Tulika Srivastava

Opto-electronic properties of Zn(1-x)VxO: Green emission enhancement due to V4+ state

Vanadium incorporation in ZnO modifies the lattice structure. The valence state of V plays an important role, controlling the oxygen content and thereby dimensions of the lattice. Both V4+ and V5+ are more electropositive than Zn2+ and reduce oxygen vacancies, resulting in lattice expansion. However, the sizes of both V4+ and V5+ are smaller than Zn2+, thereby resulting in the lattice contraction. The internal competition of increasing oxygen content and reducing effective crystal radius decides the lattice expansion and contraction. This affects the lattice strain and changes electronic levels, which modify absorption and emission processes in between the valence and conduction bands. A strong green emission band not due to oxygen vacancy but due to defects contributed by vanadium is also dependent on the oxidation state of vanadium. Bandgap also increases with the increase in the V4+ content.

Effect of ionic size compensation by Ag+ incorporation in homogeneous Fe-substituted ZnO: studies on structural, mechanical, optical, and magnetic properties

Substituting an ion of different size from that of the host element introduces lattice strain and defects. However, this mismatch may be significantly reduced by substituting an additional ion with a compensating size relative to the dopant. Such a double substitution might offer better solubility irrespective of the local distortions as well as the formation of defects in the valence states. Fe-substituted ZnO has been widely reported with conflicting results primarily arising from lack of chemical and structural homogeneity originating from preparation techniques, compositional fluctuations, and equivocal comprehension of actual solubility limits of the dopants. In this study, Ag ion has been incorporated in Fe-substituted ZnO to compensate the ionic size of Zn1−x[Fe0.8Ag0.2]xO (0 ≤ x ≤ 0.03125) by determining the solubility limit of the homogeneous material and their corresponding structural, mechanical, optical and magnetic properties have been investigated thoroughly. Co-substitution rearranges the lattice and leads to better crystal structures with tunable properties related to the amount of substitution.

Vanadium substitution: A simple and economic way to improve UV sensing in ZnO

The UV sensing in pure ZnO is due to oxygen adsorption/desorption process from the ZnO surface. Vanadium doping improves the UV sensitivity of ZnO. The enhancement in UV sensitivity in vanadium-substituted ZnO is attributed to trapping and de-trapping of electrons at V4+ and V5+-related defect states. The V4+ state has an extra electron than the V5+ state. A V4+ to V5+ transformation happens with excitation of this electron to the conduction band, while a reverse trapping process liberates a visible light. An analytic study of response phenomenon reveals this trapping and de-trapping process.

Influence of Si incorporation on mechanical properties of ZnO particles

This study demonstrated the effect of Si doping on structural and mechanical behaviour of ZnO nano-particles synthesized through sol–gel method. Characteristic investigations have been carried out by X-ray diffraction, Field emission scanning electron microscope and micro-hardness tester. The results confirmed the formation of nano-particles in polycrystalline single phase with hexagonal wurtzite structure. The indentation size Effect was observed in micro-hardness and decreased with Si doping.

Structure, electronic and photoluminescence study of Si doped ZnO nano-particles

A detailed structural and electronicstudy of sol-gel synthesized and 1100°C calcined Zn1-xSixO (0 ≤ x ≤ 0.06) nano-particles were carried out using XRD, FESEM, UV- vis/PL spectroscopy studies. XRD reveals wurzite structure at (0 ≤ x ≤ 0.03) after which some extra phase is seen which is also supported by FESEM images.UVs spectroscopy revealed that band gap increases and urbach energy decreases with substitution. Due to doping of Si4+, oxygen deficiency is decreased which improve structural properties in spite of introduction of strains due to lattice contraction.Photoluminescence studiesrevealed that the reduction in defects state in the sample with Si4+ substitution.