Raja J. Amjad

Surface enhanced Raman scattering and plasmon enhanced fluorescence in zinc-tellurite glass

We report significant enhancements in Er(3+) luminescence as well as in Raman intensity in silver nanoparticles embedded zinc-tellurite glass. Surface enhanced Raman scattering effect is highlighted for the first time in tellurite glass containing silver NPs resulting in an enhanced Raman signal (~10 times). SAED manifest the growth of Ag(0) nanoparticles along the (111) and (200) crystallographic planes having average diameter in the range 14-36 nm. Surface plasmon resonance bands are observed in the range 484-551 nm. Furthermore, four prominent photoluminescence bands undergo significant enhancements up to 3 times. The enhancement is majorly attributed to the local field effect of silver NPs.

Optical Investigation of Sm3+ Doped Zinc-Lead-Phosphate Glass

Samarium doped lead-zinc-phosphate glasses having composition (60−x)P2O5-20PbO-20ZnO-xSm2O3 where x=0, 0.5, 1.0, 3.0mol% were prepared by using the melt quenching technique. The Archimedes method was used to measure their densities, which are used to calculate the molar volumes. The values of densities lie in the range 3.698–4.090 gm/cm3 whereas those of molar volume lie in the range of 37.24–40.00 cm−3. UV-vis-NIR absorption spectroscopy in the wavelength range 200–2000 nm was carried out. Absorption spectra consist of seven absorption peaks corresponding to the transitions from the 6H5/2 ground state to various excited energy levels. The energy band gap measured from the optical absorbance is found to be in the range of 3.88-4.43 eV and 3.68-4.33 eV for direct and indirect transitions, respectively. In addition, the photoluminescence spectrum shows four prominent emission bands centered at 560, 597, 642 and 700 nm corresponding to the 4G5/2−6HJ (J=5/2, 7/2, 9/2, 11/2) transitions respectively and the intensity of all the bands are enhanced as the concentration of Sm3+ ions increases.

Plasmon-Enhanced Upconversion Fluorescence in Er3+:Ag Phosphate Glass: the Effect of Heat Treatment

The melt quenching method is used to prepare erbium-doped silver nanoparticle (NP) embedded phosphate glass. The effect of annealing on the glass on the formation of silver NPs produced by the reduction of silver (Ag+ →Ag°) is studied. The glass samples are characterized by x-ray diffraction, UV-vis-NIR absorption, photoluminescence spectroscopy and transmission electron microscopy (TEM) imaging. The absorption spectra reveal not only the peaks due to Er3+ ions, but also the surface plasmon resonance band of silver NPs located around ~442 nm. The TEM imaging shows the homogeneous distribution of silver NPs of almost spherical shape with an average diameter of ~5 nm. Upconversion luminescence spectra show two major emissions at 550 and 638 nm, originating from the 4S3/2 and 4F9/2 energy levels of the Er3+ ions, respectively. The enhancement in the luminescence intensity of both the green and red bands is found to be due to the effective local field of the silver NPs as well as the energy transfer from the nanoclusters, comprised of centers with silver ions bound to silver atoms in dimers or trimers to Er3+ ions, whereas quenching occurred due to the energy transfer from erbium ions to silver NPs (Er3+ →Ag°).

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 ~1011 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, GeOx 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 × 1011 cm−2, respectively.

Enhanced green emission of terbium-ions-doped phosphate glass embedding metallic nanoparticles

Abstract. Tb3+-doped glasses are promising materials for green lasers working at a UV-excitation light. It is essential to find a commercially low-cost host with high quantum efficiency in the visible region. We report the preparation and optical characterization of a thermally stable and optically transparent phosphate glass containing silver nanoparticles with nominal composition 57P2O5-40(ZnO-PbO)-2Tb2O3-1AgNO3 (mol%) obtained by a melt-quenching technique and subsequent heat-treatments. The glasses are transparent in UV to near-infrared region and are not hygroscopic at ambient environment. The optical absorption and luminescence excitation spectra of the samples with and without silver nanoparticles are identical, and no sign of any silver species is revealed, while the luminescence spectrum is enhanced up to 1.7 times after heat-treating the samples for 15 h. The transmission electron microscopy and selected area diffraction pattern of glasses show the presence of silver nanoparticles with an average size of ∼15  nm and growth at [200] crystallographic direction. The lifetime of the D45 state of Tb3+ ions decreases from 3.06 to 2.85 ms by increasing the heat-treatment duration, which is indicative of the plasmonic effect of nanoparticles on the radiative rates of Tb3+-doped glasses.

