TiO is used as a sunscreen, it has high absorption and emittance rates and a high radiation potential. SiO2 is used for fiber optic cables and probably deflects and transmits photons a lot more, and it is very chemically inert, that's why the desert is made of quartz, it's all that is left after the rest has been weathered, it's orbitals are very stable and difficult to change. That's why silicon life forms probably don't exist, especially in a water world, they can't really bond with H and they absorb oxygen very tenaciously.
When a molecule absorbs a wavelength of light, an electron is excited from a full orbital into an empty anti-bonding orbital. Each jump takes energy from the light, and a big jump obviously needs more energy than a small one. Each wavelength of light has a particular energy associated with it. If that particular amount of energy is just right for making one of these energy jumps, then that wavelength will be absorbed - its energy will have been used in promoting an electron.