Photoluminescence Investigations of Cubic Boron Nitride Doped with Neodymium during High-Pressure Synthesis

International audienceMicropowders of cubic boron nitride doped with neodymium are prepared under high-pressure and high-temperature conditions. The phase composition of the micropowders is studied using X-ray diffractometry and X-ray fluorescence analysis. The photoluminescence, photoluminescence excitation spectra, and the life-time of the 4F3/2 excited state of Nd ions introduced into cubic boron nitride are investigated. In photoluminescence spectra of the micropowders, structured bands are recorded in the range of the 4F3/2→4I9/2 and 4F3/2 4I11/2 electronic transitions. A higher intensity of the first structured band indicates that the corresponding photoluminescence in cubic boron nitride doped with neodymium is excited by the “three-level scheme.” It is demonstrated that an increase in the concentration of the neodymium compound in the growth batch leads to the formation of two luminescence centers Nd1 and Nd2 formed by neodymium ions located in different low-symmetry crystal fields in the micropowders. This is confirmed by X-ray diffraction investigations and the study of the photoluminescence decay curves. The 4F3/2 short-lived state is assigned to the Nd ions forming the Nd1 centers, and the long-lived state is attributed to the Nd ions forming the Nd2 centers

Multifunctionality of nitrogen oxide compounds as a basis for preparation of practically important cellulose materials

The experience of using the multifunctional character of nitrogen oxide compounds (N204, N02, N203, HN03) in cellulose chemistry and technology is summarized. The approach discussed is based on the ability of the nitrogen oxide compounds to act as multi-purpose reagents with respect to cellulose, enabling oxidation, nitrosation, nitration, hydrolytic cleavage or adduct formation to be performed on cellulose, depending on reaction conditions. It is often possible to perform simultaneously several chemical or/and structural cellulose modifications using a sole reagent in a «one-pot» process. High solubility of nitrates formed from mineral components of vegetal tissues, along with high reactivity of HN03 toward lignin that occurs together with cellulose, provide the possibility of selective extraction of radionuclides in the course of nitric acid delignification of contaminated vegetal material. In this review, examples are given of effective use of multiple functionality of nitrogen oxide compounds in the preparation of such practically important materials as totally or partially substituted cellulose acetates soluble in organic solvents, water-soluble polysaccharide sulphates with low degree of substitution, powder forms of cellulose hydrate and of carboxylated cellulose in both structurally disordered and microcrystalline forms, as well as in isolation of radionuclide-free cellulose and nitrolignin from contaminated agricultural residues