Polymer composite random lasers based on diatom frustules as scatterers

Abstract

In this work the possibility to exploit the ability of multiple scattering and localization of light shown by diatom silica shells (frustules) for photoluminescence amplification in a random laser was investigated. To this aim polymethylmethacrylate matrix composite random lasers based on rhodamine B and frustules as gain medium and scatterers, respectively, were prepared by solvent casting. Two different kinds of frustules were used, the first represented by diatomite, a fossil material composed of a mixture of frustules from different diatom species, without specific shape, size and porosity; the second were living diatom frustules from freshwater biofilm, a more homogeneous biosilica, dominated by one frustule type. Chemical properties, morphology and photoluminescence of both biosilica fillers were investigated. Random laser experiments were carried out on polymer composites. The diatomite material was characterised by rectangular and circular pores, ranging from 25 nm to 1 μm in size and showed weak photoluminescence upon excitation at 405 nm. Biofilm frustules were more homogeneous in size and microstructure, with average length of about 20 μm and pore diameters between 20 and 100 nm. The frustule photoluminescence, observed after irradiation at 488, 515, 543 and 635 nm was higher than in diatomite. In addition, the two biosilica materials differed with respect to the presence of superficial silanol groups, that were not detected in diatomite. Random laser experiments showed an incoherent random lasing effect in all polymer composites. The laser threshold diminished at increasing frustule content, with a lowest value recorded using biofilm frustules (308 kW cm−2). This is probably due to the frustule size exhibited in this almost monospecific biosilica, that was in the range of most typical morphology-dependent resonators

The Diatom Staurosirella pinnata for Photoactive Material Production

“…These results indicate that the dye trapping is related to the nanostructure of frustules and to the homogeneity of the biosilica obtained from the diatom culture. It has to be noted that commercial DP has been subjected to a calcination process that could have a relevant influence on the decrease of the binding properties of organic molecules on the silica surface, such as on the absence of intrinsic photoluminescence of the DP [23]. …”

“…In our previous study frustule intrinsic photoluminescence (PL) was supposed to alter the random laser effect [23]. In order to reduce the PL effect, probably due to silanolic groups present on the surface of acid cleaned frustules, the frustules were dispersed in polyacrylamide (AA) gels and their PL assessed by means of Spectral Analysis at CLSM (SA-CLSM).…”

“…This result is not surprising, since the laser threshold is strongly correlated with the scattering properties of the matrix. In a previous paper, we showed that the addition of diatom frustules is a viable option to control the scattering properties and random lasing in a dye doped PMMA matrix [23]. PMMA is a transparent polymer that does not show scattering properties by itself.…”

“…photoanodes in dye sensitized solar cells [17], silica-titania photocatalysts for NOx abatement and air purification under UV radiation and for biomedical applications [18–20], photonic crystals for gas sensing [21] and probes for holographic optical tweezing [22]. In a previous study, we obtained the first experimental evidence of Random Laser (RL) from Rhodamine B doped polymethyl-methacrylate films filled with diatom frustules as scatterers [23]. RL is a special type of laser in which a random assembly of scattering elements dispersed into an optical gain medium replaces the optical cavity of conventional lasers.…”

“…RL is a special type of laser in which a random assembly of scattering elements dispersed into an optical gain medium replaces the optical cavity of conventional lasers. We observed an incoherent random laser effect using commercial diatomite, fossil frustules, and a mixture of frustules from extant biofilm diatoms to achieve multiple scattering of photons [23]. However, to our knowledge no studies have been published on the effect of selected and homogeneous diatom frustule typologies in RL application, though a better reproducibility of lasing performance could be achieved.…”