Plasmon Assisted Luminescence in Rare Earth Doped Glasses

Incorporation of metallic nanoparticles in rare earth doped oxide glasses has been introduced as an interesting method to enhance their optical properties. Controlling the size and shape of metallic nanoparticles is a challenging issue which depends strongly and ambiguously on concentration, time and temperature of heat-treatments. In this chapter, we firstly revisit the importance of materials science in general and the rare-earth doped glasses in particular. The performance of rare earth ions in glassy matrices, the probable interactions and the related theories are discussed. Moreover, the incorporation of metallic nanoparticles and their effect on modification of optical properties of rare earth doped glasses is reviewed. Finally, several examples of enhancement and quenching of stokes and anti-stokes luminescence of rare earth ions doped in different glasses are summarized. The incorporation of the metallic nanoparticles is a promising method to improve the optical properties of different oxide glasses for diverse applications such as amplifiers, solid state lasers, sensors, etc. However, to understand the complete role of metallic nanoparticles and control their size distribution and shape, further research is necessary.

Germanium nanoislands grown by radio frequency magnetron sputtering: Annealing time dependent surface morphology and photoluminescence

Structural and optical properties of ~ 20 nm Ge nanoislands grown on Si(100) by radio frequency (rf) magnetron sputtering under varying annealing conditions are reported. Rapid thermal annealing at a temperature of 600°C for 30 s, 90 s, and 120 s are performed to examine the influence of annealing time on the surface morphology and photoluminescence properties. X-ray diffraction spectra reveal prominent Ge and GeO2 peaks highly sensitive to the annealing time. Atomic force microscope micrographs of the as-grown sample show pyramidal nanoislands with relatively high-density 1011 cm−2)). The nanoislands become dome-shaped upon annealing through a coarsening process mediated by Oswald ripening. The room temperature photoluminescence peaks for both as-grown 3.29 eV) and annealed 3.19 eV) samples consist of high intensity and broad emission, attributed to the effect of quantum confinement. The red shift (~0.10 eV) of the emission peak is attributed to the change in the size of the Ge nanoislands caused by annealing. Our easy fabrication method may contribute to the development of Ge nanostructure-based optoelectronics.

Lanthanide-Doped Zinc Oxyfluorotellurite Glasses

In this chapter, we present the versatile examples and optical properties of zinc oxyfluorotellurite glasses doped with rare earth ions, and current challenges in this field are discussed. Zinc-tellurite glasses are among the most important heavy metal glass compositions with a wide range of excellent structural, thermal, chemical, and optical properties. When doped with rare earth ions, zinc-tellurite glasses show superior properties than other glass compositions, such as wide broadband luminescence and efficient upconversion emissions of Er3+ ions, as well as high rare earth solubility, which facilitate the incorporation of sensitizers such as Ce3+ and Yb3+ ions. When modified with some fluoride components, the optical and thermal stability of rare-earth-doped zinc-tellurite glasses does not change drastically, while the average phonon energy stays in a low-range energy, and the excited state lifetime of the rare-earth ions increases due to the different site symmetry provided by F−1 ions rather than O−2 ions. The recent developments in the oxyfluorotellurite glasses doped with rare earth ions are given in this chapter, which will be compared to those achieved with the zinc-tellurite oxide glasses.

Plasmon enhanced scattering and fluorescence in amorphous matrix

Abstract A melt-quench method is used to synthesize a series of tellurite glasses containing fixed concentration of Er2O3, with and without silver nanoparticles. The existence of metallic nanoparticles (average diameter ∼24–36 nm) inside the glass is confirmed by transmission electron microscope imaging. From UV–Vis absorption spectroscopy, a surface plasmon resonance band is detected in the visible region (∼484 nm). Furthermore, the intensity of both fluorescence and Raman scattering is found to be enhanced by embedding silver nanoparticles inside the glass matrix. These enhancements are attributed to the surface plasmon resonance effect in which direct plasmon excitation enhances the local field at the surface of the nanostructures. Enhanced fluorescence influenced by silver nanoparticles may contribute towards the development of optical displays, laser and optical memory devices whereas amplification of the Raman signal is promising for Raman amplifiers.

Enhanced infrared to visible upconversion emission in Er3+ doped phosphate glass containing silver nanoparticles

Phosphate glasses containing fixed concentration of rare-earth with and without metallic nanoparticles (NPs) having compositions (59.5-x) P2O5-MgO-xAgCl-0.5Er2O3, where 0 ≤ x ≤ 1.5 mol% was prepared using melt-quenching technique. Spectral characterizations were made using UV-VIS-IR spectroscopy and photoluminescence spectroscopy. Addition of silver NPs enhanced the corresponding absorption and was optimum at 1.5 mol% AgCl. Infrared to visible frequency upconversion (UC) emission were observed in the glass on pumping with 797 nm radiation. Furthermore, it was found that the emission at 540 nm, due to Er3+transition (4S3/2-4I15/2) was much more influenced by the silver NPs in comparison to the emission at 632 nm (4F9/2 - 4I15/2). These enhancements were attributed to the local fields present in the vicinity of silver NPs. Moreover, the rapid increase in the intensity of the green band as compared to the red band was due to the charge cloud effect of the plasmon band. Since green band lie more close to the plasmon frequency band of Ag and hence showed rapid increase compared to the far lying red bands. Our findings may contribute towards the development of solid state laser and sensors