Raman Scattering and Photoluminescence of Pristine and Ion Implanted Langmuir-Blodgett Polydiacetylene Thin Films

<jats:title>Abstract</jats:title><jats:p>Fundamental optical properties of Langmuir-Blodgett polydiacetylene (LB PDA) ultra thin films are investigated. The LB films exhibit a strong absorption peak at about 16000 cm<jats:sup>-1</jats:sup> and a weak and broad peak at about 17500 cm<jats:sup>-1</jats:sup>; the color of the film is blue. After annealing at 90°C, a blue shift of the absorption peaks is observed; that is, the color of the LB films changes from blue to red. The phase transition corresponding to the color change is studied using Raman spectroscopy as a function of annealing temperature. For annealing temperatures between 50 and 60°C, the results show significant change in the ratio of Raman line intensities due to C≡C and C=C stretch modes. Such a transition is also observed for laser annealed LB PDA films. Furthermore, the photoluminescence (PL) properties of pristine (blue), annealed (red) and ion implanted (red) LB PDA films are investigated. The photoluminescence of both pristine and annealed LB PDA films show sharp peaks at about 15500 cm<jats:sup>-1</jats:sup>. The annealed LB PDA films have an additional small peak or shoulder at about 18000 cm<jats:sup>-1</jats:sup>. The photoluminescence peaks of red films implanted with 200keV As<jats:sup>+</jats:sup> ions are observed at about 16000 cm<jats:sup>-1</jats:sup> and become broad with increasing ion implantation dose in the range 10<jats:sup>12</jats:sup>–10<jats:sup>15</jats:sup> cm<jats:sup>-2</jats:sup>.</jats:p>