Codoping Eu3+ with Sc3+ and La3+ in CaSnO3 for possible site selective doping: Is size selection in site selective doping really effective?

Abstract

Local site of dopant in host lattice with multiple cationic sites is very important from light emission perspective in dictating its various photophysical features. The same is very important particularly in perovskites which is considered a very important invention for optoelectronic applications. Here in this work we have investigated the local site of dopant and time resolved photoluminescence in CaSnO3:Eu red emitting phosphor on co-doping La3+ and Sc3+ based on their size proximity to A and B-site respectively. EXAFS spectroscopy suggested increase in coordination number of Eu3+ from 6 to 8 and formation of Sn and Ca vacancies as charge compensating defects (CCDs) in La3+ and Sc3+ co-doped samples respectively. Co-doping with either La3+or Sc3+ is directing more fraction of Eu3+ to asymmetric 8-coordinated Ca2+ site compared to relatively symmetric 6-coordinated Sn4+ site. Sc3+ codoping direct more Eu3+ to Ca2+ site but with less distortions in the lattice owing to smaller size of Eu3+ than Ca2+ and higher size of Sc3+ than Sn4+. In case of La3+ co-doping, directing Eu3+ to Sn4+ site is not so effective owing to larger size of Eu3+ than Sn4+ as well as La3+ than Ca2+ and both cause significant distortions in the lattice. PL intensity also improved in the co-doped samples with Sc3+ co-doping emerging victorious over La3+ due to better charge compensation encountered in the former. Excitation dependent PL suggested Eu3+ at Ca2+ sites is preferentially excited under 250 nm and Eu3+ at Sn4+ symmetric site is preferentially excited under 300 nm.