Spectroscopic study of Cu²⁺ and Cu⁺ ions in high-transmission glass. Electronic structure and Cu²⁺/Cu⁺ concentrations

This work investigates the formation of photoluminescence centres in high-transmission glass (HTG) doped with Cu₂O and their capability to transform the solar spectrum by absorption/emission via Stokes-shifted PL into a more efficient spectrum for photovoltaic applications. Among the centres formed in HTG, both green photoluminescent Cu⁺ and the non-photoluminescent Cu²⁺ centres are created but their relative concentration depends on the thermal treatment and the presence of other co-dopants. The measurement of the absorption coefficient α(λ) nearby the HTG optical gap for Cu⁺ bands is accomplished by following the two-thickness method. This procedure allows us to obtain the actual absorption coefficient for the spectrum of each formed centre, from which we obtain the relative concentration of Cu⁺/Cu²⁺ as well as their absolute values. The analysis of the spectra provides information on the absorption cross sections, transition energies and bandwidths, the knowledge of which is essential to check the suitability of such centres for photovoltaic applications in solar cells.