Spatial Heterogeneity of n-Phases Leads to Different Photophysical Properties in Quasi-Two-Dimensional Methylammonium Lead Bromide Perovskite

Newly, room temperature phosphorescence (RTP) in 2D hybrid perovskites has been proved due to the energy transfer from inorganic sheets to the conjugated organic cations harnessing the triplet states. So...

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Photophysical properties and energy transfer mechanism of a praseodymium compound with a two-dimensional layer

Journal of Chemical Research ◽

10.1177/1747519819900273 ◽

2020 ◽

Vol 44 (5-6) ◽

pp. 343-348

Author(s):

Wen-Tong Chen

Keyword(s):

Energy Transfer ◽

Solid State ◽

Hydrothermal Reaction ◽

Photophysical Properties ◽

Transfer Mechanism ◽

Energy Transfer Mechanism ◽

Two Dimensional ◽

Monoclinic System ◽

Reflectance Measurement ◽

Praseodymium Complex

A hydrothermal reaction results in the formation of a novel [Pr2(2,5-PA)2(2,5-HPA)2(H2O)4] n·2 nH2O complex (2,5-H2PA = 2,5-pyridinedicarboxylic acid). The complex is structurally characterized by single-crystal X-ray diffraction and crystallizes in the space group P21 of the monoclinic system with two formula units in one cell. This praseodymium complex is characterized by a two-dimensional layered structure. A solid-state photoluminescence experiment reveals that the praseodymium complex shows an emission in the red region. The complex has Commission Internationale de I’Éclairage chromaticity coordinates of 0.5495 and 0.4492. The photoluminescence emission bands could be assigned to the characteristic emission of the 4 f electron intrashell transition of the 3 P0 → 3 H5, 1 D2 → 3 H4, 3 P0 → 3 H6, 3 P0 → 3 F2, and 3 P1 → 3 F3 of the Pr3+ ions. The energy transfer mechanism is explained by the energy level diagrams of the praseodymium ions and the 2,5-H2PA ligand. A solid-state diffuse reflectance measurement shows that the complex possesses a wide optical band gap of 3.48 eV.

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Low-pass filtering, a new method of fractal analysis: application to PET images of pulmonary blood flow

Journal of Applied Physiology ◽

10.1152/jappl.2000.88.4.1365 ◽

2000 ◽

Vol 88 (4) ◽

pp. 1365-1373 ◽

Cited By ~ 24

Author(s):

Jose G. Venegas ◽

Gaetano G. Galletti

Keyword(s):

Spatial Heterogeneity ◽

Coefficient Of Variation ◽

Corner Frequency ◽

Pulmonary Perfusion ◽

Two Dimensional ◽

Natural Logarithm ◽

Positron Emission ◽

Functional Images ◽

Low Pass ◽

Vertical Gradients

The pattern of a spatial structure that repeats itself independently of the scale of magnification or resolution is often characterized by a fractal dimension ( D). Two-dimensional low-pass filtering, which may serve as a method to assess D, was applied to functional images of pulmonary perfusion measured by positron emission tomography. The corner frequency of a low-pass filter is inversely proportional to the resolution scale. The method was applied to three types of images: random noise images, synthetic fractal images, and positron emission tomographic images of pulmonary perfusion. Images were processed with two-dimensional low-pass filters of decreasing corner frequencies, and a spatial heterogeneity index, the coefficient of variation, was calculated for each low-pass-filtered image. The natural logarithm of the coefficient of variation scaled linearly with the natural logarithm of the resolution scale for the PET images studied (average R 2 = 0.99). D ranged from 1.25 to 1.36 for the residual distribution of pulmonary perfusion after vertical gradients were removed by linear regression. D of the same data without removal of vertical gradients ranged from 1.11 to 1.14, but the fractal plots had systematic deviations from linearity and a lower linear correlation coefficient ( R 2 = 0.96). The method includes all data in the lung field and is insensitive to the effects of misregistration. We conclude that low-pass filtering offers new insights into the interpretation of D of two-dimensional functional images as a measure of the frequency content of spatial heterogeneity.

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