Judd-Ofelt and quantum cutting analysis of Eu3+ or Pr3+ doped β-NaGdF4 nanorods obtained by rapid coprecipitation method

Pure hexagonal beta-NaGdF4 and Eu3+ or Pr3+-doped beta-NaGdF4 nanocrystals in shape of nanorods of similar to 140 nm of length have been synthesized using a simple and rapid coprecipitation method. XRD analysis evidenced pure single phases exhibiting characteristic luminescence of Eu3+ or Pr3+ ions when excited under UV or blue radiations. Samples gave rise to intense orange-red emission and quite white emission in the case of respectively Eu(3+)or Pr(3+)doped samples. Optical properties are discussed in the frame of Judd-Ofelt theory and considering that an energy transfer occurs between active ions. Notably it was found that the quantum-cutting by a two-step energy transfer from Gd3+ to Eu3+ can improve the red emission of Eu3+ ions under near-VUV excitation. Such quantum-cutting mechanism has been also considered in the case of Pr3+ doped beta-NaGdF4. However, the efficiency of both processes in comparison with literature suggest that only one part of the energy in the excited states within Gd3+ can be transferred to Eu3+ for its red emission. In the case of Pr3+ ions, the energy is more probably released through the self-trapped exciton emission certainly due to the lack of resonant VUV excitation.