Laser-induced energy gap transitions in lead iodide crystals

Single crystals of the common polytype 2H of lead iodide were grown by zone melting and subjected to argon ion laser irradiation. Both time and intens ity of radiation were systematically varied to assess their effect on the m agnitude of band gap of the crystals. The band gap was determined by UV spe ctrophotometry. When the beam intensity was varied, the band gap value stea dily decreased from 2.53 to 2.02 eV, but the value drastically decreased fr om 2.53 to 1.04 eV when the irradiation time was varied. The results are ex plained in terms of changes in polycrystallinity, surface roughness, amount of absorption, and anisotropic nature of thermal conductivity of the mater ial. (C) 2001 Elsevier Science Ltd. All rights reserved.