NaGdF4:Dy3+ nanocrystals: new insights into optical properties and energy transfer processes.

NaGdF4:Dy3+ nanocrystals (NCs) have been synthesized using a precipitation technique. The structural characteristics and morphology of the materials were analyzed using X-ray diffraction patterns and scanning electron microscopy images, respectively. The photoluminescence excitation spectra, emission spectra and decay curves of all samples were recorded at room temperature. The color feature of Dy3+ luminescence was estimated using CIE chromaticity coordinates and the correlated color temperature. The radiative properties of the Dy3+:4F9/2 level in the material were analyzed within the framework of JO theory. In NaGdF4:Dy3+ NCs, the energy transfer from Gd3+ to Dy3+ causes an enhancement in the luminescence of the Dy3+ ions. The rate of the processes taking part in the depopulation of Gd3+ ions was estimated. The energy transfer between Dy3+ ions leads to the luminescence quenching of NaGdF4:Dy3+. In this process, the dipole-dipole interaction, which is found by using the Inokuti-Hirayama model, is the dominant mechanism. The characteristic parameters of the energy transfer processes between Dy3+ ions have also been calculated in detail.

NaGdF4:Eu3+ nanocrystalline: an in-depth study of energy transfer processes and Judd-Ofelt analysis using the luminescence excitation spectrum.

NaGdF4 nanocrystalline doped with different concentrations of Eu3+ ions were synthesized using the precipitation method. The structure and morphology of the material were investigated through the measurements of the XRD patterns and SEM images, respectively. The optical properties of the NaGdF4:Eu3+ nanocrystalline were studied in the framework of the Judd-Ofelt theory in which the Ωλ parameters were calculated by two methods: the traditional method using the luminescence spectra and the self-referenced method using the luminescence excitation spectra. In NaGdF4:Eu3+ nanocrystalline, the Gd3+ ions in the lattice act as sensitizer centers for the luminescence of Eu3+ ions under excitation at 272 and 310 nm. The energy transfer process from Gd3+ to Eu3+ causes the emission enhancement of Eu3+ ions. Upon excitation by the characteristic wavelengths of Gd3+, the luminescence efficiency of the Eu3+ ions in NaGdF4:Eu3+ is affected by two mechanisms: the emission of Gd3+ ions and the trapping of excited energy by the Eu3+ ions. The energy transfer between Eu3+ ions was also discussed in detail. This process leads to the enhancement of the luminescence bands originating from the 5D0 level. The dominant interaction between the Eu3+ ions in the energy transfer process is the dipole-dipole mechanism, which is determined by fitting the decay curve of the 5D2 level to the Inokuti-Hirayama model.

Optical properties and energy transfer in KYF4:Sm3+ and KYF4:Tb3+,Sm3+ polycrystalline materials.

KYF4 polycrystalline materials singly doped with Sm3+ ions and co-doped with Tb3+/Sm3+ ions were synthesized by the hydrothermal technique. The optical spectra of all samples were measured at room temperature. The features of the ligand field and the optical properties of Sm3+ ions in KYF4 were studied via Judd-Ofelt theory. A three-level model was used to estimate the validity of the Judd-Ofelt analysis for KYF4:Sm3+. The luminescence quenching of KYF4:Sm3+ relates to energy transfer through cross relaxation between Sm3+ ions. For KYF4:Tb3+,Sm3+, the luminescence of Sm3+ ions is enhanced due to the energy transfer process from Tb3+ to Sm3+. The chromaticity features of the luminescence from KYF4:Tb3+,Sm3+ were estimated by the chromaticity coordinates and correlated color temperature (CCT). The dominant interaction mechanism and the energy transfer parameters for the Sm3+-Sm3+ and Tb3+-Sm3+ energy transfer processes were analyzed by using the Inokuti-Hirayama model.

Tunable luminescent emission characterization of type-I and type-II systems in CdS-ZnSe core-shell nanoparticles: Raman and photoluminescence study.

