The optical properties of the pure polymer film and polymer films doped with Phenol Red dye at different concentrations were investigated. The films were prepared using the casting technique. Poly (methyl-methacrylate) (PMMA) polymer was doped with the Phenol Red dye dissolved in a mixture of chloroform and little quantity of methanol, used as suitable solvent for both the dye and the polymer. The spectral absorption measurements of these films were carried out at different dye concentrations using UV-Vis double-beam spectrophotometer in the wavelength range 300 - 800 nm. The optical parameters of the prepared Phenol Red dye doped polymer films, absorption coefficient ( α), extinction coefficient ( κ), refractive index ( n), optical and electrical conductivities ( σopt and σelect), and optical energy band gap ( Eg), were determined. The results showed that the Phenol Red dye doped polymer film is a good candidate for photonic applications such as, solar cells, optical sensors, and other photonic devices.
The interest in the optical properties of organic materials has grown due to the wide range of applications in photonic devices, such as sensors, light emitting diodes, solar cells, limiters, and optoelectronic devices [
Organic dyes provide promising materials for photonic devices due to their excellent optical properties [
In the present work, pure and Phenol Red dye doped polymer films were prepared by casting method. The optical properties of the prepared films were investigated and their useful optical parameters were determined. The effect of dye concentration on the values of these parameters was also studied.
The molecular formula of the Phenol Red dye is C19H14O5S, and its chemical structure is shown in
The Ultraviolet-Visible (UV-Vis) absorption spectra of prepared Phenol Red dye doped polymer films were characterized by using Cecil double-beam spectrophotometer (model CE-75000) with the wavelength range 190 - 1100 nm. An uncoated glass slide was used as a reference sample for the absorption measurement.
The spectral distributions of the absorbance (A), the transmittance (T), and the reflectance (R) of the Phenol Red dye doped polymer films at different concentrations were plotted as a function of the wavelength in Figures 2-4, respectively. In
where I0 is the incident intensity of light, I is the output intensity of light, and L is the thickness of the absorbing medium. Equation (1) can be written as follows:
where
The values of α of the Phenol Red dye doped polymer films were calculated using Equation (2). The variation of α with the photon energy (hν) at different concentrations is displayed in
Extinction coefficient (k) of material is related to the absorption coefficient (α) according the following relation [
where λ is the wavelength of the incident photon.
Using the values of the corresponding α and Equation (3), the values of k for the Phenol Red dye doped polymer films at different concentrations were calculated for different values of incident photon energy (hν). The variation of k of the Phenol Red dye doped polymer film with the photon energy (hν) is plotted in
The refractive index (n) of the Phenol red polymer film was calculated using the relation [
where the optical reflectance (R) is given by the relation [
The optical conductivity of the material is given by the following relation [
where c is the velocity of light.
The electrical conductivity (σelect) of the Phenol Red dye doped polymer film is related to its optical conductivity (σopt) according to the following relation [
We used, respectively, Equations (6) and (7) to calculate σopt and σelect of the Phenol Red dye doped polymer films. The variations of σopt and σelect with incident photon energy are shown in
(sec)−1, while the values of σelect are within the range (3 - 6) (Ω∙cm) −1, over the dye concentration range (0.05 - 0.40) mM. It is seen that the value of σelect is high at the low photon energies and decreases with increasing hν.
The optical energy band gap (Eg) of the film is related to its absorption coefficient (α) and the energy of the incident photon (hν) according to the following relation [
where h is the Planck’s constant, ν is the frequency of incident radiation, B and m are constants. The value of m is dependent on the type of transition between the valence band and the conduction band of the material. m takes the values: 2, 3, 1/2, or 3/2, for allowed direct, forbidden direct, allowed indirect, or forbidden indirect, transitions, respectively. In the present work, the analysis of UV-V is absorption spectra revealed that the dye doped polymer films, have allowed indirect transitions, therefore the value of m = 1/2 was used in Equation (8) for the Eg determination. The values of Eg of the pure and the Phenol Red dye doped polymer films, with the dye concentrations 0.05, 0.30, and 0.40 mM, were obtained from extrapolating the straight-line portions of the curves (αhν)1/2 versus hν to the hν-axis (where αhν = 0), as shown in
Optical energy band gap (Eg) (eV) | Sample |
---|---|
4.73 | PMMA |
4.71 | PR 0.05 mM |
1.63 | PR 0.30 mM |
1.61 | PR 0.40 mM |
of Eg for the dye doped polymer films were found to be in the range of (4.71 - 1.61) eV, when the dye concentration increased over the range (0.05 - 0.40) mM. The decrease in the value of Eg might be due to the formation of defects in the polymer matrix, which results in creation of localized sublevels in the optical band gap and consequently decreased the energy band gap.
The pure and Phenol Red dye doped polymer films were synthesized using the casting technique and their optical properties were investigated for different dye concentrations. The main optical parameters of the dye doped polymer films were determined for different dye concentrations. Results showed that the optical properties of the PMMA polymer film were appreciably modified in the presence of the organic Phenol Red dye. The optical energy band gap (Eg) values of the prepared polymer films show the decreasing trend with an increasing concentration of Phenol red dye. The obtained results from the investigation suggest that the prepared Phenol Red dye doped polymer films are useful for potential applications in solar cells, as well as in optoelectronic and photonic devices.
Imad Al-Deen Hussein A. Al-Saidi,Faisal Sadik, (2016) Synthesis and Investigation of Phenol Red Dye Doped Polymer Films. Advances in Materials Physics and Chemistry,06,120-128. doi: 10.4236/ampc.2016.65013