Spectroscopic investigation and Judd-Ofelt analysis of silver nanoparticles embedded Er3+-doped tellurite glass

A series of silver nanoparticles (NPs) embedded zinc-tellurite glass is prepared by melt-quenching technique. The transmission electron microscopic images reveal spherical as well as anisotropic silver NPs having average diameter in the range of 14-48 nm. The Er3+-free glass sample containing AgCl exhibits surface plasmon resonance (SPR) band of Ag NPs centered at ~ 501 nm. From Judd-Ofelt analysis, it is found that by increasing the concentration of NPs, the value of O2 is enhanced suggesting increased covalency and decreased symmetry around the Er3+ ions. Integrated emission cross-section (IEC) is enhanced as the concentration of silver NPs is increased up to 0.5 mol% AgCl. Fourier infrared spectra show that the intensity of the vibrational band of the water molecule and fundamental stretching band of OH group are suppressed. Furthermore, under an excitation wavelength of 786 nm, three prominent upconversion emissions are observed at 520 nm, 550 nm and 650 nm which are attributed to 2H11/2, 4I15/2, 4S3/2, 4I15/2, and 4F9/2, 4I15/2 transitions, respectively. The upconversion emissions are enhanced significantly by introduction of silver NPs. The enhancement is mainly attributed to the local field effect of silver NPs. Studied nanocomposites are potential candidates for the development of solid state lasers

Up-conversion enhancement in Er 3 +-Ag co-doped zinc tellurite glass: Effect of heat treatment

The melt quenching method was used to synthesize the Ag 0 nanoparticles and Er 3 + ions co-doped zinc tellurite glass. The glasses were characterized by differential thermal analyzer, UV-VIS-IR absorption, photoluminescence spectroscopy and TEM imaging. Heat treatment at different annealing time intervals above the glass transition temperature was applied to reduce the Ag + ions to Ag 0 NPs. The influence of heat treatment on structural and optical properties is examined. Intense and broad up-conversion emissions of silver are recorded in the visible region. Up-conversion luminescence spectra revealed three major emission peaks at 520, 550 and 650 nm originating from 2H 11/2, 4S 3/2 and 4F 9/2 levels, respectively. An efficient enhancement in visible region is observed for samples containing silver NPs. The absorption plasmon peaks are evidenced around 560 and 594 nm. The effect of localized surface plasmon resonance and the energy transfer from the surface of silver NP to trivalent erbium ions are described as the sources of enhancement. © 2012 Elsevier B.V. All rights reserved

Chemical durability and thermal stability of ER3+-doped zinc tellurite glass containing silver nanoparticles

Improving the chemical durability and thermal stability of rare-earth doped glasses is a challenging issue. Glasses with composition (80-x)TeO2-20ZnO-1Er2O3-xAgCl (x=0, 0.5, 1, 2 and 3 mol%) were prepared by melt quenching method. The chemical durability and water resistivity of those glasses are investigated by measuring the weight of samples after and before weathering by water and ammonium hydroxide. Variation of surface morphology is observed by AFM, SEM and EDX techniques. The weight loss is explained in terms of dissolution of glass in the immersed solution. Increments in the weight of samples are attributed to clustering and deposition of elements on the glass surface. The weight loss over twenty one days showed that addition of AgCl decreases the resistivity against water and ammonium solution. The introduction of AgCl found to increase the thermal stability and resulted in stronger glass networks. Also, the fragility is improved by incorporation of AgCl as revealed by the broadening of glass transition width. Our observation may be useful for the fabrication of nanophotonic devices in different environment

A model for enhanced up-conversion luminescence in erbium-doped tellurite glass containing silver nanoparticles

Nanoparticles (NPs) size dependent enhancement of the infrared-to-visible frequency upconversion (UC) and absorption coefficient in silver NPs embedded Er3+ doped tellurite glasses on pumping with the 976 nm radiation are investigated. Rate equations are derived by developing a comprehensive 4-level model in integrating the effects of quantum confinement (QC) and local field of silver NPs. Considering the spherical NPs size distribution as Gaussian, an analytical expression for the luminescence intensity and absorption coefficient are obtained for the first time. An enhancement in UC emission intensity of the green bands (2H11/2?4I15/2 and 4S3/2?4I15/2) and red band (4F9/2?4I15/2) emission of Er3+ ion at temperature 250 K and at optimized Er3+ concentration 1.0 mol% is observed up to few times in the presence of silver NPs. Furthermore, the green emission shows larger enhancement than the red emission. The observed of Er3+ luminescence is mainly attributed to the local field effects namely the surface plasmon resonance of silver NPs that causes an intensified electromagnetic field around NPs, resulting in enhanced optical transitions of Er3+ ions in the vicinity. The model is quite general and can be applied to other rare earth doped glasses containing metallic NPs. Our results on NPs size dependent emission intensity and absorption coefficient are in conformity with other findings. The present systematic study provides useful information for further development of UC lasers and sensors

Photoluminescence study of Sm3+-Yb3+ co-doped tellurite glass embedding silver nanoparticles

We report on the upconversion emission of Sm3+ ions doped tellurite glass in the presence of Yb3+ ions and silver nanoparticles. The enhancement of infrared-to-visible upconversion emissions is achieved under 980 nm excitation wavelength and attributed to the high absorption cross section of Yb3+ ions and an efficient energy transfer to Sm3+ ions. Further enhancements are attributed to the plasmonic effect via metallic nanoparticles resulting in the large localized field around rare earth ions. However, under excitation at 406 nm, the addition of Yb3+ content and heat-treated silver nanoparticles quench the luminescence of Sm3+ ions likely due to quantum cutting and plasmonic diluent effects, respectively

