A The main charge carrier in the ionic crystal is polaron or conduction?

[Alkrima]

TL;DR Summary

Suppose I have a perfect crystal(e.g.TiO2-Rutile, band gap=3ev), under UV light, there should photoconductivity, according to the condensed matter theory, some of these excited conduction band electrons would form small polarons, I am wondering how many percent of the free conduction band electrons would form polarons, and how many of them would stay as free electrons until recombination with holes?

Suppose I have a perfect crystal(e.g.TiO2-Rutile, band gap=3ev), under UV light, there should photoconductivity, according to the condensed matter theory, some of these excited conduction band electrons would form small polarons, I am wondering how many percent of the free conduction band electrons would form polarons, and how many of them would stay as free electrons until recombination with holes?

 

[Baluncore]

Welcome to PF.
The answer will depend on the intensity, and also the wavelength of the UV light.

 

[Useful nucleus]

Upon reaching equilibrium, quantum mechanical calculations show that in rutile-TiO2 the dominant form is small electron polarons. In anatase-TiO2, the dominant form is free-like electrons (or large polarons).
See for example:
https://pubs.rsc.org/en/content/articlelanding/2014/cp/c4cp03981e