Solar ultraviolet-B detectors using Eu²⁺ doped alkali halide crystals

The continuous depletion of the ozone layer causes an increase in the ultraviolet-B (UV-B) reaching the Earth's surface. In this paper the behaviour of the KCl:Eu²⁺ under solar UV irradiation has been investigated. Considering the thermoluminescence (TL) excitation spectra, the geometrical solar radiation parameters (solar zenith angle related to the light path) and the atmosphere characteristics (ozone content, Rayleigh scattering and aerosols' concentration), the solar UV irradiation flux registered by the dosimeter has been simulated throughout the day. This modelled hourly signal agrees with the measured TL signal at different hours. Moreover, these curves throughout the day are compared to the convoluted signal obtained from a gaussian curve centred at different UV-C wavelengths and the same solar spectrum. This comparison supports the idea that the KCl:Eu²⁺ crystal behaves under the sun as a narrow band gaussian detector centred at about 265 nm, but with the main registered solar UV-B signal at 285 nm. On the other hand, a comparison of the KCl:Eu²⁺ system with commercially available broad band UV-B biological sensors (biometers), shows that the europium doped crystals are more sensitive to minor changes of the solar UV-B flux and therefore, it is a good instrument for the study of small ozone layer depletions.