Structural and optical behavior of germanium quantum dots

Controlled growth, synthesis, and characterization of a high density and large-scale Ge nanostructure by an easy fabrication method are key issues for optoelectronic devices. Ge quantum dots (QDs) having a density of ∼10 11 cm -2 and a size as small as ∼8 nm are grown by radio frequency magnetron sputtering on Si (100) substrates under different heat treatments. The annealing temperature dependent structural and optical properties are measured using AFM, XRD, FESEM, EDX, photoluminescence (PL) and Raman spectroscopy. The effect of annealing is found to coarsen the Ge QDs from pyramidal to dome-shaped structures as they grow larger and transform the nanoislands into relatively stable and steady state configurations. Consequently, the annealing allows the intermixing of Si into the Ge QDs and thereby reduces the strain energy that enhances the formation of larger nanoislands. The room temperature PL spectra exhibits two strong peaks at ∼2.87 eV and ∼3.21 eV attributed to the interaction between Ge, GeO x and the possibility of the presence of QDs core-shell structure. No reports so far exist on the red shift ∼0.05 eV of the strongest PL peak that results from the effect of quantum confinement. Furthermore, the Raman spectra for the pre-annealed QDs that consist of three peaks at around ∼305.25 cm -1, 409.19 cm -1 and 515.25 cm -1 are attributed to Ge-Ge, Ge-Si, and Si-Si vibration modes, respectively. The Ge-Ge optical phonon frequency shift (∼3.27 cm -1) associated with the annealed samples is assigned to the variation of shape, size distribution, and Ge composition in different QDs. The variation in the annealing dependent surface roughness and the number density is found to be in the range of ∼0.83 to ∼2.24 nm and ∼4.41 to ∼2.14 × 10 11 cm -2, respectively

Eu3+ and Ce3+ co-doped aluminosilicate glasses and transparent glass-ceramics containing gahnite nanocrystals

Transparent zinc-aluminosilicate glass-ceramics containing cerium and europium ions were prepared by controlled thermal heating of parent glasses. Addition of CeO2 resulted in the improved transparency of the glasses in the visible spectral region: X-ray diffraction patterns of the glass-ceramics indicate the formation of the crystalline gahnite phase and there are evidences of Ce3+ and Eu3+ occupancies in this phase, as well as co-existence in the amorphous phase. Ce3+ emission corresponding to the allowed f-d transitions is identified, as well as an anomalous emission in the red-infrared region. The characteristic luminescence of Eu3+ in the red is observed. Judd-Ofelt analysis of Eu3+-doped samples reveals enhanced site asymmetry around the ion and a high branching ratio for the 612 nm emission after ceramization. Due to enhanced Ce3+ emission and Eu3+ emission quenching, color tunability is possible in the red to blue spectral region, depending on the heat treatment duration. (C) 2017 Elsevier B.V. All rights reserved

Silver nanoparticles enhanced luminescence of Eu3+-doped tellurite glass

A series of silver nanoparticles (NPs) embedded zinc-tellurite glass is prepared by the melt-quench method. In order to nucleate and reduce the silver ions (Ag+) to silver NPs (Ag0) heat treatment with different time intervals above the glass transition temperature is carried out. The transmission electron microscopy (TEM), differential thermal analyses (DTA), UV-vis-NIR absorption spectroscopy and photoluminescence (PL) spectroscopy are used to study the annealing time dependent optical properties. The glass transition temperature (Tg) from DTA for an as prepared sample is 296 °C. TEM image displays the homogeneous distribution of silver NPs with average diameter ~8 to 27 nm. From UV-vis-NIR spectra, the observed localized surface plasmon resonance (LSPR) bands are found to be located within the range 487-501 nm for the samples with AgCl. Furthermore, under an excitation of 395 nm, four bands are observed at 585, 612, 650, 698 nm which corresponds to the 5D0-7F0;1;2;3;4 transitions of Eu3+ ions. Moreover, luminescence intensity of all the bands is increased due to the presence of silver nanostructures. The hypersensitive transition 5D0-7F2 of Eu 3+ is much more enhanced (∼ 1.9 times) mainly due to the local field effect of silver NPs

Enhanced frequency up-conversion in er3+-doped sodium lead tellurite glass containing silver nanoparticles.

A series of silver nanoparticle embedded in erbium-doped tellurite glasses were synthesized using a one step melt-quenching method. Density and refractive index of glasses were measured. Thermal and optical characterizations were performed and plasmon bands of elliptical nanoparticles were observed. An enhancement of green (525 and 550 nm) and red (632 nm) lines in luminescence spectra of Er3+-doped silver-embedded tellurite glass was recorded and explained by energy transfer mechanism from silver nanoparticles to erbium ion in addition to enhanced local field in vicinity of metallic nanoparticles in the glass. The presence of nanoparticles was confirmed by transmission electron microscopy imaging and reduction of silver ions to silver neutral particles discussed through the redox potential estimation in probable reactions. Silver-erbium co-doped tellurite glass exhibits strong novel optical properties which nominate it as the promising glass for laser, color displays, and photonic applications