Djalmir N. Messias

Energy transfer upconversion determination by thermal-lens and Z-scan techniques in Nd 3+ -doped laser materials

The Z-scan and thermal-lens techniques have been used to obtain the energy transfer upconversion parameter in Nd3+-doped materials. A comparison between these methods is done, showing that they are independent and provide similar results. Moreover, the advantages and applicability of each one are also discussed. The results point to these approaches as valuable alternative methods because of their sensitivity, which allows measurements to be performed in a pump-power regime without causing damage to the investigated material.

Nd:YAG optical electronic nonlinearity and energy transfer upconversion studied by the Z-scan technique

A procedure to obtain the Energy Transfer Upconversion parameter, γ, for Nd3+:YAG by using the Z-scan technique is presented in this paper. It was found γ = (2.0 ± 0.3) × 10−16 cm3/s, from the open aperture transmittance. Also obtained was the nonlinear refractive index, the polarizability difference and absorption cross-section difference between excited and ground state at 808.7 nm.

Study of the nonlinear optical properties of CdS quantum dots in phosphate glass

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.

Optical characterization of core–shell quantum dots embedded in synthetic saliva: Temporal dynamics

The present work reports the spectroscopic and thermo-optical properties of CdSe/ZnS and CdSe/CdS core-shell quantum dots (QDs) embedded in synthetic saliva. Spectroscopy studies were performed applying nonfunctionalized CdSe/ZnS QDs (3.4, 3.9 and 5.1 nm cores) and hydroxyl group-functionalized ultrasmall CdSe/CdS core-shell quantum dots (1.6 nm core) suspended in artificial saliva at different potential of hydrogen (pH) values. Saliva was chosen because it is important in a variety of functions such as protecting teeth through the buffering capacity of the formed biofilm, hydration, and dental remineralization. Thermo-optical characterizations using the thermal lens (TL) technique were performed in QD-biofluids for different QD sizes and pH values (3.9-8.3) of the synthetic oral fluids. Transient TL measurements were applied to determine the fluorescence quantum efficiency (η) in QD-biomaterial systems. High η value was obtained for ultrasmall CdSe/CdS QDs. Fluorescence spectral measurements of the biomaterials support the TL results. In addition, for nonfunctionalized (3.4 and 5.1 nm) and hydroxyl group-functionalized QDs, the temporal behavior of the fluorescence spectra was accomplished about approximately 1200 h at two different biofluid pH values (3.9 and 8.3). The temporal fluorescence intensity result is dependent on the pH of the saliva in which the QDs were embedded, QD functionalization and QD sizes. The time for an approximately 50% decrease in the peak intensity fluorescence of CdSe/ZnS QDs (3.4 nm core) and ultrasmall CdSe/CdS QDs is respectively 25 h and 312 h at pH 3.9 and 48 h and 360 h at pH 8.3.

Study of the thermal-optics parameters of Nd3+-doped phosphate glass as a function of temperature

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.

Determination of nonlinear optical properties by time resolved Z-scan in Nd-doped phosphate glass

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.

Spectroscopic and photothermal characterization Er-doped phosphate glass

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.

Energy transfer in mixtures of quantum dots of different sizes studied by thermal lens technique

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.

Study of energy transfer upconvertion process on phosphate glass through z-scan technique

In this work, we have studied the energy transfer upconversion process in phosphate glass matrix using the z-scan technique, in Nd-doped samples.

Concentration dependence of fluorescence resonance energy transfer in CdSe/ZnS quantum dots colloidal systems

Energy transfer in a CdSe quantum dot system was studied by measuring the photon migration and its spatial dependence. Signature of Forster resonance energy transfer was observed as a function of quantum dot concentration.