D. H. Kim, C. H. Jeon and Y. S. Lee ∗ Department of Physics, Soongsil University, Seoul , South korea J. K. Han, Y. C. Choi and S. D. Bu Department of Physics, Chonbuk National University, Jeonju, , South Korea Journal of the Korean Physical Society, (2013) 1 Photoluminescence of Ultra-thin-walled Pb(Zr,Ti)O 3 Nanotubes Synthesized in the Porous Alumina Membrane Template-directed Method

Introduction 2  Multi-functional complex metal oxides  High-T c superconductivity  Colossal magnetoresistance  Ferroelectricity  Metal-insulator transitions  Nanotubes, new phenomena, which are unexpected in bulk, emerge due to the finite size effects and the large surface-to-volume ratio.  Ferroelectric nanotubes are of great interest because of their peculiar physical properties on a nanoscale and their wide range of potential applications such as piezoelectric actuators, force and acceleration sensors, ultrasonic transducers, photonic crystals, and nonvolatile memory devices.  Photoluminescence (PL) spectroscopy is known to be a powerful tool for investigating defects and structural disorder in oxides.

3 (a) FESEM image of a 60-nm-diameter PAM (b) FESEM image of the PAM after spin-coating with a PZT sol-gel solution. Note that the PZT-NTs are densely packed inside the PAM pores. (c) FESEM images of PZT-NT/PAM after partial etching on the top. The scale bars in the photos are 100 nm. Experimental  The PZT-NTs are synthesized by filling sol-gel precursor solutions into the nanopores of porous alumina membranes (PAMs) via spin- coating  Annealed at at 650 ◦ C, for crystallization of PZT.  The diameters of the nanopores in the PAMs vary from 60 to 420 nm.  Removed Top PAMs.  The PL spectra of the top-etched PZT-NT/PAM were measured using photo-excitation with a He-Cd laser (λ =325 nm)

4 Results & discussion Fig. 2. (Color online) Room-temperature PL spectra of PZT-NT/PAM with different NT diameters: (a) 60 nm, (b) 90 nm, (c) 280 nm, and (d) 420 nm. The PL spectra are fitted with three Gaussian modes: Peak 1 (blue lines), Peak 2 (green lines) Peak 3 (red lines). The arrows mark the center position of Peak 3. The thick line in (a) represents the emission spectrum of the 60-nm PAM. Inset of (b): Center position of Peak 3 (ωpeak) vs. nanotube diameter (φ). Inset of (c): binding energy (Eb) vs. nanotube diameter (φ).

5 Results & discussion Fig. 3. (Color online) Temperature-dependent PL spectra of the PZT-NTs/PAM with a diameter of 60 nm. Peak 1, Peak 2, and Peak 3 are represented by the violet, the blue, and the orange lines, respectively. The range of the y- axis in (a) is 5 times wider than that in (b).

6 Results & discussion Fig. 2. (Color online) Room-temperature PL spectra of PZT-NT/PAM with different NT diameters: (a) 60 nm, (b) 90 nm, (c) 280 nm, and (d) 420 nm. The PL spectra are fitted with three Gaussian modes: Peak 1 (blue lines), Peak 2 (green lines) Peak 3 (red lines). The arrows mark the center position of Peak 3. The thick line in (a) represents the emission spectrum of the 60-nm PAM. Inset of (b): Center position of Peak 3 (ωpeak) vs. nanotube diameter (φ). Inset of (c): binding energy (Eb) vs. nanotube diameter (φ).

7 Results & discussion Fig. 3. (Color online) Temperature-dependent PL spectra of the PZT-NTs/PAM with a diameter of 60 nm. Peak 1, Peak 2, and Peak 3 are represented by the violet, the blue, and the orange lines, respectively. The range of the y- axis in (a) is 5 times wider than that in (b).

8 Results & discussion Fig. 4. Temperature dependences of the peak position and intensity of (a) Peak 1, (b) Peak 2, and (c) Peak 3 for PZTNTs/PAM with a diameter of 60 nm Peak 3 for PZTNTs/PAM with a diameters of (d) 90, (e) 280, and (f) 420 nm.  C is a fitting parameter,  I 0 is the integrated PL intensity at zero temperature, which is approximately the same as that of the 10 K data,  E b is the binding energy between the donor and the free exciton E b to be 26.7, 27.4, 30.3, and 37.3 meVfor PZT-NTs with diameters of 60, 90, 280, and 420 nm, respectively.

9  We investigated the emission property of ultra-thinwalled PZT-NTs with various diameters synthesized by using PAM templates.  The intensity of the emission spectra appears to increase with increasing??(decreasing) diameter of the NTs, and the peak position shifted to lower energy.  The emission intensity is dramatically enhanced With decreasing temperature, and the peak position is shifted to lower energy. Conclusions