Does Rayleigh scattering occur on the mesoporous TiO2? If it is true, near the tio2 which is unoccupied by sensitizer, the average density of blue light quanta must be more than the red light one, is not it?
Also, we got absorption spectra of the TiO2 layer on the glass, and we used air as a blank. In this spectrum, optical density of such object is equal or more than 4 until 400nm. Is it due to absorption or it can be caused by scattering? In this case, TiO2 was unsensitized.
We use TiO2 paste from solaronix.
Rayleigh scattering is only for small particles typically r < lambda/10 where lambda is the wavelength of incident light. Most TiO2's have sizes in the optimum range for scattering in the 300 nm region (into the Mie region) where Qext approaches 5 (use Phlip Laven;s excellent MiePlot program to show this). Blue light has higher energy than red light and Is thus more easily scattered (1/lambda4 dependence in the Rayleigh region). Plus there's an absorption band for TiO2 (depending on the form - rutile or anatase) below 420 nm or so -that's why it's used as a UV sunblock. For more diversion see:
August 11th 2011 Optical properties of the three forms of titanium dioxide
http://tinyurl.com/pbgf9hj
So both scattering and absorption can be factors.
There is certainly Rayleigh scattering involved, if you have such a high-index material with mesomores. However, it does not necessarily mean that you have a disproportionally high intensity of blue light - to really discuss this, you have to consider the this intensity distribution changes in the depth of your coating. The penetration depth of blue light should be substantially smaller than that of red light, so that starting from a certain depth, you'll have MORE RED than blue. If your optical density is above 4 over the whole spectral range, this means, first of all, that your coating is too think to perform any reliable measurement at all. To stay in the linear range of most UV-Vis spectrometers, the density should not exceed 2. If you really want to make sure what is scattering and what gets absorbed, you measurement of (diffuse) transmittance must be augmented by measuring diffuse reflectance.
Glass has a strong absorption up to ~350nm - which is why you don't get a suntan indoors!!! A significant contribution to your absorption spectrum will come from this! If you want to avoid this, you should use quartz or similar substrate which is transparent in this region!
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