Mn4+ non-equivalent doped fluoride phosphor towards a short fluorescence decay time for backlighting

The non-equivalent doping of Mn4+ in the red-emitting fluoride phosphors effectively shortens the fluorescence lifetime. Herein, we successfully synthesized Rb2NaInF6:Mn4+ phosphors by an ion-exchange method. The compensation mechanism of Mn4+...

Folding and Unfolding of Exogenous G-Rich Oligonucleotides in Live Cells by Fluorescence Lifetime Imaging Microscopy of o-BMVC Fluorescent Probe

Guanine-rich oligonucleotides (GROs) can self-associate to form G-quadruplex (G4) structures that have been extensively studied in vitro. To translate the G4 study from in vitro to in live cells, here fluorescence lifetime imaging microscopy (FLIM) of an o-BMVC fluorescent probe is applied to detect G4 structures and to study G4 dynamics in CL1-0 live cells. FLIM images of exogenous GROs show that the exogenous parallel G4 structures that are characterized by the o-BMVC decay times (≥2.4 ns) are detected in the lysosomes of live cells in large quantities, but the exogenous nonparallel G4 structures are hardly detected in the cytoplasm of live cells. In addition, similar results are also observed for the incubation of their single-stranded GROs. In the study of G4 formation by ssHT23 and hairpin WT22, the analyzed binary image can be used to detect very small increases in the number of o-BMVC foci (decay time ≥ 2.4 ns) in the cytoplasm of live cells. However, exogenous ssCMA can form parallel G4 structures that are able to be detected in the lysosomes of live CL1-0 cells in large quantities. Moreover, the photon counts of the o-BMVC signals (decay time ≥ 2.4 ns) that are measured in the FLIM images are used to reveal the transition of the G4 formation of ssCMA and to estimate the unfolding rate of CMA G4s with the addition of anti-CMA into live cells for the first time. Hence, FLIM images of o-BMVC fluorescence hold great promise for the study of G4 dynamics in live cells.

Static and Dynamic Optical Analysis of Micro Wrinkle Formation on a Liquid Surface

A spatially periodic voltage was used to create a dielectrophoresis induced periodic micro wrinkle deformation on the surface of a liquid film. Optical Coherence Tomography provided the equilibrium wrinkle profile at submicron accuracy. The dynamic wrinkle amplitude was derived from optical diffraction analysis during sub-millisecond wrinkle formation and decay, after abruptly increasing or reducing the voltage, respectively. The decay time constant closely followed the film thickness dependence expected for surface tension driven viscous levelling. Modelling of the system using numerical solution of the Stokes flow equations with electrostatic forcing predicted that wrinkle formation was faster than decay, in accord with observations.

Samarium doped alkaline earth halides as red-emitting scintillators and phosphors

<p>This thesis is concerned with the manufacture, spectroscopic characterisation, and radiation detection performance of three rare earth doped alkaline earth halides; these were designed for scintillation or phosphor detection of x-rays and γ-rays. The materials are transparent polycrystals of lanthanum or praseodymium stabilised cubic barium chloride ((La,Pr)₀.₁₂₅Ba₀.₈₇₅Cl₂.₁₂₅), BaCl₂ - SrCl₂ solid solutions, or single crystals of CaF₂. The primary dopant investigated was Sm²⁺ since this has a red emission in all the materials which is well matched to the spectral sensitivity of silicon photodiodes. The cubic structure of the polycrystalline materials is essential for optical transparency, and so the structural stability of the materials has been investigated using x ray diffraction and thermal analysis. For CaF₂ large single crystals were unintentionally produced without following the usual Bridgman-Stockbarger or Czochralski methods. All of the materials showed predominantly Sm²⁺ ions, and only in CaF₂ could evidence of Sm³⁺ ions also be seen. The spectroscopy of the 4f⁵5d¹ → 4f⁶ red emission, including lifetimes, and absorption of Sm²⁺ ions in all these materials is reported; a strong thermal cross over to 4f⁶ → 4f⁶ emission is observed and successfully modelled. A time correlated single photon counted system has been built to measure the scintillation decay time of these materials. The system yields decay times in excellent agreement with the literature values. The performance of the materials as scintillators is limited to varying degrees by the formation of colour centres which slow the electron-hole recombination process after x-irradiation. Ba₀.₃Sr₀.₇Cl₂:Sm was found to be a bright and fast x-ray phosphor. The integrated intensity (per x-ray half thickness of material) of the radioluminescence is ~ 30 % that of the commercial material, the scintillation lifetime is ~ 30 μs (c.f. milliseconds for Gd₂O₂S:Tb³⁺) and the imaging resolution is 6 LP/mm (c.f. 4.2 LP/mm for Gd₂O₂S:Tb³⁺). CaF₂:Sm²⁺ was shown to be a red-emitting scintillator with a decay time of ≤ 1 μs and a light output of 15,000 photons/MeV when cooled by dry ice. The x-ray imaging resolution was high at 8.5 LP/mm. Several of the materials have been tested for performance as neutron detecting phosphors by adding neutron capture elements such as gadolinium or lithium, the strongest emission observed was 6 % the integrated intensity of the standard material ⁶LiI(Eu²⁺).</p>

Samarium doped alkaline earth halides as red-emitting scintillators and phosphors

