Surface modification of bulk n-InAs (111)A etched in bromineemethanol

N. Eassa,R. Betz,E. Coetsee,H.C. Swart,A. Venter,J. R. Botha 한국물리학회 2013 Current Applied Physics Vol.13 No.2

X-ray photoelectron spectroscopy, field emission scanning electron microscopy, Raman and photoluminescence spectroscopy were used to evaluate the surface properties of n-type InAs (111)A etched in a 1% Bremethanol solution. Etching completely removes the native oxides from the surface and enhances the photoluminescence response. The adsorption of bromine onto the InAs surface leads to the formation of IneBrx and AseBrx bonds (x ¼ 1, 2, 3) as inferred from changes in the In 3d3/2;5/2 and As 3d core level binding energies. The etch rate is found to decrease due to strong anisotropic effects and the high volatility of the bromine species. A 1 min Bremethanol etch was found to enhance the photoluminescence intensity by a factor of 3, probably due to a reduction in the surface state density upon deoxidation of the surface. This is thought to be due to reductions in the surface state density. The presence of native oxides enhances both the surface accumulation layer and the surface state density.

Enhanced green emission from UV down-converting Ce³⁺-Tb³⁺ co-activated ZnAl₂O₄ phosphor

Tshabalala, K.G.,Nagpure, I.M.,Swart, H.C.,Ntwaeaborwa, O.M.,Cho, S.-H.,Park, J.-K. American Institute of Physics 2012 Journal of Vacuum Science & Technology. B Vol.30 No.3

Violet-blue-shift of emission and enhanced luminescent properties of Ca3(PO4)2:Ce3+ phosphor induced by substitution of Gd3+ ions

L. Reddy,T.J. Nkosi,P.L. Masiteng,A. Balakrishna,H.C. Swart,O.M. Ntwaeaborwa 한국물리학회 2020 Current Applied Physics Vol.20 No.5

Ca3(PO4)2:1mol%Ce3+/xGd3+ (where x = 0.5, 1.0, 3.0 and 5.0 mol%) phosphors were synthesized by the conventional combustion synthesis method. The X-ray diffraction patterns showed their rhombohedral structure with space group of R3c. The optical properties including reflectance, excitation and emission were investigated. The band gaps of the phosphors were calculated from diffuse reflectance spectra data using the Kubelka–Munk function. The photoluminescence (PL) excitation spectra exhibited the broadband 4f–5d transition of Ce3+ ions centered at ~265 nm. The PL emission properties of the Ca3(PO4)2:Ce3+/Gd3+ phosphors were studied as a function of the Gd3+ ion concentration. The Ca3(PO4)2:Ce3+/Gd3+ phosphor had a wide emission band ranging from 320 to 400 nm, and peaking at 365 nm. This emission is ascribed to the transition from the higher 5d band to 2F7/2, 2F5/2 states of the Ce3+ ion. The 365 nm peak shifted to longer wavelengths with increasing concentration of the Gd3+ ion. The CIE chromaticity diagram of Ca3(PO4)2:Ce3+/Gd3+ phosphor showed tunable emission colour from violet to violet-blue, suggesting that this phosphor can act as a source of violet-blue colour for application in information displays, phototherapy and photoluminescent liquid crystal displays.

Role of silver doping on the defects related photoluminescence and antibacterial behaviour of zinc oxide nanoparticles

Kumar, Vinod,Prakash, Jai,Singh, Jitendra Pal,Chae, Keun Hwa,Swart, C.,Ntwaeaborwa, O.M.,Swart, H.C.,Dutta, Viresh Elsevier 2017 Colloids and surfaces Biointerfaces Vol.159 No.-

<P><B>Abstract</B></P> <P>The Ag doped ZnO (ZnO:Ag) NPs with a hexagonal wurtzite structure were synthesized by a solution combustion method. X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) were used to study the defects, local electronic and atomic structures before and after Ag doping. XPS and XANES studies confirmed the deficiency of concentration of defects in ZnO after Ag doping. The photoluminescence study showed the deep level emission in the orange-red region in addition to the band to band emission. It was also found that the defect related emission of ZnO was decreased with an increasing in Ag concentration. The antibacterial behaviour of ZnO and ZnO:Ag NPs was studied against the gram positive and gram negative bacteria. The role of Ag doping and defects in the ZnO NPs were discussed for the observed antibacterial and photoluminescence behaviour.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ag doped ZnO. </LI> <LI> Antibacterial study. </LI> <LI> XANES and XPS analysis. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Luminescence investigations on LiAl_5O_8:Tb^3+ nanocrystalline phosphors

