Comparison of the Properties of PMMA Layers Containing an Organic Dye and CdSe Quantum Dots for Sensor Applications ^†

In recent years, fiber optic sensors have been increasingly used in a wide variety of industries. Compared to traditional electronic sensors, these sensors have numerous advantages which make them preferable to specific applications. First of all, they ensure much greater sensitivity, resolution, and dynamic range. Due to the extremely small size of the active parts, it is possible to produce sensors with very small dimensions. The matrix with the active part can be applied to the front of the optical fiber. In this case, the sensor works by using the wave reflection phenomenon (external sensors) or by covering the side surface and using the evanescent wave (internal sensors).

Layers were made of a polymethyl methacrylate (PMMA) polymer as a carrier for the active dye (methyl red) and CdSe quantum dots. The smallest quantum dots can be obtained by precipitating semiconductor crystals from a solution in a liquid. Usually, compounds of elements from groups II and IV, as well as groups III and V, are used for the production of quantum dots. By manipulating the shape and size, one can influence their properties, including the phenomenon of luminescence in a specific way needed for a given application. They are characterized by high quantum efficiency and extremely narrow bands of photoluminescence emission. Compared to standard organic dyes, they have a long fluorescence lifetime, very high stability, and good resistance to photobleaching.

Quantum dots will be synthesized using the colloidal method and then introduced into the liquid polymerization mixture, from which, after polymerization, a uniform layer should be formed. The indicator dye will be directly added to the polymerization mixture, placed in the ultrasonic bath, and deposited on the slide. The paper presents the absorption and emission spectra of the produced structures as well as optical characteristics of the produced polymers.