Ram Kripal

Photoluminescence and photoconductivity of ZnS:Mn2+ nanoparticles synthesized via co-precipitation method

Mn(2+) doped ZnS nanoparticles are characterized using UV-vis, photoluminescence and photoconductivity studies. The size of Mn(2+) doped ZnS NPs is estimated to be 2-4nm by X-ray diffraction. UV-vis spectra show a blue shift in absorption edge as compared to bulk counterpart. Photoluminescence spectra indicate that orange luminescence varies with Mn(2+) concentration. The Mn(2+) doped ZnS nanoparticles are found to be photosensitive. The doping of Mn(2+) ions improves the photosensitivity of the ZnS nanoparticles system. The time-resolved rise and decay of photocurrent indicate anomalous behavior during steady state illumination.

Photoconductivity and photoluminescence of ZnO nanoparticles synthesized via co-precipitation method

Photoconductivity and photoluminescence studies of ZnO nanoparticles (NPs) synthesized by co-precipitation method capped with thioglycerol are carried out. The effect of annealing at 300°C is also studied. The transmission electron micrograph (TEM) and X-ray diffraction (XRD) pattern confirm the hexagonal wurtzite structure of ZnO nanoparticles. The UV-vis absorption spectrum of ZnO NPs shows blue shift of absorption peak as compared to bulk ZnO. The photoluminescence (PL) spectra of as-synthesized ZnO NPs show band edge emission as well as blue-green emission. After annealing band edge emission is quenched. Photocurrent is found to vary super linearly at high voltage for both as-synthesized as well as annealed ZnO NPs. Time resolved rise and decay photocurrent spectra are found to exhibit anomalous photoconductivity for as-synthesized as well as annealed ZnO NPs wherein the photocurrent decreases even during steady illumination.

Studies of the ground state wave function and the g-anisotropy of the Cu2+ ion in different lattices

Abstract The ground state wave function of the Cu 2+ ion in different lattices is determined from the spin-hamiltonian constants obtained from ESR studies. It is found that the ground state may be predominantly 1 x 2 - y 2 ) in some cases, and 13= 2 - r 2 ) otherwise. The g -factor anisotropy is also calculated and compared with the experimental value. However, the approach is of approximate nature.

EPR and photoluminescence properties of Mn2+ doped CdS nanoparticles synthesized via co-precipitation method

The structural properties of Mn doped CdS (Mn:CdS) nanoparticles (NPs) are studied using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Ultraviolet-visible (UV-vis), Photoluminescence (PL), Raman and Electron paramagnetic resonance (EPR) spectroscopy. XRD analysis shows the nanostructure with 2-4 nm of average crystallite size. The planes (110), (103) and (112) in XRD pattern distinguish the wurtzite structure of the Mn:CdS NPs. The intensity of the plane (102) increases as the doping concentration of Mn(2+) increases. UV-vis absorption spectra show blue shift as compared to bulk CdS. The optical band gap energy of Mn(2+) (0, 0.35, 0.70 and 1.35 at.%) doped CdS NPs corresponding to absorption edge are found to be 5.29, 5.28, 5.25 and 5.21 eV, respectively. The intensity of luminescence is changing with the concentration of Mn(2+) doped in CdS NPs. Raman spectra show blue shift in fundamental optical phonon mode (1LO) as well as second optical phonon mode (2LO) as compared to bulk CdS. The intensity ratio of the 2LO to 1LO modes slightly decreases as Mn(2+) concentration increases. EPR shows the existence of Mn(2+) with different local structures in CdS nanoparticles. The values of spectroscopic splitting factor (g) and hyperfine interaction constant (A) decrease as Mn(2+) concentration increases in CdS NPs.

EPR, optical absorption and superposition model study of Fe3+ doped strontium nitrate single crystals

Electron paramagnetic resonance (EPR) study of Fe³(+) ions doped strontium nitrate (SN) single crystals is performed at liquid nitrogen temperature and at X band frequency. The spin Hamiltonian (SH) parameters are determined from the resonance lines observed at different angular rotations. The crystal field parameters (CFPs) are evaluated using superposition model of Newman. The Zeeman g-factor and zero-field splitting parameters (ZFSPs) of Fe³(+) ion in SN (truncated SH considered) are: g=1.9989 ± 0.002 and ∣D∣=(338 ± 5) × 10⁻⁴ cm⁻¹, ∣E∣=(10 ± 5)× 10⁻⁴ cm⁻¹, a=(458 ± 5)× 10⁻⁴ cm⁻¹, respectively. The Fe³(+) ion enters the lattice substitutionally replacing the Sr²(+) sites of cubic symmetry. The local site symmetry of Fe³(+) ion in the crystal is orthorhombic (lower than that of the host). The optical absorption study of the crystal is also done at room temperature in the wavelength range 195-925 nm. The energy values of different orbital levels are determined. The observed bands are assigned as transitions from the (6)A₁(g)(S) ground state to various excited states of Fe³(+) ion in a cubic crystal field approximation. The observed band positions are fitted with four parameters, the Racah interelectronic repulsion parameters (B and C), the cubic crystal field splitting parameter (Dq) and the Trees correction (α) yielding: B=934, C=2059, Dq=1450, and α=90 (in cm⁻¹). On the basis of EPR and optical data, the nature of metal-ligand bonding in this crystal is discussed. The ZFSPs are also determined theoretically using microscopic SH theory based on perturbation theory and CFPs, B(kq) obtained from superposition model. The values of ZFSPs thus obtained are ∣D∣=(340 ± 5) × 10⁻⁴ cm⁻¹ and ∣E∣=(15 ± 5) × 10⁻⁴ cm⁻¹.

