Optical Dopants Research Articles

Chemical and microstructural characterization of sol–gel coatings in the ZrO 2–SiO 2 system

Sol–gel films and thin coatings are useful materials to be applied in a wide variety of optical devices. Particularly, sol–gel coatings behave as appropriate hosts for organic dyes that can be used as optical sensitive dopants. With the aim to check hydrolytic resistance and optical quality of sol–gel matrices to be used in further sensor applications, coatings in the ZrO 2–SiO 2 system have been prepared. Different starting precursors were used and several heat treatments were performed. Multilayer coatings were also obtained in the 50ZrO 2.50SiO 2 composition. Hydrolytic resistance tests at room temperature were carried out. Influence of thermal densification degree of coatings upon hydrolytic resistance was evaluated by determining the ultraviolet (UV) absorption edge. Microstructure of samples before and after resistance tests were observed by transmission and scanning electron microscopy. Results indicate that the effect of treatment temperature is the main variable affecting chemical durability of samples. The presence of organics and residual water also played an important role, together with the percentage of ZrO 2 and the use of organic–inorganic precursors. Conditions in which cracks appeared upon coatings were also discussed, as well as their influence on the results of further hydrolytic resistance tests.

Optical gradient materials produced via low-temperature isothermal frontal polymerization

Using a newly developed low-temperature frontal polymerization technique, poly(methyl methacrylate) (PMMA) matrices were prepared with nonuniform distributions of organic nonlinear optical dyes, with potential use as optical limiters. This technique affords lower temperature conditions than have been used before. A PMMA tube was filled with a dye, the initiator tert-butyl peroxide, and methyl methacrylate (MMA). Curing at 4°C resulted in a radial gradient of dye. An axial dye gradient was observed when MMA was overlaid and polymerization effected from a dye-doped PMMA seed using tricaprylmethyl ammonium persulfate as the initiator. In both cases, polymerization reactions were observed as a result of isothermal frontal polymerization with the subsequent formation of a nonlinear concentration distribution of the optical dye dopants. Low temperatures are desirable to eliminate thermal and photothermal degradation of temperature-sensitive dyes during the polymerization. The preparation of long polymer rods with organic dye gradients on the scale of several centimeters can also be realized with the use of low-temperature polymerization and the gradients controlled by the concentration of initiator. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 686–691, 2001

Infrared response and quantum efficiency of In-doped silicon (n) structure

In this paper the indium will be examined to be used as an electrical and optical dopant with the n-type silicon wafer to fabricate the indium-doped silicon (n) structure. The subgap response of the resulted structure is particularly strong and extends up to wavelengths of 1100 nm and above, while the response of the structure is very poor at the visible region. The structure has a maximum external and internal quantum efficiency at awavelength equal to 1100 nm.

Ion implantation for photorefractive devices and optical emitters

For the development of optical devices both defect engineering and dopant introduction are the most important current uses of ion implantation. Defect engineering is a well-established concept for changing the optical index. Especially in well-ordered crystalline materials, as the optical ferroelectrics, the nuclear recoils from ion implantation generate disorder, which lowers the polarizability and the optical index. Since MeV implantation of light ions provides the largest damage at the end of the ion range, numerous optical waveguides have been formed by the low index barrier in the depth. In addition, it could be demonstrated recently, that the implantation generated Frenkel defects within the oxides are electrically active. They can be used to improve the photorefractive (PR) properties significantly, as has been shown for single crystals of KNbO3.In the second part we will briefly mention the latest results of different groups on the luminescence of some rare earth ions, as Tb or Er, implanted into oxides or into silicon in the form of an erbium–oxygen complex. These ions from luminescent centers, which can be activated by the impact of electrons or the recombination of electron–hole pairs. The experiments are motivated by the search for optical electroluminescent emitters, being compatible with silicon-based microelectronics.

Enhanced electro-optic response of layered composite materials

We have constructed a multilayered composite material consisting of alternating layers of rf-sputtered barium titanate and spin-coated polycarbonate containing a third-order nonlinear optical organic dopant. The effective nonlinear susceptibility of the composite describing the quadratic electro-optic effect was measured to have the value χ(3)=(3.2+0.2i)×10−21±25% (m/V)2. The real part of this value is a factor of 3.2±50% times larger than that of the doped polycarbonate, which is the dominant electro-optic component of the composite. We have modeled the experiment by using both effective medium theory and by solving the wave equation for our multilayered system, and we find that these approaches give consistent predictions which are in good agreement to the experimental results.

Second harmonic generation of N-(4-nitrophenyl)-l-prolinol-doped alumina film prepared by a sol-gel process

A second harmonic generation (SHG) active non-linear optical alumina film has been prepared by aligning the non-linear optical dopant, N-(4-nitrophenyl)-l-prolinol, in the alumina matrix by a sol—gel process. The enhancement of SHG may be described by the formation of a pseudo-boehmite film in which the plate-shaped alumina sol particles are stacked in a card-pack structure.