TECH R l-C NAT L INST. Of STAND & AlllOM QblH14 iMJIJWilDinfnm i tm n TIMtTmTiT Standardization in Spectrophotometry and Luminescence Measurements Proceedings of a Workshop Seminar Held at the National Bureau of Standards Gaithersburg, Maryland, November November 19-20, 1975 Edited by: K.D. Mielenz, R.A. Velapoldi, and R. Mavrodineanu Analytical Chemistry Division Institute for Materials Research National Bureau of Standards Washington, D.C. 20234 U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary Dr. Sidney Harman, Under Secretary NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director Issued May 1977 Library of Congress Cataloging in Publication Data Workshop Seminar on Standardization in Spectrophotometry and Luminescence Measurements, National Bureau of Standards, 1975. Standardization in spectrophotometry and luminescence measure- ments. (NBS special publication ; 466) "Organized by the Analytical Chemistry Division, Institute for Materials Research, at the National Bureau of Standards." "Reprinted from the National Bureau of Standards Journal of Re- search, Section A. Physics and Chemistry, vol. 80 A, nos. 3 and 4, May- June, and July-Aug. 1976." Supt. of Docs. no. C13. 10:466 1. Spectrophotometry-Cnngresses. 2. Fluorimetry-Congresses. 3. Phosphorimetry—Congresses. I. Mielenz, K. D. II. Velapoldi, R. A. III. Mavrodineanu, Radu, 1910- IV. United States. National Bureau of Standards. Analytical Chemistry Division. V. Title. VI. Series: United States. National Bureau of Standards. Special publication ; 466. QC100.U57 no. 466 [QD79.P46] 602'. Is [543'.085] 77-4739 Library of Congress Catalog Card Number: National Bureau of Standards Special Publication 466 Nat. Bur. Stand. (U.S.), Spec. Publ. 147, 155 pages (May 1977) CODEN: XNBSAV Reprinted from the National Bureau of Standards Journal of Research, Section A. Physics and Chemistry Vol. 80A, Nos. 3 and 4, May-June, and July-Aug. 1976. U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1977 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13. 10:466). Stock No. 003-003-01791-4 - Price $5.25 (Add 25 percent additional for other than U.S. mailing). Abstract This volume contains 15 papers presented at the Workshop Seminar on Standardization in Spectrophotometry and Luminescence Measurements organized by the Analytical Chemistry Division, Institute for Materials Research, at the National Bureau of Standards, and held from November 19 to 20, 1975. These papers discuss the problems encountered where accurate measurements are required in the fields of luminescence quantum yields, diffuse reflectance spectroscopy, and ultraviolet absorption spectrometry. They also define the needs for standardization of measurements in these fields and suggest materials that could be used as Standard Reference Materials. Con- siderations on some applications of such standards in the field of environmental pollution and health are included. Key words: Accuracy; critical parameters; diffuse reflectance; fluorescence; instrumentation; luminescence; quantum yield; spectrophotometry; Standard Reference Materials; standardization. Ill Foreword A major function of the Institute for Materials Research of the National Bureau of Standards is the development of Standard Reference Materials (SRM's). These are: well characterized materials that can be used to calibrate a measurement system or to produce scientific data which can be re- ferred to a common base. In order to assure that these SRM's meet real needs and are certified to a realistic degree of accuracy, the Institute for Materials Research has sponsored a series of 'Workshop Seminars' in which leading domestic and foreign experts meet with NBS staff members to define the state of the art and to establish priorities for future efforts. The Workshop Seminar on 'Standardization in Spectrophotometry and Luminescence Measure- ments' was organized by the Analytical Chemistry Division, and was held at the National Bureau of Standards in Gaithersburg, Md., on November 19 and 20, 1975. Approximately forty participants, coming from seven different countries and representing industries, universities, as well as standard- izing laboratories, gathered to exchange ideas on improved standards and measurement techniques. Three specific topics were discussed: luminescence quantum yields, diffuse reflectance spectroscopy, and ultraviolet absorption spectrometry. The fifteen papers given represented the points of view of chemists and physicists using these techniques for widely different applications: analytical and clini- cal chemistry, photochemistry, photometry and colorimetry, laser physics, and space research. Previous work in our Division has resulted in the development of several SRM's for spectro- photometry