Effect of Europium (III) Oxide doping on the nanoscale ceramic Stannates(MSnO3) of Ca, Ba upon photo luminescence, catalytic degradation and anti-microbial activity – Green approach

The study of alkaline earth doped stannate ceramics of Barium and Calcium is being carried out to explore more on the phosphorescent applications. The present study is an energy and cost-efficientgreen approach towards the preparation of Europium (III) doped stannate of Calcium and Barium in the nano scaleas it involves the biowaste of egg shell as a precursor for calcium carbonate and the plant extract of aloe vera as the reaction medium and a comparatively lower calcination temperature than reported so far. The structure, phase purity, surface morphology and applications in terms of photo luminescence, photo catalytic and anti-microbial activities have been investigated. The doping of alkaline earth metal of Europium in lower weight percentage(lesser than one) was carried out at lower processing temperatures than reported earlier. There was a phase transition in the case of barium stannate upon doping and there were observable changes in crystallite size, morphology and microstructure in the case of Stannates of Calcium and Barium. The results of photo luminescence study and the photo catalytic degradation of methylene blue dye were encouraging. The anti-microbial study in terms of toxicity of the doped samples in smaller dosages upon Pseudomonas aeruginosa, Staphylococcus aureus provided a new dimension to their application. article history Received: 22 May 2018 Accepted: 02 August 2018


Introduction
The compound [M=Ca, Ba] MSnO 3 belongs to the family of perovskite type alkaline earth stannates which have attractive dielectric characteristics, excellent optical and semiconducting properties.The Stannates also exhibit high band gap [3.0-3.6eV],high melting point and is stable which offers many advantages and applications.The Stannates also find their applications in display phosphor matrix, ceramic materials, thermally stable capacitors in electronic industry, lithium ion batteries, thermally stable capacitors, photo catalytic utilization and gas sensor hosts .The important luminescence properties of rare earth ions doped in perovskite electronic has become attractive during the past decade, not only for its use as a probe to investigating local centers and energy migration processes in the microstructures of electronic materials but also in the search of novel phosphors for display technologies.Among them, ABO 3 (A = Ca, Sr and B) B = Ti, Zr, Si, Nb, hf, etc) activated by rare earth ions, including Sm 3+ , Eu 3+ , Pr 3+ , Ce 3+ , Tb 3+ , Er 3+ 1 .They are important materials in the electronic industry and their synthetic methods can modify their structure and hence properties.The double oxide materials of the type ABO 3 are found to be thermally stable upto 2000 o C with semiconducting properties and the powders can be sintered into a solid mass 2 .Phosphors are the highly purified inorganic materials doped with small impurities or additives or quencher called dopants or activator which is usually present in a very low concentration vary from a few ppm up to 5mol %of the host lattice.Some phosphors contained more than one activators and the term co-activators is used in such cases.for example, inorganic phosphors, mostly Europium is the main active centre to produce luminescence and supported by lanthanum, gadolinium, neodymium, dysprosium etc can be used as co-activators as per the phosphor requirement.Europium doped nanophosphors are very important materials and widely used in plasma displays, three colored lamps and luminescent paints etc 3 .In this context, exploring the factors which will contribute towards energy and cost effective synthetic approaches for the preparation of stannate ceramics with enhanced properties has become significant.In the present study bio waste of egg shell as a precursor, plant extract as the medium and lower calcination temperature have been considered for the preparation of stannate ceramic.Further investigation on the doping of lower percentage of alkaline earth metal of Europium on the as synthesized ceramic sample has been carried out to study its effect on the structure, morphology leading to its effect on the enhancement of the photo luminescence, catalytic and anti-microbial properties.

