Optical Investigation of Sm^(3+) Doped Zinc-Lead-Phosphate Glass

Samarium doped lead-zinc-phosphate glasses having composition(60-x)P_(2)O_(5)-20PbO-20ZnO-xSm_(2)O_(3) 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/cm^(3) 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.

Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots

The influences of thermal annealing on the structural and optical features of radio frequency（rf） magnetron sputtered self-assembled Ge quantum dots（QDs） on Si（100） are investigated.Preferentially oriented structures of Ge along the（220） and（111） directions together with peak shift and reduced strain（4.9%to 2.7%） due to post-annealing at 650 ℃ are discerned from x-ray differaction（XRD） measurement.Atomic force microscopy（AFM） images for both pre-annealed and post-annealed（650 ℃） samples reveal pyramidal-shaped QDs（density - 0.26×10^11 cm^-2） and dome-shape morphologies with relatively high density - 0.92×10^11 cm^-2,respectively.This shape transformation is attributed to the mechanism of inter-diffusion of Si in Ge interfacial intermixing and strain non-uniformity.The annealing temperature assisted QDs structural evolution is explained using the theory of nucleation and growth kinetics where free energy minimization plays a pivotal role.The observed red-shift - 0.05 eV in addition to the narrowing of the photoluminescence peaks results from thermal annealing,and is related to the effect of quantum confinement.Furthermore,the appearance of a blue-violet emission peak is ascribed to the recombination of the localized electrons in the Ge-QDs/SiO2 or GeOx and holes in the ground state of Ge dots.Raman spectra of both samples exhibit an intense Ge-Ge optical phonon mode which shifts towards higher frequency compared with those of the bulk counterpart.An experimental Raman profile is fitted to the models of phonon confinement and size distribution combined with phonon confinement to estimate the mean dot sizes.A correlation between thermal annealing and modifications of the structural and optical behavior of Ge QDs is established.Tunable growth of Ge QDs with superior properties suitable for optoelectronic applications is demonstrated.

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 （rI） magnetron sputtering under varying annealing conditions are reported. Rapid thermal annealing at a temperature of 600 ℃ 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 （～ 10^11 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.

Plasmon-Enhanced Upconversion Fluorescence in Er^(3+):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^(o))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 Er^(3+)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 4S_(3/2)and 4F_(9/2)energy levels of the Er^(3+)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 Er^(3+)ions,whereas quenching occurred due to the energy transfer from erbium ions to silver NPs(Er^(^(3^(+)))→Ag^(o)).

Growth of Ge/Si(100) Nanostructures by Radio-Frequency Magnetron Sputtering: the Role of Annealing Temperature

Surface morphologies of Ge islands deposited on Si(100) substrates are characterized and their optical properties determined.Samples are prepared by rf magnetron sputtering in a high-vacuum chamber and are annealed at 600℃,700℃ and 800℃ for 2 min at nitrogen ambient pressure.Atomic force microscopy,field emission scanning electron microscopy,visible photoluminescence (PL) and energy dispersive x-ray spectroscopy are employed.The results for the annealing temperature-dependent sample morphology and the optical properties are presented.The density,size and roughness are found to be strongly influenced by the annealing temperature.A red shift of ~0.29 eV in the PL peak is observed with increasing annealing temperature.

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,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.

Physical, structural and optical studies on magnesium borate glasses doped with dysprosium ion

Intense visible emissions from dysprosium(Dy3+) ions doped glasses became prospective for diverse technological applications. In this paper, physical, optical and structural properties of magnesium borate glasses doped with varied concentrations of DyOwere examined. Such glasses were synthesised by melt quenching method and characterized at room temperature using several analytical techniques.Luminescence and absorption spectra(in the visible region) of as-quenched samples were used to evaluate the physical and optical properties. XRD pattern confims the amorphous state of as-quenched samples. The Fourier transform infrared(FTIR) spectra of glasses reveal various bonding vibrations assigned to different functional groups. UV-vis-NIR spectra disclose eight absorption bands accompanied by a band for hypersensitive transition positioned at 1260 nm(~6 H→~6 F). The values of direct and indirect optical energy band gap of the studied glasses are decreased with the increase of Dyion contents. The photoluminescence spectra of all glasses under the excitation of 380 nm display two prominent emission bands centred at 497 nm(~4 F→~6 H, blue) and 587 nm(~4 F→~6 H, green).The achieved intense luminescence from the proposed glass composition may be beneficial for solidstate laser applications.

Spectral investigation of Sm^(3+)/Yb^(3+) co-doped sodium tellurite glass

Sm3＋/yb3＋ co-doped tellurite glasses are prepared by melt-quenching technique. The density of the glasses varies between 4.65 and 4.84 g/cm3. The optical absorption spectra consist of eight bands in the wavelength range of 350-2 000 nm, which correspond to the transitions from ground level 6H5/2 to the various excited states of the Sm3＋ ion. Energy band gaps vary in the range of 2.73 2.91 eV, and the Urbach energy ranges from 0.21 to 0.27. Emission spectra exhibit four peaks originating from the 4G5/2 energy level centered at 576, 613, 657, and 718 nm. Quenches in emission bands may be due to the energy transfer from the Sm3＋ to Yb3＋ ions.