%0 Journal Article
%T Excitation Density Dependence of Optical Oxygen Sensing in Poly(9,9-dioctylfluorene) Waveguides Showing Amplified Spontaneous Emission
%A M. Anni
%A S. Lattante
%J ISRN Materials Science
%D 2014
%R 10.1155/2014/856716
%X Reversible oxygen induced emission quenching of both the Spontaneous Emission (SE) and the Amplified Spontaneous Emission (ASE) of poly(9,9-dioctylfluorene) waveguides is demonstrated. We show that ASE shows a stronger quenching than SE, up to about 6.2 times, but also a stronger decrease when the excitation density increases. We conclude that the fast increase of the ASE decay rate is the main process in determining the ASE detection sensitivity, limiting the potentiality of sensitivity improvement of ASE with respect to SE. 1. Introduction The development of novel active systems for gas sensing is receiving increasing attention due to the very wide range of possible applications. In particular the detection of oxygen is particularly interesting in the medical field for the monitoring of oxygen content in both air and blood, as well as in the environmental monitoring field [1]. Among the different proposed techniques, exploiting the oxygen effects on the electric conductivity [2], material color [3], and chemiluminescence [4], optical sensors, based on the oxygen induced photoluminescence quenching, are characterized by fast response time and high sensitivity. The typical active systems are blends between an inert matrix and a phosphorescent molecule [5], while reversible oxygen induced fluorescent quenching in poly(9,9-dioctylfluorene) (PF8) neat films was recently demonstrated [6]. A recent breakthrough in the sensitivity enhancement was represented by the demonstration that in neat active films showing optical gain, the Amplified Spontaneous Emission (ASE) and the laser intensity show a stronger relative quenching with respect to the Spontaneous Emission (SE) [7], exploited in efficient explosive vapours detection. This first result was followed by similar demonstration [8] of explosive detection in PF8 and in few evidences of oxygen detection [9, 10]. In this letter we demonstrate reversible oxygen induced emission quenching of both the Spontaneous Emission (SE) and the Amplified Spontaneous Emission (ASE) in a PF8 waveguide. We demonstrate that the ASE shows a detection sensitivity up to 6.2 times larger than the SE and a stronger sensitivity decrease as the excitation density increases. The relaxation processes affecting the intensity quenching of both SE and ASE are discussed concluding that the fast ASE rate increase with the excitation density is the process limiting the sensitivity improvement of ASE with respect to SE. 2. Materials and Methods The PF8 film, with a thickness of about 650£¿nm, was realized by spin coating on a glass substrate
%U http://www.hindawi.com/journals/isrn.materials.science/2014/856716/