Hardy, W. H., II

Levy, P. W.

Swyler, K. J.

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To be submitted to: Optical Societyof America Topical Meeting on OpticalFiber Transmission. Williamsburg, Va.January 7-9, 1975.Jan.-!*. *»- A,The Absorption and Luminescence of GlassesDuring Electron IrradiationR. J. Swyler, W. H. Hardy, II, and P. W. LevyBrookhaven National LaboratoryUpton, New York 11973ABSTRACTAbsorption spectrum, growth and decay curves, andluminescence emission measurements have been made onNBS 710 and 711, and AO-"C" glass during and afterl.S MeV electron irradiation.iwDISTRIBUTION OF THIS DOCUMENT I'S 'jr.'LIMSTf f>^Research supported by the U. S. Atomic Energy Commission.To be submitted to: Optical Societyof America Topical Meeting on OpticalFiber Transmission. Williamsburg, Va.January 7-9, 1975.The Absorption and Luminescence of Glasses During*Electron IrradiationK. J. Swyler, W. H. Hardy, II, and P. W. LevyBrookhaven National LaboratoryUpton, New York 11973As an initial step in a program to investigate radiation effects;in materials for fiber optic, CTR and laser fusion applications, theoptical absorption and luminescence spectra of several glasses have beenmeasured during continuous electron bombardment. The measurements weremade with a recently completed computer controlled double beam recording;digital spectrometer. A sequential chopping arrangement provides simul-taneous measurement of absorption and luminescence spectra; separate256 point spectra are recorded once every 40 seconds in either the200-400 nmor 400-800na range. The absorption spectra are fully correctedfor sample and window emission, airglow, etc.The glasses studied are representative of three general types:soda-lime-silica (NBS710), lead-silica (NBS711) and high-index Ianthanide(American Optical C)• Qualitatively similar results are obtained foreach material. As shown in Fig. 1, for NBS710 glass, the irradiationinduced absorption typically covers the region from the ultraviolet"edge" to the spectrophotometer limit at 800 nm. The figure indicatesthat at least two absorption bands are present, and possibly an "edge*1shift toward lower energy. Similar results were obtained with NBS711and American Optical C glasses, although the band energies differ.Plots of the absorption coefficient (a ) vs. time (t) at photonenergies near the band maxima, show that the coloring curves areaccurately represented by an expression of the form:a(t) - (^(t) + ^ j A ^ l - e x p ^ t ) ] (1)where ct(t) is evaluated at a particular photon energy and ot̂ , A. anda. are constants. The applicability of (1) is demonstrated in Fig. 2,snowing the fit to the data points for NBS710 glass at 4 eV,In all glasses studied the absorption begins to decrease immediatelywhen the irradiation is terminated. The decreasing absorption is accu-rately described by the relation:•Research supported by the U. S. Atomic Energy Commission.-2-no(t) - Z a.exp[-d (t-t1)] t>t« (2)1-1 x *i.e. a sum of decaying exponentials with amplitude a± and decay constantd., the irradiation being terminated at time t'. Fig. 3 demonstrates thattfiis equation describes accurately the measured decay at 4 eV in NBS710glass.In contrast to our experience with alkali halides, pronouncedradiolumlnescence was not observed from the glass samples during electronbombardment* At best, only marginal luminescence was detected. Thestrong radiation induced absorption produced at all wavelengths willmarkedly attenuate, by self-absorption, any luminescence emitted withinthe sample.Several conclusions are indicated by the results obtained to date:First, the definite similarities in the absorption spectra and coloringand decay curves for the three different glasses suggest that the coloringcharacteristics may be largely controlled by a common constituent. Second,the coloring and decay are describable by equations (1) and (2), whichhave been found to apply, with one exception, to all materials studiedpreviously during irradiation in this laboratory. Third, the pronounceddecay of the absorption following irradiation indicates that the mostmeaningful radiation damage information is obtained only if measurementsare made during irradiation. Fourth, the decay occurring after irradiationprovides strong evidence that centers are both created and destroyed duringirradiation. Lastly, although only a few glasses have been examined, theseresults indicate that equipment for measuring absorption and luminescenceduring irradiation can provide a large fraction of the information requiredto determine operating characteristics of optical materials which mustfunction both during and after exposure to radiation.Fig. 1 Radiation induced absorption spectra of HBS710 glass in ths ultra-violet (upper plot) and visible (lower plot) ranges. The aeasureaents weremade both during and after 1.5 MeV electron irradiation at roos> temperature.The absorption (vertical) scale units for the upper plot are four tiaes thosefor the lower plot. The horizontal scales are photon energy and "scannumber"; tine between scans is 40 sec. or longer. A large number of scanshave been omitted. This data is subsequently used to construct absorptionspectra, growth curves at specific photon energies and other analysis "aids".3.0uI.S1.0z^o « ^ o BTIME U N UNITS OF | 0 * SECONDS 1hr hrTIME I IN UNI IS OF 10' SECONDS IFig. 2 The absorption of NBS710 glass at 3.99 eV,recorded during irradiation, at room temperature,with 1.5 KeV electrons. The beam current isapprox. SO na/cm2 (5 x 103rad/sec). The solidline through the data was computed from Eq.(1) lathe text, using one linear and two exponentialcomponents and constants determined by a computer-ised least squares procedure.Fig. 3 The decay of the radiation induced absorp-tion at 3.99 eV in NBS710 glass recorded, withoutinterrupting the measurements, after the electronbombardment was terminated. The solid linethrough the data was computed from Eq.(2) in thetext, using three decay coaponentc and constantsdetermined with a computerized least squareaprocedure.

Absorption and luminescence of glasses during electron irradiation

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Absorption and luminescence of glasses during electron irradiation

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