Photoluminescence enhancement after thermal treatment of cellulose from different sources

The use of organic materials in optics/photonics is highly attractive due to its promising applications in bioimaging, optoelectronic devices, photonic pigments, etc. However, the absence of π units in polysaccharides like cellulose or chitosan represents a disadvantage as these aromatic rings or double bonds are crucial to reduce non-radiative transitions in organic materials. To our knowledge, the mechanism to achieve photoluminescence (PL) in carbohydrate polymers without π units yet to be studied. Herein, we studied the effect of the drying of cellulose samples on PL, analyzing the effect of a thermal treatment by FTIR and UV-Vis. On one hand, the dominant wavelength of all PL spectra is at 520 nm, all samples show an increment in maximum intensity of PL between 29 and 49% and diffuse reflectance after the dehydration. A blueshift was found in the PL spectra, which was confirmed by chromaticity measurements. On the other hand, there is a relationship between the reduction of the adsorbed water and OH intermolecular stretching vibrations (FTIR) and the increment in PL, specifically in bands corresponding to the intermolecular H-bonds of O₃-H···O₅ and O₂-H···O₆. According to all data collected, an energy level diagram of cellulose samples was proposed indicating a phonon induced character of luminescence.