The structure and photoluminescence of a ZnO phosphor synthesized by the sol gel method under praseodymium doping.

This work outlines some interesting results regarding the effects of Pr3+ substitution on the structural and optical properties of (x = 0 and 0.02) samples. Our samples were synthesized using the Pechini sol-gel method. The structural study using Rietveld refinement of XRD patterns showed a hexagonal structure with the P63mc space group for all the samples and also the existence of a secondary phase attributed to the praseodymium oxide (Pr6O11) for 2% wt Pr-doped ZnO. The refinement results revealed that both the lattice parameter and the unit cell volume increase with the increase of Pr content. X-ray peak broadening analysis was used to evaluate the crystallite size and lattice strain by the Williamson-Hall (W-H) method and size-strain plot method (SSPM). The physical parameters such as strain, stress and energy density values were also calculated using the W-H method with different models, namely uniform deformation model (UDM), uniform stress deformation model (USDM) and uniform deformation energy model (UDEDM). The obtained results showed that the mean particle size of the ZnO and Pr0.01Zn0.97O estimated from W-H analysis and the SSPM method are highly intercorrelated. Shifting of the absorption edge to lower wavelength and blue shift of the band gap are observed in the UV-visible spectra of Pr-doped ZnO samples. Particular emphasis was put on the PL measurements of such composites. A noticeable decrease of the maximum intensity of PL response was found after adding Pr3+ to ZnO. This finding is discussed in terms of the photo excited limitation of electron-hole pairs in such nanocomposites.

Influence of defect on the electrical and optical properties of A-site non-stoichiometry Ca0.67La0.22□0.11Ti(1-x)Cr x O3-δ perovskite.

An investigation of the dielectric dispersion, electrical properties, scaling behavior and optical defects of Ca0.67La0.22□0.11Ti(1-x)Cr x O3-δ (CLT(1-x)Cr x ) with x = 0 and x = 0.1 compositions is presented. The square in the formula is attributed to a vacancy in A-site. Relaxation phenomena were studied with dielectric and modulus formalism, while, the conductivity mechanism was investigated using electrical conductivity. A high permittivity of around 104, low dielectric loss and low electrical conductivity of around 10-3 S cm-1 for Ca0.67La0.22TiO3 (CLT) was observed. These values make this composition interesting for microelectric applications. A comparison between the Z'' and M'' indicated that the short-range carrier motion dominates at low temperature and becomes less localized at high temperature. The optical defects of CLT and Ca0.67La0.22Ti0.9Cr0.1O3 (CLT0.9Cr0.1) were studied by electron paramagnetic resonance (EPR) spectroscopy. The results suggest the formation of a [TiO6]9- center, a (Ti3+-V O) center, and dipole defect for CLT compound and Cr3+-V O center defect for CLT0.9Cr0.1 compound. These defects are the source of the in-gap electron traps, which improve the optical properties of CLT(1-x)Cr x and hence make it an interesting optical material for different applications.