Control of the luminescent properties of Eu2-xDyx(WO4)3 solid solutions for scintillator applications

Crystalline materials containing tungsten and europium ions are frequently used as scintillators because tungsten complexes show a high absorption cross section for high energy radiation and efficient energy transfer to europium ions, which relax radiatively in the visible spectral range according to the 5D0→7F2 transition. However, this intra-configurational transition is forbidden on spin and parity and, consequently, shows a slow decay rate (hundreds of microseconds to milliseconds). In order to use this kind of materials in high repetition rate processes, faster luminescence decays are required. A set of Eu2-xDyx(WO4)3 solid solutions has been synthesized. Rietveld refinement of X-ray diffraction patterns has been performed in order to determine the crystalline structure of the samples and particularly the distance between rare earth cations. The morphology and composition was characterized with scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. Optical absorption, emission spectra and decay rates have been systematically measured to analyze the luminescent properties of the materials. Cross-relaxation processes between Eu3+ and Dy3+ ions are responsible of the reduction of the 5D0 decay rate. The average lifetime of the Eu3+5D0 excited state can be decreased in the range of one order of magnitude. However, the 5D0→7F2 emission intensity decreases in the same range too. Nevertheless, the proposed strategy of Eu3+5D0 lifetime reduction can be of interest for those opto-electronic detection applications, which are not limited by sensitivity but by time resolution, such as it occurs in many cases for high energy-high repetition rate photon pulses.