We used wet chemical methods to synthesize core-shell nanocrystalline samples CdS(d)/ZnSe N , where d = 3-6 nm and N = 1-5 are the size of CdS cores and the number of monolayers grown on the cores, respectively. By annealing typical CdS(d)/ZnSe N samples (with d = 3 and 6 nm and N = 2) at 300 °C for various times t an = 10-600 min, we created an intermediate layer composed of Zn1-x Cd x Se and Cd1-x Zn x S alloys with various thicknesses. The formation of core-shell structures and intermediate layers was monitored by Raman scattering and UV-vis absorption spectrometers. Careful photoluminescence studies revealed that the as-prepared CdS(d)/ZnSe N samples with d = 5 nm and N = 2-4, and the annealed samples CdS(3 nm)/ZnSe2 with t an ≤ 60 min and CdS(6 nm)/ZnSe2 with t an ≤ 180 min, show the emission characteristics of type-II systems. Meanwhile, the other samples show the emission characteristics of type-I systems. These results prove that the partial separation of photoexcited carriers between the core and shell is dependent strongly on the engineered core-shell nanostructures, meaning the sizes of the core, shell, and intermediate layers. With the tunable luminescence properties, CdS-ZnSe-based core-shell materials are considered as promising candidates for multiple-exciton generation and single-photon sources.

Thermoluminescence properties and new insights on the UV-vis absorption features of colorless quartz after γ-ray irradiation.

In this paper, we present the results of research on the thermoluminescence (TL) and optical absorption (OA) properties of colorless natural quartz (including natural quartz samples, sodium ion (Na+) rich samples (by diffusion), and alkali metal (M+) ion poor samples (by sweep)). In detail, the relationship between the TL glow peaks and the emission wavelength was determined. The dynamics parameters (E T, s, τ) have been computed for all TL peaks on the glow curve. The recombination mechanism electron-hole with the participation of the region energy has been determined for all electron traps in the temperature range of 50-430 °C through thermally stimulated conductivity measurement (TSC). Nonlinearity and approaching signal saturation are observed at doses above 22 Gy for the electron trap at 110 °C, above 45 Gy for the electron trap at 238 °C, and 80 Gy for the electron traps at 325 °C and 375 °C. The role of irradiation and heat treatment in the formation of absorption centers as well as the relationship of these centers to electronic traps have been also investigated in detail. The role of M+ ions and hydrogen ions (H+) for the absorption bands in the UV-vis region has been discussed. The results of the combination of the TL measurement and monochromatic light absorption according to temperature show that the TL process occurs concurrently with the reduction of the absorbent center produced in the irradiation process.

Evaluation of diffusion coefficient of P-glycoprotein molecules labeled with green fluorescent protein in living cell membrane.

The movement of individual molecules inside living cells has recently been resolved by single particles tracking (SPT) method which is a powerful tool for probing the organization and dynamics of the plasma membrane constituents. Effective treatment of metastatic cancers requires the toxic chemotherapy, however this therapy leads to the multidrug resistance phenomenon of the cancer cells, in which the cancer cells resist simultaneously to different drugs with different targets and chemical structures. P-glycoprotein molecules which are responsible for multidrug resistance of many cancer cells have been studied by cancer biologists during past haft of century. Recently, advances in laser and detector technologies have enabled single fluorophores to be visualized in aqueous solution. The development of the total internal reflection fluorescent microscope (TIRFM) provided means to monitor dynamic molecular localization in living cells. In this paper, P-glycoproteins (PGP) were labeled with green fluorescent protein (GFP) in living cell membrane of Madin-Darby canine kidney (MDCK) and the TIRFM method was used to characterize the dynamics of individual protein molecules on the surface of living cells. An evanescent field was produced by a totally internally reflected and a laser beam was illuminated the glass-water interface. GFP-PGP proteins that entered the evanescent field appeared as individual spots of light which were slighter than background fluorescence. We obtained high-resolution images and diffusion maps of membrane proteins on cell surface and showed the local diffusion properties of specific proteins on single cells. We also determined the diffusion coefficient, the mean square displacement and the average velocity of the tracked particles, as well as the heterogeneity of the cell environment. This study enabled us to understand single-molecule features in living cell and measure the diffusion kinetics of membrane-bound molecules.

