“…[4][5][6] The transfer of this effect to the upconversion phosphor sodium yttrium fluoride NaYF 4 :Er,Yb and the investigation of this material as a potential dosimetric material is, however, relatively new. 7,8 Although the precise nature of the radiation-induced effect in NaYF 4 :Yb 3+ ,Er 3+ remains to be clarified, the decrease in luminescence decay time is attributed to a higher probability for non-radiative decay of the 2 F 5/2 level in Yb 3+ , in analogy to BaYb 2 F 8 :Er. 5 Nevertheless, the decay time of the luminescence is independent of its intensity, and, in case the phosphor is used as a dose-sensitive component for dosimetry, the measurement signal, in general, is not dependent on the dosimetric layer thickness or the amount of dosimetry material.…”