tailieunhanh - ENCYCLOPEDIA OF MATERIALS CHARACTERIZATIONC phần 6

EXAFS cung cấp một quan điểm quy mô nguyên tử X-quang hấp thụ làm cho điên về số lượng, chủng loại, và khoảng cách của các nguyên tử lân cận ở giưa các nguyên từ. EXAFS là một phần của lĩnh vực quang phổ hấp thu X-ray & AS), trong đó một số các từ viết tắt rất nhiều. Một quang phổ hấp thụ tia X có chứa các dữ liệu EXAFS cũng như sự hấp thụ tia X gần tiến cấu trúc | PL Photoluminescence CARL COLVARD Contents Introduction Basic Principles Common Modes of Analysis and Examples Sample Requirements Quantitative Abilities Instrumentation Conclusions Introduction Luminescence refers to the emission of light by a material through any process other than blackbody radiation. The term Photoluminescence PL narrows this down to any emission of light that results from optical stimulation. Photoluminescence is apparent in everyday life for example in the brightness of white paper or shirts often treated with fluorescent whiteners to make them literally glow or in the light from the coating on a fluorescent lamp. The detection and analysis of this emission is widely used as an analytical tool due to its sensitivity simplicity and low cost. Sensitivity is one of the sưengths of the PL technique allowing very small quantities nanograms or low concentrations parts-per-trillion of material to be analyzed. Precise quantitative concentration determinations are difficult unless conditions can be carefully controlled and many applications of PL are primarily qualitative. PL is often referred to as fluorescence spectrometry or fluorometry especially when applied to molecular systems. Uses for PL are found in many fields including PL 373 environmental research pharmaceutical and food analysis forensics pesticide studies medicine biochemistry and semiconductors and materials research. PL can be used as a tool for quantification particularly for organic materials wherein the compound of interest can be dissolved in an appropriate solvent and examined either as a liquid in a cuvette or deposited onto a solid surface like silica gel alumina or filter paper. Qualitative analysis of emission spectra is used to detect the presence of trace contaminants or to monitor the progress of reactions. Molecular applications include thin-layer chromatography TLC spot analysis the detection of aromatic compounds and studies of protein structure and membranes. .