%d =100 *{initial absorbance -absorbance at time 't'}/initial absorbance antibacterial activity using agar well diffusion method
The synthesized samples was screened for antibacterial activity against human pathogens such as Pseudomonas aeruginosa, Staphylococcus aureus using agar well diffusion method.The samples were prepared by dissolving the 10mg

Structural Characterization
The prepared nano samples were subjected to micro structural characterization.The parameters crystallite size, nature of the metal bonding and impurities, surface morphology, were examined using uV -Visible spectra, Powder X-ray diffractograms (PXRD), Fourier Transformed Infra-red (FTIR-ShIMADZu)spectra, Scanning Electron microscopic images along with the elemental composition on the surface (SEM-hITAChI S 3400N -EDAX), Photo luminescence (Pl-Cary 100 (Varian)) spectra respectively.The percentage degradation efficiency of the as synthesised samples upon Methylene Blue dyewas studied using SChIMADZu 1601 spectrophotometer in 400 to 800 nm range.The FTIR spectra were collected in the frequency range 4000 to 400 cm -1 against the background of KBr.The PXRD pattern for the samples were recorded using CuKα radiation with a diffraction angle between 10 and 70.The crystallite size "D" calculated using the   4 .The peak 1426.42-1448cm-1 was due to the presence of undissociated carbonates based on the report of 5 .The broad band in the region 3400-3600cm-1 was due to the stretching vibrations of Oh group which was correlated with the report of 6 .

Ft-Ir Spectrum of Eu 3+ doped nanoscale Barium Stannate Ceramic
In all the three Europium doped Barium stannate samples, the peak observed at 650-655.00 cm -1 was due to Sn-O-Sn stretching vibrations which was correlated well with the reports of 7 .The peak at 1446-1452.46cm-1 were due to the stretching frequency of inorganic carbonate which correlated with the observations of 8,9 .The broad band in the region 3413.19-3436.33cm -1 and were due to the stretching vibrations of Oh group.In the present study, the average crystallite size of calcium stannate was found to be 32nm.Also, the peak due to SnO was absent and hence it could be concluded that aloe vera played an important role in oxidizing Sn (II) to Sn (IV) which was correlated well with the report of 11 .There was no peak corresponding to Eu 2 O 3 in the PXRD spectrum which correlated well with the FTIR results.This is contrary to the reports of M. Ayvacikli 11 where in the presence of orthorhombic structure for Europium doped barium stannate was identified with the crystallite size of >30 micrometer.Also, the ceramic was synthesized by sol by the solid-state method with the sintering temperature of 1400°C.The peak due to SnO was absent and hence it could be concluded that aloe vera played an important role in oxidizing Sn (II) to Sn (IV) which was correlated well with the report of 11

Scanning Electron Microscopy Image [SEM] SEM Images of Eu 3+ doped nanoscale Calcium Stannate Ceramic
The surfacemorphological examination of nano scale tin (IV) oxide prepared using aloe vera plant extract and Eu 3+ doped nanoscale calcium stannate ceramic as given by SEM images

SEM images of Eu 3+ doped nanoscale Barium Stannate Ceramic
The surface examination of Eu 3+ doped nanoscale barium stannate ceramic as given by SEM images (Figure-8 (a) BaSnO 3 :0.25% Eu 3+ ) showed., near spherical, stick and rod like structure with agglomeration of particles.The stick morphology of the sample was reported at higher calcinations temperatureof 1200°C and was due to the presence of barium carbonate [8], [9].In the sample of (b) BaSnO3:0.50%Eu 3+ there were more rod like structures and near spherical due to increasing percentage of Eu 3+ on the stannate surface.In the sample of (c)BaSnO3:0.75%Eu 3+ there was welldeveloped spherical crystallites with lesser rod like structures.These observations clearly indicated the effect of doping fractional percentages of rare earth ions on the surface morphology and hence the surface properties of the ceramics.however, the SEM images were supportive of the PXRD results.

