R. Acevesª*, R. Pérez–Salasª, T.M. Pitersª, C. Vargas–Aburtob and R.M. Uribeb
ª Centro de Investigación en Física, Universidad de Sonora, Apartado Postal 5–88, Hermosillo, Sonora, 83190 México, e–mail: raceves@cajeme.cifus.uson.mx, rperez@cajeme.cifus.uson.mx, piters@cajeme.cifus.uson.mx
b Program on Electron Beam Technology, Kent State University, 15825 Old State Road, Middlefield, OH 44062, USA, e–mail: cvargas@kutztown.edu, ruribe@kent.edu
*. Corresponding author:
e–mail: raceves@cajeme.cifus.uson.mx,
Phone: +52 662 259 2156, Fax: +52 662 212 6649.
Recibido el 12 de octubre de 2007
Aceptado el 9 de agosto de 2008
Abstract
Radiation effects of high energy electrons on pure and additively colored (AC) KCl and KBr crystals have been studied by optical absorption in the 200–800 nm range at RT. Besides the main F–center related absorption band at 553 nm, the F+2 (670 nm) and F2 (740 nm) bands (R1 and R2 centers in old notation) ascribed to F centers aggregates in additively colored KCl are clearly observed. After electron irradiation with energy of 1.0 Me V and doses of 100 kGy or 3.5 Me V and 180 kGy, the F+2 and F2 bands are strongly diminished, the intensity of the F bands is increased and its peak lightly shifted to low energy at 558 nm. In KBr, the related absorption band maximum for the pure and AC samples after irradiation shows the same peak position as the F–center absorption. For AC KBr the intensity of this peak versus accumulative doses shows a maximum around 300 kGy but in pure KBr the peak continuously increases. In contrast, KCl does not show such dependence on accumulative doses. For both samples, the electron irradiation induce at least two bands in the 210–300 nm (UV bands) range that has been related with hole centers (V bands). The results have been analyzed in terms of surface close F centers and alkali and halogen ions desorption processes.
Keywords: Electron irradiation; radiation damage; alkali halides; color centers; F centers.
Resumen
Efectos por irradiación con electrones de alta energía en cristales puros y coloreados aditivamente (CA) de KCl y KBr se han estudiado a temperatura ambiente por absorción óptica en el rango 200–800 nm. En cristales de KCl aditivamente coloreados, además de la banda de absorción más importante, en 553 nm asignada a centros F, también se observan las bandas F+2 (670 nm) y F2 (740 nm) adscritas a agregados de centros F (centros R1 y R2 en la vieja notacion). Después de la irradiación con electrones con energía de 1.0 MeV y dosis de 100 kGy ó 3.5 MeV y 180 kGy, la intensidad de las bandas F+2y F2 disminuye fuertemente y a la vez la intensidad de la banda F incrementa y su posicion se desplaza ligeramente en dirección de menor energía, a 558 nm. En KBr, despues de la irradiación, el máximo de la bandas de absorción para los cristales puros y CA muestran la misma posición de pico que la banda de absorción relacionada con el centro F. Para cristales de KBr CA la intensidad de este pico versus dosis acumulada, muestra un máximo alrededor de 300 kGy pero en cristales puros de KBr el máximo de la banda continuamente incrementa. En contraste, KCl no muestra tal dependencia sobre la dosis acumulada. Para ambas muestras la irradiación con electrones induce al menos dos bandas en el rango 210–300 nm (UV bands) que han sido relacionadas con centros de hoyo (bandas V). Los resultados se han analizado en términos de centros F cercanos a la superficie y procesos de desorción de iones alcalinos y halogenos.
]]> Descriptores: Irradiación con electrones; daños por radiación; halogenuros alcalinos; centros de color; centros F.
PACS: 61.72.jn; 61.80.Fe; 78.55.Fv
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Acknowledgments
We are thankful to M. Atondo for preparing additive colored samples. We are grateful to Mr. Jack Juras and Mr. Thomas Goodner for their technical assistance with the operation of the electron accelerator. We also wish to thank Dr. Francisco Brown–Bojorquez his support for SEM images. This work is partially support by P/ CONACyT 2002–C00–40497 (México) and P/PIFI 3.3 (P/CA–51 2006–26–18, Universidad de Sonora, México).
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