Figure 3
PL spectra of microtubes with different coating layers after different treatments. (a, b) PL spectra from the tubular microcavity after different treatments: (a) stored at 30 Pa and (b) heated at 150°C. (c, d) PL spectra from different tubular microcavities (reference samples) after heat treatment at 150°C: (c) microtube coated with 30-nm Al2O3 and (d) microtube coated with 30-nm TiO2.