SYNTHESIZE OF CARBON DOTS (CDS)/PVA COMPOSITE FILM AND ITS OPTICAL PROPERTIES

• Main Author: TASPIKA (NIM: 20216012), MELDA
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/28848
• Institution: Institut Teknologi Bandung

Carbon dots (CDs) are highly studied photoluminescence material because of their merits such as simple process, low-cost raw material, eco-friendly, low toxicity, and good optical properties. However, the optical properties of CDs solution is quenched caused by rotational motion, vibration, and collisions between CDs molecules. To reduce the quenching effect, CDs solution is dispersed in poly (vinyl) alcohol (PVA) as a matrix polymer and surface passivation agent. PVA has excellent optical transparency and many hydroxyl groups. Hydroxyl groups of PVA make a hydrogen bonding with CDs surface functional groups. Hydrogen bond will protect CDs from the quenching effect. The composite layer of CDs / PVA absorb ultraviolet (UV) and Near Infra-red (NIR) simultaneously. UV absorption is caused by π→π* and n π→π* transitions, caused by the C = C aromatic bond and C = O or C-OH functional groups, respectively. NIR absorbance is caused by aromatic transition of sp2 system owned by C = O and C = N which is pyrrolic-N. UV absorption is caused by the core structure of the CDs, whereas the absorbance of NIR is caused by the surface of the CDs. The concentration of CDs dispersed into PVA is varied by 0; 0, 5; 0.8; 1, 2, 3, 4, and 5% v / v. The absorbance intensity of UV and NIR increases with with the increase of CDs concentration, according to Lambert-Beer's law for thin films. However, the optimum ratio of the maxima UV absorbance intensity to the maxima NIR absorbance is getting for 2% v / v CDs. The results of the PL measurements showed that the luminescence intensity of the film increased with the addition of CDs, then dropped after reaching the optimum for the layer with 1% v / v CDs. The decrease of photoluminescence intensity is due to the influence of inner filters, photoluminescence reabsorption, and partial quenching caused by particle agglomeration. The peak emission of the CDs / PVA composite layer is independent-excitation because of rich amino functional groups on the surface of CDs. This functional groups make the surface passivated. Consecuently, the emission of CDs is only generated by sp2 transition of carbon hybridization. The composite layer of CDs / PVA has blue-shift emission wavelength because of the hydrogen bonding between PVA and CDs. The non-radiative recombination of CDs molecules is prevented. PVA also successfully maintained the absorbance UV and NIR of composite films when the heating temperature is 200 ºC for one hour. The large number of hydrogen bonds make CDs still be protected from the quenching caused by heating. CDs/PVA composite films are stabilyze when exposed by 365 nm-UV for 6 hours, also stabilyze when exposed by visible light for 7 days. The CDs / PVA composite films are potentially used as multifunctional films for biomedicine and bioimaging.