J.L. Rao

Thermoluminescence and EPR studies of nanocrystalline Nd2O3:Ni2+ phosphor

Nanocrystalline Nd(2)O(3):Ni(2+) (2 mol%) phosphor has been prepared by a low temperature (∼400°C) solution combustion method, in a very short time (<5 min). Powder X-ray diffraction results confirm the single hexagonal phase of nanopowders. Scanning electron micrographs show that nanophosphor has porous nature and the particles are agglomerated. Transmission electron microscopy confirms the nanosize (20-25 nm) of the crystallites. The electron paramagnetic resonance (EPR) spectrum exhibits a symmetric absorption at g≈2.77 which suggests that the site symmetry around Ni(2+) ions is predominantly octahedral. The number of spins participating in resonance (N) and the paramagnetic susceptibility (χ) has been evaluated. Raman study show major peaks, which are assigned to F(g) and combination of A(g)+E(g) modes. Thermoluminescence (TL) studies reveal well resolved glow peaks at 169°C along with shoulder peak at around 236°C. The activation energy (E in eV), order of kinetics (b) and frequency factor (s) were estimated using glow peak shape method. It is observed that the glow peak intensity at 169°C increases linearly with γ-dose which suggest that Nd(2)O(3):Ni(2+) is suitable for radiation dosimetry applications.

Electron paramagnetic resonance and photoluminescence investigation on ultraviolet-emitting gadolinium-ion-doped CaAl12O19 phosphors

The gadolinium doped CaAl12O19 phosphor has been prepared by a low temperature solution combustion method in a short time and characterized using powder X-ray diffraction, energy dispersive analysis of X-ray mapping, electron paramagnetic resonance (EPR) and photoluminescence spectroscopic techniques. EPR and optical analysis of the sample confirm the presence of Gd(3+) in the CaAl12O19 matrix.

Combustion synthesized Fe doped CeO2 powder-characterization, optical absorption and EPR spectroscopy

Fe doped CeO2 powder was prepared using solution combustion method. Powder X-ray diffraction and scanning electron microscopy methods are used to characterize the combustion derived powder. The optical absorption spectrum exhibits three bands due to Fe3+ and Fe2+ ions. Electron paramagnetic resonance (EPR) spectrum of this sample exhibits number of resonance signals due to Fe3+ ions. The number of spins (N) participating in resonance and its paramagnetic susceptibility (χ) has been evaluated. From EPR and optical studies it is observed that iron ions are present in trivalent state.

Dazzling green emission from graphene oxide nanosheet-embedded co-doped Ce3+ and Tb3+:PVA polymer nanocomposites for photonic applications

Novel dazzling green emission has been obtained from graphene oxide nanosheet-embedded Ce3+ and Tb3+:PVA polymer nanocomposites under UV excitation. We have successfully synthesized Tb3+:PVA, Ce3+ + Tb3+:PVA and Ce3+ + Tb3+ + graphene oxide nanosheet (GO NS):PVA polymer films by the solution casting method. For these polymer films, their XRD and FTIR spectral profiles have been analyzed for structure details and ion–polymer interaction mechanism. Tb3+ doped at different concentrations in the PVA polymer films displayed a green emission at 546 nm (5D4 → 7F5) and under 370 nm (7F6 → 5L10) excitation. Upon co-doping with Ce3+ to the Tb3+:PVA polymer film, it exhibits enriched green emission compared to the single Tb3+:PVA under the same excitation due to energy transfer from Ce3+ to Tb3+. Surprisingly a common excitation band has been found at 370 nm for Tb3+, Ce3+ and the GO NS. After good dispersion of the GO NS in the co-doped Ce3+ + Tb3+:PVA polymer films, the photoluminescence properties are remarkably enhanced and a prominent green emission is observed at 370 nm. The green emission of Tb3+ is significantly enhanced though an efficient energy transfer process from Ce3+ to Tb3+ and the GO NS to Tb3+. A possible energy transfer mechanism is clearly demonstrated by several fluorescence methods and lifetime decay dynamics. From these results, these GO NS-embedded Ce3+ + Tb3+:PVA polymer films could be suggested as promising candidates for green luminescent materials for photonic devices.

