1. Abelés F A 1950J. Phys. Rad. 11 310
2. Barnoski M K 1973Introduction to intergrated optics (Plenum Press) 127
3. Bhattacharya P K, Wagh A G, Thampi N S and Sarma N 1973Nuclear physics and solid state physics (India)16 B 254
4. Carter G and Grant W A 1966Phys. Chem. Glasses 7 94
5. Dearnaley G, Freeman J H, Nelson R S and Stephen J 1973Ion implantation, Ser. defect in crystalline solids. eds S Amelinckx, R Grevers and J Nihoul (North-Holland Pub, Amsterdam) Chapter 6, 727