Optically stimulated luminescence of CaF2:Tm

Enhancement of 1.5 μm fluorescence signal from Er3+ due to Yb3+ in yttrium silicate powders pumped at 975 and 808 nm

The effect of the presence of ytterbium (Yb³⁺) on the near-infrared (NIR) emission profile of erbium (Er³⁺), more specifically the ⁴I_13/2 → ⁴I_15/2 radiative transition around 1.5 μm, in yttrium silicate crystalline ceramic powders prepared by combustion synthesis was investigated under different NIR laser excitation wavelengths (λ = 808 and 975 nm). Enhancement of fluorescence around 1.5 μm due to the presence of Yb³⁺ was observed, which has potential use in medicine (NIR-III biological window) and optical communications (C-band transmission window). Two different excitation channels involving energy transfer between Er³⁺ and Yb³⁺ were studied: one involving the sensitization of Er³⁺ by Yb³⁺ (for λ = 975 nm laser light excitation) and the other involving direct excitation of Er³⁺ with Yb³⁺ acting as an energy reservoir (for λ = 808 nm laser light excitation). The energy transfer mechanisms of both processes are discussed in the text.

OSL dosimetric properties and efficiency of Brazilian natural calcium fluoride pellets

Calcium fluoride (CaF₂), in both natural and synthetic forms, has been exhaustively studied and explored as thermoluminescent (TL) detector. However its sensitivity to ambient light points to the applicability of CaF₂ as OSL (Optically Stimulated Luminescence) detector, increasing the research about its luminescent properties. Although some properties to employ CaF₂ detectors with OSL technique have been already demonstrated, there is a lack of some essential information as the OSL response to different types and energy of ionizing radiation. In order to extend the use of Brazilian natural CaF₂ with OSL technique, we evaluated the efficiency and dosimetric properties of cold pressed CaF₂:NaCl pellets. The CaF₂ detectors presented good reproducibility and negligible fading of the signal over one month after irradiation. The dose response using OSL, TL and residual TL showed linear behavior for different radiation beams (protons, photons and alpha and beta particles), being equivalent to the results obtained with BeO and MTS (LiF) detectors through OSL and TL technique respectively. Moreover, differences were observed in OSL efficiency according the beam type and energy; CaF₂ detectors presented a higher OSL and TL sensitivities to protons, photons and beta particles than to alpha particles. The energy response to photons obtained using OSL and residual TL intensities present an over response at lower photon energy similar to TL energy response. In addition, differences in the OSL curve shapes were observed according to radiation type and energy, pointing to the possibility of applying this material in mixed radiation fields and to estimate average LET (Linear Energy Transfer).