Aliovalent ion doped n-type semiconductor nanocrystals (NC) have presently gained high interest in semiconductor research for their potential applications in plasmonics, transparent conducting oxide (TCO), and high speed optical device. For most of the cases the plasmonic absorbance band appears in the near infrared region (NIR) but it is rarely observed in visible wavelength for aliovalent ion doped semiconductor nanocrystals. In this article, we report the synthesis of Sn-doped ZnO monodispersed nanocrystals and their unique plasmonic absorbance property which is tunable from the visible to the NIR region (550 nm to >3000 nm) by varying the Sn dopant concentration and the degree of Cd-alloying. We have studied the surface enhanced Raman spectroscopy (SERS) of the 4-mercaptopyridine (4-MPy) molecule using Sn:ZnO NC thin film as SERS substrate and found a high enhancement factor value. A TCO thin film with a good figure of merit value has been prepared by Sn:Zn–Cd–O alloyed NCs by taking advantage of high electron density and high mobility of electrons of doped alloyed NCs. Application as SERS substrate and TCO are excellent features of Sn-doped Zn1–x Cd x O NCs.

We report a robust methodology for synthesizing monodisperse alloyed Bi 2 S 3−x Se x nanorods (NRs) to tune optical properties with the variation of Se concentration. The intercalation of Cu(I) into the presynthetic Bi 2 S 3−x Se x NRs converted to ternary Cu 3 BiS 3−x Se x NRs via cation exchange process. The transformation was monitored through the formation of core/shell Bi 2 S 3−x Se x / Cu 3 BiS 3−x Se x nanorod heterostructures. Shape anisotropy results in near-infrared bimodal localized surface plasmon resonance (LSPR) in Cu 3 BiS 3−x Se x nanorod over a broad range from 600 to 3500 nm with increase of Se:S ratio. The LSPR sensitivity, defined as the change in the LSPR peak wavelength per unit change in the refractive index (RI) of the medium, was estimated to be 250−350 nm/RI unit, much higher than other copper chalcogenides like Cu 2 S/Cu 2 Se. A fast photodetector was fabricated by Cu 3 BiS 3−x Se x NRs with high photocurrent gain value (∼125) with Se alloying. The intrinsic Cu vacancies and the effective mass of charge carriers play important roles to manipulate optical and electrical properties of Cu 3 BiS 3−x Se x NRs.

For increasing demand of electrochromic smart window, flat panel display synthesis of high quality aliovalent doped wide bandgap semiconductor nanocrystals are gaining interest. In our manuscript we synthesized pure and Nb 5 + doped anatase TiO 2 nanocrystals by colloidal process. On increasing doping percentage size of TiO 2 nanoparticle was found to be decreased. Although pure TiO 2 nanocrystals are terminated with thermodynamically stable {101} facets but Nb 5 + doped TiO 2 was found to be terminated with high energy {103} facet by lowering the surface energy. Successful doping in anatase TiO 2 has been characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR) analysis. Aliovalent dopant Nb 5 + generated free carriers in conduction band of TiO 2 . These free electrons results distinct plasmon absorption peak which appeared at wavelength of 1900 nm to 2700 nm. Plasmon peak found to be blue shifted with increase of dopant amount. Broad emission bands correspond to distinct transitions related to intermediate energy levels induced by oxygen vacancy. High colloidaly stable nanocrystals was deposited as crack free transparent conducting oxide thin film where we obtained very low sheet resistance with high optical transparency that leads to good figure of merit of thin film. Temperature driven metalinsulator transition for the lowest resistance film is explained by electron localization origination from random substitution of Nb into TiO 2 nanocrystals.

Solid solution of nickel ferrite (NiFe2O4) and barium titanate (BaTiO3), (100-x)BaTiO3–(x) NiFe2O4 has been prepared by solid state reaction. Compressive strain is developed in NiFe2O4 due to mutual structural interaction across the interface of NiFe2O4 and BaTiO3 phases. Quantitative analysis of X-ray diffraction and X-ray photo electron spectrum suggest mixed spinel structure of NiFe2O4. A systematic study of composition dependence of composite indicates BaTiO3 causes a random distribution of Fe and Ni cations among octahedral and tetrahedral sites during non-equilibrium growth of NiFe2O4. The degree of inversion decreases monotonically from 0.97 to 0.75 with increase of BaTiO3 content. Temperature dependence of magnetization has been analyzed by four sublattice model to describe complex magnetic exchange interactions in mixed spinel phase. Curie temperature and saturation magnetization decrease with increase of BaTiO3 concentration. Enhancement of strain and larger occupancy of Ni2+ at tetrahedral site increase coercivity up to 200 Oe. Magnetostructual coupling induced by BaTiO3 improves coercivity in NiFe2O4. An increase in the demagnetization and homogeneity in magnetization process in NiFe2O4 is observed due to the interaction with diamagnetic BaTiO3.

Cation exchange mediated synthesis of nanoheterostructures (NHSs), core–shell structure or segmented nanostructures are gaining high interest in nanoscience research as the process gives a wide window of opportunity to tune and enhance the photophysical properties of semiconductors. Presence of point defects or layered structure of the material accelerates cation exchange process, which is well established for copper chalcogenide system. Here, we are reporting facile synthesis of high-quality Fe7S8 hexagonal nanoplate by colloidal synthesis route and studied the effect of Cu­(I) ion addition by in situ and ex situ condition. The addition and consequent increase of Cu­(I) precursor concentration to presynthetic Fe7S8 nanocrystals (ex situ) leads to successive compositional and morphological transformations as follows: Fe7S8 (hexagonal nanoplate) → Fe7S8@Cu5FeS4 (multigrained heterostructure) → Cu1.97S/Cu5FeS4/Cu1.97S (nanodumbbell) → Cu1.97S/Cu5FeS4 (segmented nanohat) → Cu1.97S (nanodisk). Native Fe vacancies in layered crystalline structure of original Fe7S8 drive intercalation and cation exchange processes to stabilize a particular NHS. Different diffusion rates and channels of incoming Cu and outgoing Fe ions result in linear and bent nanodumbbells. The position of strong localized surface plasmon resonance (LSPR) band in NHSs is shifted from visible region to infrared region of the spectrum due to the variation of hole concentration originating from intrinsic Cu vacancy. The LSPR bands in NHS are further tuned by generating more holes through oxidation of Cu­(I) → Cu­(II) reaction in oxygen atmosphere. Shape anisotropy in NHS gives rise to multiple plasmon modes. Fe7S8 (hexagonal nanoplate) and Cu1.97S/Cu5FeS4/Cu1.97S (nanodumbbell) exhibit features of ferrimagnetism with transition temperature of above 300 and 320 K, respectively. In situ chemical synthesis using same Cu and Fe precursors as that of ex situ process yields CuFeS2 and Cu5FeS4 phases under Cu-deficit and Cu-rich environment. The LSPR resonance bands with high plasmonic sensitivity are also tuned by controlling the hole concentration.