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The Luminescence of Thallium (I) Halide Complexes

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The Luminescence of Thallium (I) Halide Complexes AN ABSTRACT OT' THE THESIS Russell Everett Curtice for the Ph.D. in Inorganic Chernistry (Narne) (Degree) (Major) Date thesis is presented Novernber 14, L963 Title The Luminescence of Thallium (t) Halide Cornplexes Abstract approved Redacted for Privacy - (Ma;or professor) The fluorescence excitation and ernission spectra of KCl: TlCl, KBr:TlBr, and KI:TII solutions were rneasured in order to determine the spectral regions in which the thallous halide corn- plexes fluoresce. For each type of solution, it was found that the fluorescence ernission rnaxirnurn is dependent on the cornposition of the solution and the wavelength of the excitation radiation. The ex- citation spectra were found to parallel the absorption spectra. The nature and dissociation constants of yet unreported corrr- plex species rxrere deterrnined frorn the solubility data of Scott and Hu for KCl:TIC1 solutions and frorn the solubility data of Ku1rba for KI:TII solutions. Absorption rneasurernents were rnade so that the rnolar absorptivities could be deterrnined for each of the cornplex species. Evidence is given that in KCI solutions of concentration greater than 2. 5 M a cornplex ion of forrnula TlC14; (dissociation constant, t3; absorption rnaxirnurn, 253 rr,p) exists. Dissociation constants were also deterrnined for T1I, TIIZ, T1I3=, and T1I4= cornplex species; however, the rnolar absorptivities of these corn- plexes were not obtained. The fluorescence ernission spectra of KCl:TlCl and KBr: TlBr solutions were analyzed with the assistance of the dissociation constants of the cornplex species. The broad fluorescence band of the chloride solutions with rnaxirnurn at 44O rny was deterrnined to be due to the overlap of four syrnrnetric bands, which have a rnaxi- rnurrr of.37O, 435-440, and 450 rny. for T1*, TlCl and TICIZ-, and T1C14: respectively. For KBr:TlBr solutions, the broad fluores- cence band with rnaxirnurn at 480 rn2 is due to the overlap of three bands with a rnaxirnurn at 44O rn4, for T1Br, 475 rny for TlBr2 , and 495 rnru. for TlBr,l. The order of the fluorescence quanturn 4a yield is TICI*= > TLCI' z TlCl > Tl'and TlBr > TlBr, > TlBrn=. The fluorescence intensity of KI:T1I solutions, in contrast to the strong fluorescence of thallous chloride and thallous brornide cornplexes, is very weak. This weak fluorescence intensity rnay be due to dissipation of the energy by photochernical reactions or quenching by iodide ions. The dissociation constants of TIX complexes were used to calculate thallium-halide single bond energies by a therrnochernical cyclic process. The absorption spectrurn of thallous halide cornplexes was considered frorn the standpoint of electron transfer transitions. The absorption rnaxirnurn of these transitions is shifted toward longer wavelengths as the reducing strength increases and as the nurnber of coordinated halide ligands increases. The oscillator strengths of the transitions are approxirnately 0. 1. It is postulated that an electron is transferred frorn a halide ligand to the thallous ion. The sirnilarity of the absorption and emission spectra of thalliurn -containing potassiurn halide single crystal phosphors with that of the thallous halide cornplexes is dernonstrated; the conclusion is rnade that the spectra of the single crystal phosphors may be attri- buted to cornplex aggregates in the crystal lattice and that treatment of the spectra frorn the standpoint of electron transfer would be worthwhile. THE LUMINESCENCE OF THALLIUM (I) I{ALIDE COMPLEXES by RUSSELL EVERE TT CURTICE A THESIS subrnitted to OREGON S TATE UNIVERSITY in partial fulfillrnent of the requirernents for the degree of DOCTOR OF PHILOSOPHY June 1964 APPROVED: Redacted for Privacy Professor of Department of Chemistry In Charge of Major Redacted for Privacy Chairman of Department of Chernistry Redacted for Privacy Dean of Graduate School Date thesis is presented Novernber 14, 1963 Typed by Penny A. Self ACKNOWLEDGMENTS The author would like to express his sincere appreciation to Dr. Allen B. Scott for having suggested this investigation and for his assistance, suggestions, and comments in the preparation of this the s is . The author wishes to thank Dr. Virgil Freed for the use of the Aminco-Bowman spectr:ophotofluorometer and Dr. Cla.ra Storvick and staff not only for the use of the aforementioned instru- ment but also for their generosity and encouragement. The author would also like to express his gratitude to Mrs. Penny SeIf for the preparation of the manuscripts and to Mr. David MacEachern for the drafting work. TABLE OF CONTENTS Chapter Page INTRODUC TION I A. Review of the Lurninescence Process z B. Review of Single Crystal Phosphors of Thallium Activated Alkali Halides 5 C. Review of Thallous Halide -Alkali Ha1ide Solutions 8 D. Objectives . LZ E XPERIMENTAL PROCEDURE 13 A. Stock Solutions 13 B. AbsorptionStudies ... 13 C. Lurnine s cence Me as urernents I5 D. Calibration of the Excitation and Emission Monochrornators 17 E. Calibration of the Spectrophotofluororneter . .. 