ESR of Copper Doped Calcium Propionate

Electron spin resonance (ESR) of Cu 2+ doped calcium propionate has been studied at room temperature. Spin Hamiltonian parameters are calculated from the ESR absorption spectra which are g x =2.1285±0.002, g y =2.1868±0.002, g z =2.2205±0.002, A x =(121±2)×10 -4 cm -1 , A y =(140±2)×10 -4 cm -1 and A z =(142±2)×10 -4 cm -1 . It is found that Cu 2+ enters the lattice interstitially. The ESR results indicate that the copper complex possesses rhombic symmetry. The ground state wave function of Cu 2+ ion in this lattice is also determined from the spin-Hamiltonian constants obtained from ESR results. It is found that the ground state is predominantly | x 2 - y 2 >.

EPR and optical study of Mn2+ doped ammonium tartrate single crystals.

EPR study of Mn2+ doped ammonium tartrate single crystals is carried out at room temperature. The spin Hamiltonian parameters are: gx=1.9225+/-0.0002, gy=1.9554+/-0.0002, gz=2.1258+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(191+/-2) x 10(-4) cm(-1), E=(61+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site I and gx=1.9235+/-0.0002, gy=1.9574+/-0.0002, gz=2.0664+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(180+/-2) x 10(-4) cm(-1), E=(57+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site II, respectively. The observed optical bands are fitted with inter-electronic repulsion parameters (B and C), crystal field parameter (Dq) and Trees correction (alpha) and the values found are B=752, C=2438, Dq=765 and alpha=76 cm(-1). The data obtained are further used to discuss the surrounding crystal field and the nature of metal-ligand bonding in the crystal.

EPR and optical absorption studies on VO2+ ions in L-asparagine monohydrate single crystals.

X-Band electron paramagnetic resonance (EPR) studies of VO(2+) ions in l-asparagine monohydrate single crystals have been done at room temperature. Detailed EPR analysis indicates the presence of two magnetically inequivalent VO(2+) sites. Both the vanadyl complexes are found to take up interstitial position. The angular variation of the EPR spectra in three planes ab, bc and ca are used to determine principal g and A tensors. For the two sites the spin Hamiltonian parameters are, site I: g(x)=1.9633, g(y)=2.0274, g(z)=1.9797, A(x)=88, A(y)=61, A(z)=161x10(-4)cm(-1); site II: g(x)=1.9627, g(y)=1.9880, g(z)=1.9425, A(x)=90, A(y)=66, A(z)=167x10(-4)cm(-1). The optical absorption study is also carried out at room temperature and absorption bands are assigned to various transitions. The theoretical band positions are obtained using energy expressions and a good agreement is found with the experimental values. By correlating EPR and optical data different molecular orbital coefficients are evaluated and the nature of bonding in the crystal is discussed.

ESR and optical study of Mn2+ doped ammonium selenate single crystals

ESR and optical absorption studies of manganese doped ammonium selenate single crystals are performed at X-band and room temperature to ascertain the site symmetry and location of impurity ions in the lattice. Manganese ions are expected to enter the lattice interstitially. Various spin Hamiltonian parameters are determined. Optical absorption study is also done and associated distortion in the crystal lattice is estimated.

EPR and optical studies of Cu2+ ions doped in magnesium potassium phosphate hexahydrate single crystals

An electron paramagnetic resonance (EPR) study of Cu2+-doped magnesium potassium phosphate is performed at liquid nitrogen temperature (LNT; 77 K). Two magnetically non-equivalent sites for Cu2+ are observed. The spin Hamiltonian parameters are determined with the fitting of spectra to a rhombic symmetry crystalline field. The ground state wavefunction is also determined. The g-anisotropy is evaluated and compared with the experimental value. With the help of an optical study, the nature of the bonding in the complex is discussed.