Energy dispersive X-ray analysis (EdaX)
The relative Europium percentage of elements on the surface identified by SEM images was shown in the  In the Pl spectra of CaSnO 3 :0.25%Eu 3+ there were emission bands observed at 407.07 nm, 420.00 nm, 485.07 nm and 518.05 nmas shown in Figure -9.There were two sharp and twobroad emission bands were observed while in the sample CaSnO 3 :0.50%Eu 3+ there were emission bands observed at 407.07 nm, 420.00 nm, 485.07 nm and 518.05 nm.In the sample CaSnO 3 : 0.75% Eu 3+ there were the emission bands were observed at 406.00 nm 420.00 nm and 518.05 nmas shown in figure and the reports were correlated 10 .All the emission spectra were observed in visible region.Anyhow the extent to which the intensity photoluminescence Spectrum of Eu 3+ doped nanoscale Barium Stannate Ceramic Photolumine scence study of the nanoscale Barium stannate ceramic was carried out with the excitation wavelength of 380 nm and following observations were made.In the sample of BaSnO 3 : 0.25% Eu 3+ there were emission bands observed at 407.07 nm 420.00 nm, 485.07 nm and 518.05 nm for the sample as shown in Figure -10.There are two sharp and two broad emission bands were observed.In the sample BaSnO 3 : 0.50 % Eu 3+ there Emission bands observed at 407.07 nm, 420.00 nm, 485.07 nm and 518.05 nm for the sample as shown in figure.There are two sharp and two broad emission bands were observed.BaSnO 3 : 0.75 % Eu 3+ there were emission bands observed at 407.07 nm 420.00 nm 485.07 nmand 518.05 nm for the sample as shown in

Conclusion
In the present study, a simple and energy effective process of introducing the rare earth metal of Eu 3+ ion into the Stannates of Ca and Ba which were prepared by an energy effective green method was investigated.A lower percentage of less than one by weight of Europium with respect to the stannate samples was doped and the effect was considered in terms of its Photo luminescence and degradative property upon the organic dye of Methylene Blue.The microstructure, surface morphology of the samples were correlated with the luminescence and catalytic property.There was a drastic reduction in the calcination temperatures for the introduction of Europium into Stannate structures.There were observable changes in the morphology of all the three Stannates even though the percentage of Europium was less than one.The Cubic structure of Europium doped barium stannate was achieved at a lower calcination temperature of 1000°C contrary to the reported temperature of 1400°C by solid state mixing.There was a progressive decrease in the photo luminescence intensity of the Stannates of Ca with increasing doping percentage of Europium which were correlative of the influence of defect structures in the crystal lattice.It can also be concluded that photocatalytic efficiency of Europium doped calcium and barium stannate upon degradation of methylene blue dye are not noteworthy under the given experimental conditions and further studies on various reaction conditions are needed.The anti-microbial activity is encouraging as indicated by their toxicity on Pseudomonas aeruginosa,Staphylococcus aureusbacteria.The study ultimately provided a novel method of doping of the rare earth metal into the crystal lattice of Calcium and Barium stannate ceramic to widen its applications.

acknowledgement
The authors would like to thank Ethiraj College for Women, Chennai, India for their support and encouragement,

photo Catalytic degradation of Methylene Blue dye-preliminary Screening
was subjected to sunlight radiation.The uV-Visible absorbance of the samples were recorded at the time interval of every 1 hour starting at the zeroth time.The photo catalytic degradative efficiency of the samples was calculated by using the formula.

X-ray -diffraction analysis pXrd Spectrum of Eu 3+ doped nanoscale Calcium Stannate Ceramic
The X-ray diffraction (XRD) pattern of the as synthesized Eu 3+ doped CaSnO 3 (Figure-1, 2 and 3) shows the position of various diffraction peaks at 2θ values and has good agreement with the diffraction pattern of calcium stannate in orthorhombic phase [JCPDS 77-1797] and few residual peaks with low intensity conforming to the SnO 2 in tetragonal phases [JCPDS 88-0287].It was found that the average crystallite size of SnO 2 phases increased with increasing weight percentage of Europium.The number of SnO 2 phases decreased with increasing weight percentage of Europium.Y.Karabulut et al., 10 reported the average crystallite size of Europium doped calcium stannate around >30 micrometer at calcinations temperature 1400°C.

application Studies photoluminescence Study photoluminescence Spectrum of Eu 3+ doped nanoscale Calcium Stannate Ceramic The
Table-1.The EDAX results indicate the progressive addition of the Eu 3+ ion into the crystal lattice but the crystal structures of the basic Stannates decide the exact location of the ion.In both the stannates, the relative percentage of Europium at the surface was when the weight percentage of it was 0.75%.
Photoluminescence(Pl) study of the nanoscale Calcium stannate ceramic doped with three