<p>This thesis is concerned with the manufacture, spectroscopic characterisation, and radiation detection performance of three rare earth doped alkaline earth halides; these were designed for scintillation or phosphor detection of x-rays and γ-rays. The materials are transparent polycrystals of lanthanum or praseodymium stabilised cubic barium chloride ((La,Pr)₀.₁₂₅Ba₀.₈₇₅Cl₂.₁₂₅), BaCl₂ - SrCl₂ solid solutions, or single crystals of CaF₂. The primary dopant investigated was Sm²⁺ since this has a red emission in all the materials which is well matched to the spectral sensitivity of silicon photodiodes. The cubic structure of the polycrystalline materials is essential for optical transparency, and so the structural stability of the materials has been investigated using x ray diffraction and thermal analysis. For CaF₂ large single crystals were unintentionally produced without following the usual Bridgman-Stockbarger or Czochralski methods. All of the materials showed predominantly Sm²⁺ ions, and only in CaF₂ could evidence of Sm³⁺ ions also be seen. The spectroscopy of the 4f⁵5d¹ → 4f⁶ red emission, including lifetimes, and absorption of Sm²⁺ ions in all these materials is reported; a strong thermal cross over to 4f⁶ → 4f⁶ emission is observed and successfully modelled. A time correlated single photon counted system has been built to measure the scintillation decay time of these materials. The system yields decay times in excellent agreement with the literature values. The performance of the materials as scintillators is limited to varying degrees by the formation of colour centres which slow the electron-hole recombination process after x-irradiation. Ba₀.₃Sr₀.₇Cl₂:Sm was found to be a bright and fast x-ray phosphor. The integrated intensity (per x-ray half thickness of material) of the radioluminescence is ~ 30 % that of the commercial material, the scintillation lifetime is ~ 30 μs (c.f. milliseconds for Gd₂O₂S:Tb³⁺) and the imaging resolution is 6 LP/mm (c.f. 4.2 LP/mm for Gd₂O₂S:Tb³⁺). CaF₂:Sm²⁺ was shown to be a red-emitting scintillator with a decay time of ≤ 1 μs and a light output of 15,000 photons/MeV when cooled by dry ice. The x-ray imaging resolution was high at 8.5 LP/mm. Several of the materials have been tested for performance as neutron detecting phosphors by adding neutron capture elements such as gadolinium or lithium, the strongest emission observed was 6 % the integrated intensity of the standard material ⁶LiI(Eu²⁺).</p>

Prediction model based on chemical composition change for the mechanical degradation of Korean pine (Pinus koraiensis) after brown-rot fungi (Gloeophyllum trabeum) invasion

In order to predict the mechanical properties of Korean pine after brown-rot decay based on its chemical composition change, 252 samples were prepared and exposed to a 14-week accelerated laboratory decay test using the brown-rot fungus Gloeophyllum trabeum. The mass loss, parallel-to-grain compressive strength, parallel-to-grain tensile strength and bending strengths were tested. Then chemical components and scanning electron micrograph analysis were conducted every two weeks. Results indicated that the mass loss rates of the samples increased with the increasing decay time and were negatively correlated with the sample volume. The strength loss rates were positively correlated with the decay time and mass loss rates. After 14 weeks the average strength loss rates of the parallel-to-grain compressive, tensile and bending samples reached 32%, 41% and 41%, respectively. Strengths degradation was found sensitive to the change of cellulose and hemicellulose contents. Further, mathematical regression models were proposed based on the content changes of the cellulose and hemicellulose to quantitatively predict the degradation of the strengths of Korean pine after brown-rot decay.

Luminescence Properties of InGaN/GaN Green Light-Emitting Diodes with Si-Doped Graded Short-Period Superlattice

The optical properties of InGaN/GaN green light-emitting diodes (LEDs) with an undoped graded short-period superlattice (GSL) and a Si-doped GSL (SiGSL) were investigated using photoluminescence (PL) and time-resolved PL spectroscopies. For comparison, an InGaN/GaN conventional LED (CLED) without the GSL structure was also grown. The SiGSL sample showed the strongest PL intensity and the largest PL peak energy because of band-filling effect and weakened quantum- confined stark effect (QCSE). PL decay time of SiGSL sample at 10 K was shorter than those of the CLED and GSL samples. This finding was attributed to the oscillator strength enhancement by the reduced QCSE due to the Coulomb screening by Si donors. In addition, the SiGSL sample exhibited the longest decay time at 300 K, which was ascribed to the reduced defect and dislocation density. These results indicate that insertion of the Si-doped GSL structure is an effective strategy for improving the optical properties in InGaN/GaN green LEDs.

Effects of size and dimension in optic relaxation in Rb vapor

We report on an experiment in which the fluorescence decay time of 5P levels of Rb atoms in a coated vapor cell exceeds several of milliseconds that many orders of magnitude longer than normal decay time of excited of rubidium atoms. This effect has been observed by using the pump laser with fixing frequency and the periodically scan the probing laser frequency of which overlap all Rb hyperfine linens of 5P-5S transition. Long time fluorescence decay take place in wide part of the spherical high quality coated cell. In cylindrical part of the cell or in uncoated cell the long time fluorescence decay was disappeared.