Energy-transfer process in rare-earth-ion doped SrTiO3

Enhancement of emission intensity of rare-earth-ion doped SrTiO3 by Al addition has been investigated. In the case of Pr3+ and Tb3+, addition of 23-mol% Al intensifies emission by more than 200 times. In contrast, the addition of 20 mol% Al intensifies emission at most by three times in the case of other rare-earth ions. The temperature dependence of PL spectra. shows that the energy transfer from carriers to Pr3+ or Tb3+ ions is much more efficient than that to other rare-earth ions in SrTiO3. It can be speculated that the energy transfer in SrTiO3:Pr3+ or Tb3+ occurs from carriers to Pr3+ or Tb3+ ion via 4f-5d transitions, which are much higher in oscillator strength than 4f-4f transitions.