Strain modulated luminescence in (Ca,Sr)TiO3:Pr3+ perovskite thin films

Abstract

We report in-plane strain effect on the photoluminescence property of perovskite phosphor thin films. Epitaxial perovskite thin films of Ca0.6Sr0.4TiO3:Pr3+ phosphor were prepared on perovskite oxide substrates with different lattice constant a, LaAlO3 (LAO, a = 3.815 Å), (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7(LSAT, 3.868 Å), and SrTiO3 (STO, 3.905 Å) by a pulsed laser deposition method. From X-ray diffraction, the lattice constants of thin films on LAO, LSAT, and STO substrates were (a, c) = (3.815 Å, 3.956 Å), (3.871 Å, 3.880 Å), and (3.905 Å, 3.865 Å), respectively. Therefore it was confirmed that compressive-strained (∼4%), nearly strain-free, and tensile-strained (∼1%) films were obtained on the LAO, LSAT and STO substrates, respectively. Under N2 laser excitation at 337 nm which is above bandgap energy of thin films, the CSTO film on STO (tensile-strained) and on LSAT (strain-free) substrate showed intense red photoluminescence peaking at 612 nm due to Pr3+:1D2→3H4 transition and no photoluminescence lines from the 3PJ revels were observed at 300 K. On the other hand, the phosphor film on LAO (compressive-strained) showed blue and red luminescence which ascribed to the transitions from the Pr3+:3P0 level below 200 K. These results showed that initial state of photoluminescence can be tuned from the 1D2 level to the 3P0 level by biaxial strain not by composition in the Pr3+ doped perovskite phosphor films. The temperature dependence of photoluminescence was also explained by simplified four-level-model with carrier-trapping-center probably related to Ti center.