Investigations of the optical and EPR properties of LiGa{sub 5}O{sub 8}:Cr{sup 3+} phosphor

Highlights: • Cr{sup 3+} doped LiGa{sub 5}O{sub 8} phosphor was synthesized by solution combustion synthesis. • Morphological studies show the non-uniform distribution of particles. • Photoluminescence spectra of Cr{sup 3+} doped LiGa{sub 5}O{sub 8} showed the characteristic Cr{sup 3+} peaks. • EPR spectrum showed Cr{sup 3+} ions in tetragonally distorted octahedral symmetry. - Abstract: Red emitting LiGa{sub 5}O{sub 8} doped with Cr{sup 3+} ions has been prepared by a low temperature solution combustion route. The as-prepared phosphor was studied using X-ray diffraction and scanning electron microscopic techniques. The optical spectrum exhibits two broad bands characteristic of Cr{sup 3+} ions in an octahedral symmetry. Upon excitation at 590 nm, the material displays narrow red emission line centered at 715 nm due to the {sup 2}E{sub g} → {sup 4}A{sub 2g} transition of Cr{sup 3+} ions. Electron paramagnetic resonance analyses of the sample confirm the presence of Cr{sup 3+} in the LiGa{sub 5}O{sub 8} matrix.

Structural characterization, thermoluminescence and EPR studies of Nd{sub 2}O{sub 3}:Co{sup 2+} nanophosphors

Nd2O3:Co2+ (1–4 mol%) nanophosphors (15–25 nm) have been prepared via low temperature solution combustion method. Scanning electron micrograph (SEM) shows that the product is highly porous in nature. The stokes line in the Raman spectrum at ∼2000 cm−1 is assigned to Fg mode and the anti-stokes lines are assigned to a combination of Ag + Eg modes. With increase of Co2+ concentration, the intensity of Fg mode decreases, whereas the combination of Ag + Fg modes completely disappears. Electron paramagnetic resonance (EPR) spectrum exhibits two resonance signals with effective g values at g = 2.25 and g = 2.03. Thermoluminescence (TL) response of Nd2O3:Co2+ nanopowders with γ dose 0.23–2.05 kGy was studied. The activation energy (E) and frequency factor (s) are estimated using Chens glow peak shape method and obtained to be in the range 0.45–1.67 eV and 1.8 × 104 to 4.0 × 1012 s−1, respectively. It is observed that the TL glow peak intensity at 430 K increases linearly with γ dose which is suitable for radiation dosimetry.

Structural characterization, EPR and thermoluminescence properties of Cd{sub 1−x}Ni{sub x}SiO{sub 3} nanocrystalline phosphors

Highlights: ► CdSiO{sub 3}:Ni{sup 3+} nanophosphorus have been prepared at much lower temperatures. ► Phosphors are well characterized by PXRD, TEM, FTIR and UV–Vis spectroscopy. ► EPR, thermo and photoluminescence properties were also reported. -- Abstract: Cd{sub 1−x}Ni{sub x}SiO{sub 3} (x = 1–7 mol%) nanophosphors have been prepared for the first time by the combustion method using oxylyldihydrizide as a fuel. Powder X-ray diffraction results confirm the formation of monoclinic phase. Scanning electron micrographs show that Ni{sup 2+} influences the porosity of samples. The optical energy gap is widened with increase of Ni{sup 2+} ion dopant. The electron paramagnetic resonance spectrum of Ni{sup 2+} ions in CdSiO{sub 3} exhibits a symmetric absorption at g = 2.343 and the site symmetry around Ni{sup 2+} ions is predominantly octahedral. The number of spins participating in resonance (N) and the paramagnetic susceptibility (χ) has been evaluated. The thermoluminescence intensity is found to increase up to ∼20 min ultra-violet exposure and thereafter, decrease with further increase of ultra-violet dose. The kinetic parameters such as activation energy (E), frequency factor (s) and order of kinetics was estimated using glow peak shape method and the results are discussed.