Role of annealing temperatures on structure polymorphism, linear and nonlinear optical properties of nanostructure lead dioxide thin films

The powder of as synthesized lead dioxide (PbO2) has polycrystalline structure b-PbO2 phase of tetragonal
crystal system. It becomes nanocrystallites a-PbO2 phase with orthorhombic crystal system upon
thermal deposition to form thin films. Annealing temperatures increase nanocrystallites size from 28
to 46 nm. The optical properties of a-PbO2 phase were calculated from absolute values of transmittance
and reflectance at nearly normal incidence of light by spectrophotometer measurements. The refractive
and extinction indices were determined and showed a response to annealing temperatures. The absorption
coefficient of a-PbO2 films is >106 cm
1 in UV region of spectra. Analysis of the absorption coefficient
spectra near optical edge showed indirect allowed transition. Annealing temperature decreases the value
of indirect energy gap for a-PbO2 films. The dispersion parameters such as single oscillator energy, dispersion
energy, dielectric constant at high frequency and lattice dielectric constant were calculated and
its variations with annealing temperatures are reported. The nonlinear refractive index (n2), third-order
nonlinear susceptibility (v(3)) and nonlinear absorption coefficient (bc) were determined. It was found
that v(3), n2 and b increase with increasing photon energy and decrease with increasing annealing temperature.
The pristine film of a-PbO2 has higher values of nonlinear optical constants than for annealed
films; therefore it is suitable for applications in manufacturing nonlinear optical devices