A study of the impact of oxygen vacancies on the VUV efficiency of rare-earth doped YBO3 via Ca2+ co-doping

Vacuum ultraviolet excitation and reflectance spectroscopy were used to study doped yttrium borate phosphors with composition Y1-x-yBO3:REy, Cax up to x = 0.10 and up to y = 0.06 (Eu3+ or Tb3+). These data were used to estimate host-to-activator energy transfer efficiencies. The introduction of Ca2+ leads to the formation of oxygen vacancies, VOâ—â—, that act as energy traps. We find that the introduction of these defects lowers the transfer efficiency to both dopants, with Eu3+ being impacted more than Tb3+. The results are discussed in terms of the energies of dopant states relative to band states, and the difference in trapping mechanisms between the two rare earth ions.