Studies on characterization of blue emissive chitosan/carbazolyl biphenyl (CRB) composite films and their gamma ray irradiation mediated fluorescence quenching phenomenon

Abstract

Herein, 4,4′-bis(9H-carbazol-9-yl) biphenyl (CRB) a known PhOLED was incorporated into bioplastic chitosan films (CHCRB) resulted in blue emissive composite films with high efficiency. This work presents the interesting change in optical properties of chitosan/CRB composite films wherein an insulator material has been converted into organic semiconductor material. The doping with CRB converted the non-emissive chitosan films as excellent deep blue light emissive materials which is of prime requirement for white LED. Upon irradiation, with gamma ray (15, 25, 45 kGy), the structural and morphological changes occurred in the fabricated films evidenced by analytical, spectroscopic and mechanical studies. The chitosan films exhibited UV absorption at λmax 301 nm (UVB) for unirradiated and broad absorption band at λmax 325 nm (UVA) for irradiated CHCRB films with energy band gap ranging from 2.83 to 2.03eV. Though the unirradiated films showed high intensity deep blue emission at λmax 392 nm with QY of 35.15%, photoluminescence intensity, decreased gradually to QY of 25.26% upon gamma ray irradiation in a dose dependent manner at λmax 392 nm.The quenching of fluorescence could be attributed to the photo induced electron transfer from chitosan to CRB under high energy irradiation. Spectroscopic evidences indicated by the appearance of a new absorption band in FTIR spectra at 1228 cm−1 and a peak at 401.7eV in XPS owing to the formation of quaternary nitrogen on CRB upon electron transfer. Also, colour measurement from CIE diagram indicated the material could also be used as blue emissive material in the devices. Hence, environmentally benign bioplastic films were prepared by simple technique which exhibited both UV absorbing and blue light emissive properties. This work proposes a way to make novel emissive bioplastic films which will be useful for optoelectronic as well as sensing applications.