Search

Distributed feedback (DFB) laser sensors with active films consisting of a highly efficient and photostable perylenediimide dye (perylene orange, PDI-O) dispersed in polysytrene (PS), used as passive matrix, are reported. PDIdoped- PS DFB lasers show an excellent operational durability under ambient conditions, superior to those of previously reported DFBs used for sensing purposes. Their bulk refractive index sensing capabilities, under exposure to liquids of different refractive index, have been determined from changes in their emission wavelength. The role of the active film thickness on both, the laser and the sensing performance, has been explored. The use of a thick active film (850 nm) allows obtaining the lowest possible threshold and highest operational lifetime for this type of device although the sensor sensitivity is lower than that achievable with a thin film (160 nm). It is also shown that the inclusion of a high refractive index TiO2 layer on top of the sensor structure allows improving the sensor sensitivity by around two times. This work was supported by the Spanish Government (MINECO) and the European Community (FEDER) through grant no. MAT-2011–28167-C02. M.M-V. has been partly supported by a MINECO FPI fellowship (no. BES-2009-020747).

The fabrication and characterization of highly efficient and photostable second-order distributed feedback lasers (DFB), based on polystyrene films doped with a perylenediimide (PDI) derivative as active laser material, is reported. DFB gratings were obtained via thermal nanoimprint lithography and transferred to SiO 2 substrates by reactive ion etching. The influence of the PDI concentration on the laser performance has been investigated. The best results were obtained for the device based on the 0.5 wt% PDI-doped film, that emits at a wavelength of 571 nm, with a threshold of 2.5 μJ/pulse and a photostability halflife of around 500 min; i.e. 300000 pump pulses. The effectiveness of the DFB grating is evidenced by the decrease in threshold in two orders of magnitude with respect to the amplified spontaneous emission threshold obtained for a similar film deposited over a SiO 2 substrate without grating.

The concentration dependence of amplified spontaneous emission (ASE) in optically pumped polystyrene (PS) films containing a variable concentration (between 2.5 and 100 % by weight (wt)) of the luminescent and hole-transporting organic molecule N,N'-Bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) is studied. It is observed that the photoluminiscence (PL) efficiency, the ASE threshold and the linewidth above threshold, decrease with concentration up to 20 wt % doped films and then keeps a constant value up to concentrations of 100 wt % (neat films). The position of ASE can be tuned between 413nm and 421 nm by changing the concentration of TPD. It was also possible to tune the ASE position (between 404 and 417 nm) trough control of the film thickness (between 100 and 200 nm). The observed shifts of the ASE position due to changes in concentration are determined by the PL efficiency (not by the waveguiding characteristics of the films). On the other hand, the observed shifts in the ASE position due to changes in film thickness depend on the shape of the PL spectrum and on cut-off thickness limitations. In this case, the ASE thresholds depend on the different confinement of the propagation modes due to thickness variations.

Solar holoconcentrators based on transmission holograms as well as reflection holograms have been designed. In the first case we have shown that silver-halide gelatin, which has a light sensitivity ≈103 times better than dichromated gelatin, is an alternative. In the second case we have developed methods to make broad-band violet spectrally responsive holoconcentrators.