Shreyas S. Pitale,Vinay Kumar,Indrajit Nagpure,O.M. Ntwaeaborwa,H.C. Swart 한국물리학회 2011 Current Applied Physics Vol.11 No.3

Tb^3+-doped porous LiAl_5O_8 nanophosphors were successfully synthesized using a single step combustion method. Structural characterization of the luminescent material was carried out with X-ray diffraction (XRD) analysis and high resolution transmission electron microscopy (HRTEM). Surface composition was estimated from X-ray photoelectron and Auger spectroscopic techniques. The average particle size was estimated as 37 ± 3 nm. Luminescence properties were studied by the photoluminescence spectroscopy. The phosphor showed intense luminescence in the green region due to the magnetic dipole transition of 5^D_4→7^F_5 of the Tb^3+ ion at 543 nm under 241 nm excitation. The intense 4f―4f transitions of Tb^3+outshine the luminescence from host which would otherwise deteriorate the color quality of the display device under operation.

A novel orange-red emitting Ba2Ca(BO3)2:Sm3+ phosphor to fill the amber gap in LEDs: Synthesis, structural and luminescence characterizations

M. Manhas,Vinay Kumar,Vivek K. Singh,J. Sharma,Ram Prakash,Vishal Sharma,A.K. Bedyal,H.C. Swart 한국물리학회 2017 Current Applied Physics Vol.17 No.11

The present paper reports on the structural and luminescent properties of un-doped and Sm3þ doped Ba2Ca(BO3)2 phosphors synthesized by the conventional solid state method. For structural characterizations, the X-ray diffraction, FTIR spectroscopy and Rietveld refinement method were used. The FTIR spectrum was composed of basic BO3 and BO4 structural units of borates. The Sm3þ doped phosphors under 402 nm (6H5/2/4L13/2) excitation, showed an orange red emission corresponding to the 601 nm (4G5/2 / 6H7/2) transition of the Sm3þ ion. An increase in the PL emission intensity was observed up to 2 mol % with the increase in Sm3þ ions concentration. The critical distance between the Sm3þ e Sm3þ ions were found to be 24.36 Å. Moreover, the phosphors decaytime and optical bandgap at different concentration of Sm3þ ion also have been discussed in details. All the results show that Ba2Ca(BO3)2:Sm3þ phosphor may be used with a near ultraviolet (n-UV) chip to fill the amber gap in light emitting diodes (LEDs).

Optical and surface enhanced Raman scattering properties of Au nanoparticles embedded in and located on a carbonaceous matrix

Prakash, Jai,Kumar, Vinod,Kroon, R. E.,Asokan, K.,Rigato, V.,Chae, K. H.,Gautam, S.,Swart, H. C. The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.4

<P>Au nanoparticles (NPs) on the surface and embedded in a matrix have been the subject of studies dealing with a variety of spectroscopic and sensing applications. Here, we report on low energy Ar ion induced evolution of the morphology of a thin Au film on a polyethylene terephthalate (PET) substrate along with thermodynamic interpretations, and corresponding unique surface plasmon resonance (SPR) and photoluminescence (PL) properties. These properties are linked to the variation of surface nanostructures and the surface enhanced Raman scattering (SERS) effect of methyl orange (MO) dye molecules adsorbed on the surface. Ion induced thermal spike and sputtering resulted in dewetting of the film with subsequent formation of spherical NPs. This was followed by embedding of the NPs in the modified PET due to the thermodynamic driving forces involved. The surface and interface morphologies were studied using atomic force microscopy and cross-sectional transmission electron microscopy. X-ray photoelectron spectroscopy was used to study the chemical changes in the system upon irradiation. The optical properties were studied by diffuse reflectance UV-Vis spectroscopy and PL using a 325 nm He-Cd laser. The red shift of the SPR absorption and the blue shift of the PL emission have been correlated with the surface morphology. The blue PL emission bands at around 3.0 eV are in good agreement with the literature with respect to the morphological changes and the blue shift is attributed to compressive strain on the embedded Au NPs. Enhancement of the SERS signals is observed and found to be correlated with the SPR response of the Au nanostructures. The SERS analyses indicate that MO molecules may be adsorbed with different orientations on these surfaces i.e. Au NPs located on the surface or embedded in the modified PET. These polymeric substrates modified by NPs can have a potential application in solid-state light emitting devices and can be applied in SERS based sensors for the detection of organic compounds.</P>