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.

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.

The sensitive detection of methylene blue using silver nanodecahedra prepared through a photochemical route.

In this work, we have carried out systematic studies on the critical role of polyvinyl pyrrolidone (PVP) and citrate in the well-known chemical reduction route to synthesize silver nanodecahedra (AgND). Silver nitrate (AgNO3) was used as silver source, which can be directly converted to metallic silver after being reduced by sodium borohydride (NaBH4) under blue light-emitting diode (LED) irradiation (λ max = 465 nm), and polyvinyl pyrrolidone (PVP) as a capping agent to assist the growth of AgND. The obtained products were silver nanodecahedra of excellent uniformity and stability with high efficiency and yield. The results showed that PVP acted as a capping agent to stabilize the silver nanoparticles, prolonging the initiation time required for nanodecahedra nucleation, thus inducing anisotropic growth, allowing the size and morphology of the AgND to be controlled successfully. This improved understanding allows a consistent process for the synthesis of AgND with significantly enhanced reproducibility to be developed and the formation mechanism of these nanostructures to be elucidated. This is a simple, cost-effective and easily reproducible method for creating AgND. The typical absorption maxima in the UV-vis spectroscopy of Ag seeds was λ max ∼400 nm and that of AgND was λ max ∼480 nm. The size of the prepared AgND was in the range of 60-80 nm. SEM images confirmed the uniform and high density of AgND when the concentration of PVP was 0.5 mM. The XRD pattern showed that the final product of AgND was highly crystallized. In addition, the prepared AgND can be used to detect methylene blue (MB) in a sensitive manner with good reproducibility and stability using Surface-Enhanced Raman Scattering (SERS) phenomenon. Out of the obtained products, the AgND prepared with 50 min blue LED light irradiation (AgND-50) displayed the strongest SERS signal. Interestingly, MB in diluted solution can be detected with a concentration as low as 10-7 M (the limit of detection, LOD) and the linear dependence between SERS intensity and the MB concentration occurred in the range from 10-7 to 10-6 M. The enhancement factor (EF) of the SERS effect was about 1.602 × 106 with a MB concentration of 10-7 M using 532 nm laser excitation.