18 F. pH rneasurements ZL G. Effect of substitution of KNO3 for KCl in the thalliurn-containingsolid..... 2L EXPERIMENTAL RESULTS AND CALCULATIONS Z2 A. Absorption rneasurernents ZZ 1) KCl:TlCl solutions Zz 2) KI:TII solutions 29 B. Excitation and Ernission Spectra 36 1. GeneraL rernarks 36 2. KCl:TlCl solutions 40 3. KBr:TlBr solutions ..... 47 4. KI:T1I solutions 50 C. Analysis of the Ernission Spectra 53 D. Fluorescence quanturn yields 66 E. KNO3 containing TlCl 69 IV DISCUSSION AND CONCLUSIONS 70 A. Introduction 70 B. Cornplex forrnation and the stability of thallous halides 7L C. Therrnodynarnics of Coordinate Bond Formation . 76 TABLE OF CONTENTS Continued Chapter Page IV D. Interpretation of absorption and ernission spectra 80 I. Single Crystal Phosphors ... 80 2. Electron transfer spectra 81 3. Oscillator strengths of the electron transfer transitions 84 4. Cornparison of single crystal phosphors with solutions of the sarne cornposition. 87 E. Quenching ..... 88 V SUMMARY 89 SUGGESTIONS T'OR T'URTHER STUDY 91 BIBLIOGRAPHY 92 LIST OF FIGURES Figure Page I Absorption bands of Tl in alkali halide phosphors and aqueous alkali halide solutions . .. 9 2 Schematic diagrarn of the Arninco-Bowrnan Spectro- photofluorometer 16 3 Absorption spectrurn of KCl solutions containing TICI . z8 4 Solubility of TlI in solutions of KI z9 5 Absorption spectrurn of lZ b KI solutions 33 6 Absorption spectrurn of KI solutions containing TII 34 7 Average xenon arc flux as a function of wavelength 37 8 Diagram of the Arninco-Bowrnan spectrophotofluoro- rneter cell cornparhrrent, Top View 39 9 Excitation spectrum of KCI solutions containing TIC1. 4L 10 Ernission spectrum of KCI solutions containing TlCl , . 43 1t I'luorescence intensity as a function of the logarithrn of total Tl concentration ... 46 t2 Excitation spectrum of KBr solutions containing TIBr . 48 l3 Ernission spectrurn of KBr solutions containing TlBr 49 L4 Excitation and ernission spectra of KI solutions containing TII 5l 15 Effect of Na2S2O3 on the excitation and ernission spectrurn of a KI:TII solution . 5Z t6 Variation of emission intensity with TICIZ concen- tration 57 l7 Variation of. PtDZyn/r' with ernission wavelength for KC1: TICl solutions s9 18 Variation of ernission intensity with TlBr2 concen- tration 6z LIST OF FIGURES Continued Figure Page 19 variation of F1Fz"n/r n with ernission wavelength for KBr:TIBr solutiirn .. .. 64 ZO Kodak Panatomic-X filrn calibration curve 67 ZI Structure of ice 79 LIST OF TABLES Table Page I Concentration of aqueous solution L4 2 Sumrnary of the treatrnent of Scott and Huts Solubility data 27 3 Molar absorptivity 27 4 Solubility of thallous iodide in potassium iodide s olutions 3I Relative intensity frorn excitation rnonochrornator at constant slit width 38 Transrnittancy at point A of Figure 8 for KCl:TlCl solutions 39 Location of the observed excitation and emission , rnaxirnurn for KCI solutions containing 5.26 x 10-1 M TIC1 45 Surnmary of concentrations of complex species in KCl:TlCl and KBr:TlBr solutions 54 Ft Fry- values calculated frorn plots of F' against -'toncentration 58 TICI fL IO 'Wavelength of the emission rnaxirnurn for species present in KC1:TlC1 solutions 59 I1 Percent fluorescence due to species present in KCI: TlCl solutions 50 l- LZ Ftb ZV,- values calculated from F vs TlBr, concen- tration plots 63 13 Percent fluorescence due to species present in KBr: TlBr solutions 65 L4 Results of the photographic deterrnination of tlre radiant flux frorn KCI solutions containing 2.67 x I0-= M TICI . 67 15 Atomic and Ionic Constants 70 I L6 Ul, UZ, U3, and U1o61 for TlX cornplexes 75 LIST OF TABLES Continued Table Page L7 Standard entropy and hydration entropy ai 25oC 77 I8 Jherrnodynarnic values for the forrnation reaction of complexes 78 [tr1nro1"- 1 "] L9 Dissociation energy of the electron transfer excited state for tha llous chloride and thallous bromide cornplexe s 84 20 Oscillator strengths, tt/2, and L for thallous halide cornplexes 86 ZL Absorption and ernission peaks (rr,,,-) of thalliurn- activated halide phosphors and concentrated alkali halide:thaIlium halide solutions 87 THE LUMINESCENCE OF' TI{ALLIUM (I) I{ALIDE COMPLEXES I. INTRODUC TION In the period l9Z9 - 1933, rrlany investigators observed that if TlCl is added to aqueous solutions of KCl or to KCl rnelt, then new absorption and ernission bands, which are not characteristic of KCl itself, are observed. Because of the sirnilarity of the absorption and ernission spectrurn of KCI:Tl single crystal phosphors with that of KCl:TlCl solutions, the same rnechanism likeIy is responsible for the observed spectra. There is, however, no agreenrent as to the mechanism responsible for the lurninescence properties of each. The present investigation was undertaken, therefore, to study in detail the luminescence of potassium halide solutions con- taining the corresponding thallous halide. It is hoped that this investigation and the proposals therein will help elucidate the struc- ture and mechanisrr responsible for the lurninescence of single cry- stal KC1:T1 phosphors.
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