Up Converted Nanoparticles for Photonic Applications

The effects of the erbium concentration, crystal hosts and co-dopant on the up converted emission of Er3+ in oxide nanocrystals are reported. The effects of the Er3+ concentration and co-dopant (Yb3+) in the ZrO2 matrix on the up converted emission are reported. The presence of co-dopant (Yb3+) also increases the overall intensity of the up converted emission. A cw diode laser at 975 nm was used as a pump source for resonant sequential excitation of the I-4(11/2) and F-4(7/2) levels. Green and red up conversion emission at 550 nm and 670 nm were observed from these oxide nanocrystals with 975 nm excitation. The overall intensity decreases with an increasing concentration of erbium in different hosts. In up conversion emission intensity for the same concentration of Er ions, BaTiO3 host showed a highest up conversion emission intensity than that of ZrO2 and TiO2 host. The emission spectra and the pump intensity dependence of the luminescence intensities confirm that up converted emission in these materials is due to two-photon excited-state absorption (ESA) process

Synthesis and spectroscopic study of high quality alloy Cd<SUB>x</SUB>Zn<SUB>1-x</SUB>S nanocrystals

In the present study, we report the synthesis of high quality CdxZn1-xS nanocrystals alloy at 150°C with changing the composition. The shifting of absorption and emission peak in shorter wavelength is obtained with increasing the mole fraction of zinc. The quantum yield (QY) value decreases with increasing the Cd mole fraction and the values are 0.08, 0.13 and 0.40 for Cd0.62Zn0.38S, Cd0.52Zn0.48S and Cd0.31Zn0.69S nanocrystals, respectively after 120 min of reaction. However, the full width at halfmaximum (fwhm) values are 45, 34 and 28 nm and the corresponding quantum yield (QY) values are 0.52, 0.17 and 0.13 for 0.5 mM, 1.5 mM and 3 mM of initial S concentrations, respectively. It is interesting to note that the radiative decay time is dominating with increasing the Cd content. Analysis suggests that the decay dynamics depends on the composition of CdxZn1-xS nanocrystals

Photocatalytic properties of semiconductor SnO<SUB>2</SUB>/CdS heterostructure nanocrystals

Here we report the photocatalytic properties of semiconductor SnO2/CdS heterostructure nanocrystals. A type-II SnO2/CdS heterostructure has been synthesized from a single-source precursor and its structure was determined using XRD, HRTEM, elemental mapping and line scan EDAX analysis. A time resolved spectroscopic study revealed the effective charge separation in this heterostructure and the mechanism of charge separation was proposed using a schematic model. It is important to mention that the conductivity was found to be lower in the SnO2/CdS heterostructure compared to uncoated SnO2 nanorods due to efficient charge separation. The efficient charge separation in the SnO2/CdS heterostructure revealed its higher photocatalytic activity and the photocatalytic degradation of Congo red dye was found to be 97% and 20% for the SnO2/CdS heterostructure and SnO2 respectively under UV light irradiation

Sol-gel preparation of silica glass

This paper is a preliminary report on the preparation of silica glass containing very low amount of hydroxyl by the sol-gel processing technique. Gels were prepared from optimized amounts of tetraethyl orthosilicate, fumed silica and water. Acids and bases in small quantities were added for catalysing hydrolysis and adjusting the pH. Dried gels were heated up to 1400-degrees-C in various atmospheres to obtain transparent silica glass of the required density and very low (< 5 ppm) hydroxyl content

Study of photoluminescence properties of Er<SUP>3+</SUP> ions in SiO<SUB>2</SUB>–GeO<SUB>2</SUB> and Al<SUB>2</SUB>O<SUB>3</SUB> nanoparticles

We have used the sol–emulsion–gel method to prepare nanoparticles of SiO<SUB>2</SUB>, SiO<SUB>2</SUB>–GeO<SUB>2</SUB> and Al<SUB>2</SUB>O<SUB>3</SUB> doped by the same concentration Er<SUP>3+</SUP> ions for comparison. We have compared the luminescent efficiencies of these particles and we found that the luminescence spectra and lifetime of the excited state <SUP>4</SUP>&#8739;<SUB>13/2</SUB> of Er<SUP>3+</SUP> ions are found to be sensitive to the nature of host. A broad emission spectrum of width 58–55 nm peaked at wavelength of 1.5 μm and the decay times of <SUP>4</SUP>&#8739;<SUB>13/2</SUB>→<SUP>4</SUP>&#8739; <SUB>15/2</SUB> transition are 7.57 and 2.07 ms for 1000 °C heat-treated 1.0 mol% Er<SUP>3+</SUP> doped SiO<SUB>2</SUB>–GeO<SUB>2</SUB> and Al<SUB>2</SUB>O<SUB>3</SUB> nanoparticles, respectively. The analysis suggests that modification of relaxation mechanism is due to the nature of the host

Effect of crystal structure and concentration on luminescence in Er<SUP>3+</SUP>: ZrO<SUB>2</SUB> nanocrystals

The sol–emulsion–gel method is used for the preparation of Er3+ doped ZrO2 nanocrystals. The luminescence spectra and lifetime of the excited state 4&#8739;13/2 of Er3+ ions in ZrO2 nanocrystals are found to be sensitive to the crystal structure and dopant concentration. It is found that the luminescence lifetimes of 1.0 mol% Er3+ doped ZrO2 nanocrystals are 1.94 and 3.36 ms for 800 and 1000 °C heat-treated samples, respectively. The analysis suggests that modification of relaxation mechanism is due to the crystal structure of the host and concentration of ions

Optical fluorescence studies on sol-gel derived Pr doped silica glasses with added boron

Silica glasses containing Pr with or without boron as a co-dopant were prepared by the sol-gel method at 1100 degrees C. The influence of boron on the Pr doped glasses was studied by UV-visible-NIR, FTIR and fluorescence spectroscopies. The fluorescence intensity of the glasses increased significantly in the presence of boron. This was explained to be due to prevention of the cross relaxation process of these glasses

Study of rehydration process of alumina containing cerium doped silica gels by ultraviolet, visible and FTIR spectroscopy

Alumina containing Ce doped silica xerogel and glasses were prepared by sol-gel processing at 500-1000 degrees C under oxygen atmosphere. The partially densified gels were kept at 80% relative humidity for ageing and spectroscopic properties of the rehydrated partially densified gels were mainly studied by absorption and FTIR spectroscopy. With ageing time the generation of absorption bands of Ce3+ ions suggested the change of local symmetry of the Ce ions. Finally, fourfold splitting was observed for Ce3+ after 60 days indicating eight co-ordinated water complexes like dodecaheral complexes having symmetry group D-2d