Tunable LSPR of silver/gold bimetallic nanoframes and their SERS activity for methyl red detection.

Ag/Au bimetallic nanostructures have received much attention in surface-enhanced Raman scattering (SERS). However, the synthesis of this nanostructure type still remains a challenge. In the present research, Ag/Au nanoframes were synthesized via a simple room temperature solution phase chemical reduction method using pre-synthesized triangular Ag nanoplates as templates in the presence of appropriate amounts of HAuCl4. Controlling experimental parameters was applied for understanding of the growth mechanism. The galvanic exchange reaction resulted in a uniform deposition of the Au shell on the Ag nanoplates and the Ag core was removed which generated triangular hollow nanoframes. It is found that the amount of HAuCl4 added to the growth solution played a key role in controlling the Ag/Au nanoframes. The resultant silver/gold nanoframes with average size of 50 nm were applied in detecting methyl red (MR) in the solution-phase using an excitation wavelength laser of 532 nm. The SERS signal was greatly enhanced owing to the tunable plasmonic peaks in the visible region (400-650 nm). The limit of detection (LOD) of MR in diluted solution was 10-6 M. The enhancement factor (EF) was about 8 × 104 toward 10-5 M of MR. Interestingly, the linear dependence between the logarithm of the SERS signal intensity (log I) and the logarithm of the MR concentration (log C) occurred in the range from 10-6 to 10-4 M. Our work promises the application of Ag/Au nanoframes as a chemical sensor in detecting MR molecules at low concentration with high performance.

The structural transition of bimetallic Ag-Au from core/shell to alloy and SERS application.

It is well-known that Ag-Au bimetallic nanoplates have attracted significant research interest due to their unique plasmonic properties and surface-enhanced Raman scattering (SERS). In recent years, there have been many studies on the fabrication of bimetallic nanostructures. However, controlling the shape, size, and structure of bimetallic nanostructures still has many challenges. In this work, we present the results of the synthesis of silver nanoplates (Ag NPls), and Ag-Au bimetallic core/shell and alloy nanostructures, using seed-mediated growth under green LED excitation and a gold salt (HAuCl4) as a precursor of gold. The results show that the optical properties and crystal structure strongly depend on the amount of added gold salt. Interestingly, when the amount of gold(x) in the sample was less than 0.6 µmol (x < 0.6 µmol), the structural nature of Ag-Au was core/shell, in contrast x > 0.6 µmol gave the alloy structure. The morphology of the obtained nanostructures was investigated using the field emission scanning electron microscopy (FESEM) technique. The UV-Vis extinction spectra of Ag-Au nanostructures showed localized surface plasmon resonance (LSPR) bands in the spectral range of 402-627 nm which changed from two peaks to one peak as the amount of gold increased. Ag-Au core/shell and alloy nanostructures were utilized as surface enhanced Raman scattering (SERS) substrates to detect methylene blue (MB) (10-7 M concentration). Our experimental observations indicated that the highest enhancement factor (EF) of about 1.2 × 107 was obtained with Ag-Au alloy. Our detailed investigations revealed that the Ag-Au alloy exhibited significant EF compared to pure metal Ag and Ag-Au core/shell nanostructures. Moreover, the analysis of the data revealed a linear dependence between the logarithm of concentration (log C) and the logarithm of SERS signal intensity (log I) in the range of 10-7-10-4 M with a correlation coefficient (R 2) of 0.994. This research helps us understand better the SERS mechanism and the application of Raman spectroscopy on a bimetallic surface.