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Studies of Redox Active Silicalite-2 and the Development of Stable White-Light Phosphors

Title: Studies of Redox Active Silicalite-2 and the Development of Stable White-Light Phosphors.
Name(s): Lita, Adrian, 1976-, author
Stiegman, Albert E., professor directing dissertation
Chiorescu, Irinel, university representative
Strouse, Geoffrey, committee member
Dorsey, John, committee member
Department of Chemistry and Biochemistry, degree granting department
Florida State University, degree granting institution
Type of Resource: text
Genre: Text
Issuance: monographic
Date Issued: 2009
Publisher: Florida State University
Place of Publication: Tallahassee, Florida
Physical Form: computer
online resource
Extent: 1 online resource
Language(s): English
Abstract/Description: Mn-silicalite-2 was synthesized at high pH using the molecular cluster, Mn12O12(O2CCH3)16 as a Mn Source. No precipitation of manganese hydroxide was observed with this cluster even with the use of tetrabutylammonium hydroxide as a templating agent. This synthetic approach resulted in the incorporation of up to 2.5 mol % Mn into the silicalite-2 with direct substitution into the framework verified by a linear relationship between unit cell volume and loading. The Mn is reduced to Mn(II) during hydrothermal synthesis and incorporated into the silicalite-2 framework during calcination at 500 °C. Further calcination at 750 °C does not affect the crystallinity but oxidizes essentially all of the Mn(II) to Mn(III). Cr(IV) substituted silicalite-2 was generated by reduction of Cr(VI)-silicalite-2 lattice sites at in a CO atmosphere. The reduction process, Reduction at high pressures was found to give almost complete conversion of the Cr(VI) sites to Cr(IV). As generated, the Cr(IV) sites do not reoxidize to Cr(VI) under ambient conditions or in the presence of oxidants under reaction conditions. We report the development of new class solid-state white-light phosphors based on stable nanoparticle-silica glass composites. These materials are made from the incorporating of CdSe nanoparticles into a silica Sol-gel solution. Once it gelled and aged the materials are calcined at 500 °C under oxygen. The solid that results are robust with a bright white luminescence (20%) under UV excitation that gives virtually pure white light with coordinates of (0.34, 0.36) on the CIE 1931 chromaticity diagram and, more importantly, the emission envelope coincides nearly identically with the scotopic eye response function. The white-light phosphors have a scotopic/phtopic ratio of 2.56, indicating that these phosphors will be perceived as a particularly efficient illumination source in a dark environment thereby being more energy efficient. The emission comes from a distribution of nanoscale CdSe particles, with size-polydispersity brought on by calcination and subsequent fusing of nanoparticle agglomerates in the micropores of the silica xerogel. The silica matrix makes them exceedingly robust, with no changes in the emission properties observed for periods in excess of 18 months.
Identifier: FSU_migr_etd-1199 (IID)
Submitted Note: A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Degree Awarded: Fall Semester, 2009.
Date of Defense: October 28, 2009.
Keywords: Zeolite, Transition metal, Vibronic structure, LED, White-light, Nanoparticles
Bibliography Note: Includes bibliographical references.
Advisory Committee: Albert E. Stiegman, Professor Directing Dissertation; Irinel Chiorescu, University Representative; Geoffrey Strouse, Committee Member; John Dorsey, Committee Member.
Subject(s): Chemistry
Persistent Link to This Record:
Owner Institution: FSU

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Lita, A. (2009). Studies of Redox Active Silicalite-2 and the Development of Stable White-Light Phosphors. Retrieved from