Lanthanide doped oxides nano materials have novel optical, physical and structural properties. Cubic
Ho<sup>3+</sup>-Yb<sup>3+</sup>-Tm<sup>3+</sup> co-doped Gd<sub>2</sub>O<sub>3</sub> nanotubes are synthetize by a simple wet-chemical route at low temperature and
ambient pressure followed by subsequent annealing heat treatment in muffle furnace. Nanotubes are formed by adjusting
the pH value of reacting solution. The introduction of Yb<sup>3+</sup> leads to strong visible upconversion luminescence and
change the intensity ratio of the green, blue and red luminescence. In trichromatic laser display, research of how to
enhance blue light is in the bottleneck period. In the experiment, the blue emission has been successfully improved. In
certain doping ratio, distinct enhancement of blue emission and obvious degradation of green light have been observed,
which is discussed in detail. X-Ray powder diffraction (XRD), scanning electron microscope (SEM) and upconversion
(UC) emission spectra are used to characterize the sample. Strong and adjusted upconversion luminescence determine
that the nano material is a potential candidate for applications of biological probe, color displays, lighting and photonics.
The optical nonlinearities of bulk GaN single crystal are investigated by conducting Z-scan experimental measurements, using nanosecond pulses at 532nm. The material’s nonlinear absorptive and refractive optical nonlinearities are determined by measuring the normalized transmittance with and without an aperture in the far field. After simulating the experimental curves, the two-photon absorption (TPA) coefficient, especially the refractive-index change induced by two-photon-excited free carrier, are obtained. The experimental results show that GaN has reverse saturable absorption and self-defocusing effect at 532 nm, indicating this material is a good candidate for future photonics applications. The theoretical simulation fit well with experimental results.