CdS quantum dots (QDs) embedded in a phosphate glass matrix were investigated. The time-resolved Z-scan technique was used to determine the nonlinear refraction and absorption for different concentrations of CdS QDs. The results indicate that the nonlinear absorption presents a reverse saturable character, which is a desirable feature in the design of optical limiting devices. In addition, strong experimental evidence that the main contribution onto the refractive index variation is not of thermal origin was found. The observed variation presents a character similar to an electronic-like effect. These evidences are supported by numerical simulations.
The aim of this work is the use of the Z-scan technique to determine the nonlinear refraction and nonlinear absorption of phosphate glass doped with CdS. This glass matrix, termed as PANK (P2O5-Al2O3-Na2O-K2O), was doped with 1, 2 and 3 % of CdS concentration. The quantum dots (QDs) are materials extensively investigated in the last years for their special physical properties associated to discrete energetic levels.
In this work, we have used a Ti3+:Safira laser tuned at 803nm to performed time-resolved measurements using the Z-scan technique to characterize the nonlinear optical properties of phosphate glasses. The glass matrices, labeled PAN (P2O5-Al2O3-Na2CO3) and PANK (P2O5-Al2O3- Na2O-K2O), were doped with increasing Nd3+ concentration, ranging from 0.5 to 5 wt%. For both systems, we have seen that the optical nonlinearity has a linear dependence with the doping ion concentration. Therefore, we propose a new approach to obtain the parameters Δα and Δσ. All results obtained are in good agreement with others found in the literature.
In this work optical spectroscopic characterization was performed in a Er-doped phosphate glass matrix PAN (P2O5-Al2O3-Na2CO3). Due to its high phonon energy, only the 1550 nm emission band was observed. Therefore, we have applied the normalized lifetime thermal lens technique in order to determine the luminescence quantum efficiency of this emission. These results were compared with that obtained with the standard Judd-Ofelt calculations. Besides absorption spectra, emission spectra as also obtained. Therefore, the gain coefficient spectra could be evaluated for different population inversions. Finally, figures of merit for the optical amplifiers were estimated and compared with others Er-doped materials.
The spectroscopic properties of rare earth ions in many different hosts have been investigated, including surveys of Nd3+ in silicate, phosphate, fluorophosphates and fluoride glasses. Some of the thermal-optical properties of materials are influenced by temperature change, such as thermal diffusivity, specific heat and luminescence quantum efficiency. In this work the luminescence quantum efficiency of PANK: Nd3+, as a function of temperature (80- 480 K), was investigated using the normalized lifetime thermal lens technique. This system presents high quantum efficiency at low Nd3+ concentration and at ambient temperature, ~100%, which decrease as temperature increase. Below room temperature the effects are not in accord with the maximum value of η, which must be unity.
Energy transfer between CdSe/ZnS quantum dots of different sizes were studied through the Thermal Lens technique. It was possible to obtain the energy transfer efficiency and the individual luminescence quantum efficiency of systems
containing two sets of quantum dots with different sizes.
Thermal-Lens (TL) for fluorescence quantum efficiency (η) characterizations in a new phosphate glass matrix doped
with Nd3+ were performed. η studies were accomplish in function of Nd3+ concentrations (0.5-3 x 1020 ions/cm3). In addition, fluorescence quenching was studied by measuring the concentration dependence of the fluorescence lifetime. The results obtained by TL and fluorescence lifetime techniques are in good agreement, and corroborate with the theory for an energy transfer process involving a pair of ions, in which the main process occurring is cross-relaxation (CR).
The quantum dots (QDs) for use in nanobiotechnology trials should be thermodynamically stable and have
homogeneous dispersion, high radiative quantum efficiency (η), a very broad absorption spectrum, low levels of
nonspecific links to biological compounds and, most importantly, stability in aqueous media. Recently, a new class of
CdSe QDs called magic-sized quantum dots (MSQDs), with sizes from 1 to 2 nm and well-defined structures, has
attracted considerable attention because of its novel physical properties. The present work reports the thermo-optical
properties of CdSe/CdS MSQDs and CdSe/ZnS QDs suspended in aqueous solutions. Absolute nonradiative quantum
efficiency (φ) and η values were determined applying two techniques: the well-known Thermal Lens (TL) technique
and an alternative method called thermal spatial self-phase modulation (TSPM) technique.