and luminescence spectrometry: neutral density filters for verifying the transmittance accuracy of spectrophotometers, liquid absorbance standards for the uv and visible, calibrated quartz cuvettes as pathlength standards for absorption spectrometry, and fluorescence emission standards to calibrate the spectral responsivity of luminescence spectrometers. These Proceedings will provide the basis for further progress. Philip D. LaFleur, Chief Analytical Chemistry Division January 1977 IV Preface Due to advances in optical instrumentation, electronics, and computer technology, spectrophoto- metry and luminescence measurements can now be performed with a precision that frequently ex- ceeds the accuracy of the results by a wide margin. The achievement of comparable accuracies requires improved standards as well as a better understanding of the measurement process. Thus, in organizing this Workshop Seminar on 'Standardization in Spectrophotometry and Luminescence Meas- urements' at NBS, we have endeavored to provide an interdisciplinary forum for chemists and physicists to present their views on how to achieve this goal. In this manner, we could learn from one another and, perhaps, also close the communications gap that sometimes appears to exist in these fields. The first part of these proceedings contains five invited papers on the measurement of lumines- cence yields. The introductory paper by J.B. Birks reviews the basic principles of fluorescence spec- trometry and defines the parameters to be measured. A. Bril and A.W. de Jager-Veenis discuss radiometric methods of luminescence efficiency measurements, J.N. Demas and B.H. Blumenthal describe the actinometric determination of luminescence quantum yields, and J.B. Callis illustrates the use of calorimetric techniques. In the final paper of this section, K.H. Drexhage discusses the chemistry of fluorescent dyes and proposes new fluorescence standards. In the section on diffuse reflectance spectroscopy, R.W. Frei reviews the numerous applications of this technique and H.G. Hecht summarizes the theories that are used for interpreting the results obtained. W. Budde discusses the calibration of diffuse reflectance standards, and J.B. Schutt and G.J. Buffone present practical examples of this technique in space technology and clinical chemistry. Errors in spectrophotometry and standards used to avoid them are discussed by A.G. Reule and A.R. Robertson. The suitability of potassium dichromate solutions as ultraviolet absorbance standards is demonstrated by R.W. Burke and R. Mavrodineanu. Considerations on semi-reflecting metallic films as transmittance standards are presented by R. Mavrodineanu, and the physical parameters that affect the properties of these metallic films are discussed by H.E. Bennett and J.L. Stanford. The important contributions of these authors are acknowledged with appreciation. The Workshop Seminar was planned and organized by K.D. Mielenz, R.A. Velapoldi and R. Mav- rodineanu (conference chairpersons), under the guidance of P.D. LaFleur (Chief, Analytical Chemistry Division) and J.R. DeVoe (Chief, Special Analytical Instrumentations Section), and with considerable help from R.B. Johnson, R.S. Maddox (Institute for Materials Research), S.R. Torrence (Office of Information Activities). E.S. Kershow, E.L. Zimmerman, and C.I. Wingo (Ana- lytical Chemistry Division). J.N. Demas (University of Virginia), G. Weber (University of Illinois). F. Grum and R.N. Rand (Eastman Kodak Co.) and R.W. Burke (NBS I served as conference co-chairpersons and discussion leaders. V The seminar had the encouragement of R.S. Melville ( Executive Secretary, National Institute of General Medical Sciences). NIGMS has also supported the development of advanced instrumen- tation for absorption and fluorescence spectrometry at NBS, and its use to develop and certify Standard Reference Materials for these fields. The fifteen papers reprinted in this volume were originally published in the Journal of Research of the National Bureau of Standards, 80A, 389-428 and 551-658 (1976). Special thanks are due to D.D. Wagman (Associate Editor, J. Res. NBS), W.R. Tilley, M.S. Reid, and M.V. Betizel (Office of Technical Publications) for their considerable efforts in publishing these papers. We hope that the collection of these papers in a single volume will be a worthy sequel to the Proceedings of the 1972 Conference on Accuracy in Spectrophotometry and Luminescence Meas- urements (NBS Special Publication 378, U.S. Govt. Print. Office, 1973). K. D. Mielenz R. A. Velapoldi R. Mavrodineanu January 1977 VI Contents Page Foreword iv Preface v Part 1. Luminescence Quantum Yields Fluorescence quantum yield measurements. J. B. Birks 1 Some methods of luminescence