We investigate the effects of two-dimensional confinement on the lasing properties of a classical random laser system operating in the incoherent feedback (diffusive) regime. A suspension of 250 nm rutile (TiO2) particles in a rhodamine 6G solution was inserted into the hollow core of a photonic crystal fiber generating the first random fiber laser and a novel quasi-one-dimensional random laser geometry. A comparison with similar systems in bulk format shows that the random fiber laser presents an efficiency that is at least 2 orders of magnitude higher.

We report on the hydrothermal synthesis of the [Eu(DPA)(HDPA)(H(2)O)(2)].4H(2)O lanthanide-organic framework (where H2DPA stands for pyridine-2,6-dicarboxylic acid), its full structural characterization including single-crystal X-ray diffraction and vibrational spectroscopy studies, plus detailed investigations on the experimental and predicted (using the Sparkle/PM3 model) photophysical luminescent properties. We demonstrate that the Sparkle/PM3 model arises as a valid and efficient alternative to the simulation and prediction of the photoluminescent properties of lanthanide-organic frameworks when compared with methods traditionally used. Crystallographic investigations showed that the material is composed of neutral one-dimensional coordination polymers infinity(1)[Eu(DPA)(HDPA)(H(2)O)(2)] which are interconnected via a series of hydrogen bonding interactions involving the water molecules (both coordinated and located in the interstitial spaces of the structure). In particular, connections between bilayer arrangements of infinity(1)[Eu(DPA)(HDPA)(H(2)O)(2)] are assured by a centrosymmetric hexameric water cluster. The presence of this large number of O-H oscillators intensifies the vibronic coupling with water molecules and, as a consequence, increases the number of nonradiative decay pathways controlling the relaxation process, ultimately considerably reducing the quantum efficiency (eta = 12.7%). The intensity parameters (Omega(2), Omega(4), and Omega(6)) were first calculated by using both the X-ray and the Sparkle/PM3 structures and were then used to calculate the rates of energy transfer (W(ET)) and back-transfer (W(BT)). Intensity parameters were used to predict the radiative decay rate. The calculated quantum yield obtained from the X-ray and Sparkle/PM3 structures (both of about 12.5%) are in good agreement with the experimental value (12.0 +/- 5%). These results clearly attest for the efficacy of the theoretical models employed in all calculations and create open new interesting possibilities for the design in silico of novel and highly efficient lanthanide-organic frameworks.

Metallic nanoshells have been in evidence as multifunctional particles for optical and biomedical applications. Their surface plasmon resonance can be tuned over the electromagnetic spectrum by simply adjusting the shell thickness. Obtaining these particles, however, is a complex and time-consuming process, which involves the preparation and functionalization of silica nanoparticles, synthesis of very small metallic nanoparticles seeds, attachment of these seeds to the silica core, and, finally, growing of the shells in a solution commonly referred as K-gold. Here we present synthetic modifications that allow metallic nanoshells to be obtained in a faster and highly reproducible manner. The main improved steps include a procedure for quick preparation of 2.3 ± 0.5 nm gold particles and a faster approach to synthesize the silica cores. An investigation on the effect of the stirring speed on the shell growth showed that the optimal stirring speeds for gold and silver shells were 190 and 1500 rpm, respectively. In order to demonstrate the performance of the nanoshells fabricated by our method in a typical plasmonic application, a method to immobilize these particles on a glass slide was implemented. The immobilized nanoshells were used as substrates for the surface-enhanced Raman scattering from Nile Blue A.

Random laser action is obtained in a diffusive weakly scattering regime using an alcohol solution of rhodamine 640 with silica nanoparticles prepared by the Stöber method, with different average diameters of 49, 90, 219, and 490 nm. Particle size and concentration has proven to affect the random laser performance. It is also shown that silica nanoparticles contributes for a much slower photodegradation of the dye molecules than titania nanoparticles that has been used in the majority of the dye random lasers. This fact makes it advantageous to use silica nanoparticles for the fundamental studies of random laser, due to its increase in lifetime under pumping conditions.

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