intensities. This work led to the conclusion that temperature changes during ion excitation can be easily defined with separately collected PL spectra. The final result, which is empirical formula describing dependence of fluorescence intensity ratio on temperature, raises the idea of an application of method in temperature control, during processes like ion implantation and some nuclear applications.

Blue emissions in Dy3+ doped Y4Al2O9 crystals for temperature sensing.

Temperature dependent emission spectra and decay times of trivalent dysprosium (Dy3) activated Y4Al2O9 (YAM) crystals have been studied for the first time (to our knowledge). The ratio of emission lines intensity can be used in temperature measurements, as it is not dependent on the variability of absolute intensity. The Boltzmann model was applied for modeling the temperature variation of the 4I15/2 and 4F9/2 states emissions relative intensities 455 and 481 nm, respectively. The calculated approximation gives highest sensor sensitivity of about 3×10(-3)°C-1 for the 600°C-800°C range, which allows for an expectation of usefulness of Dy3+:YAM in high-temperature luminescence thermometry. Also, the measured decay times are suitable for temperature sensing.