Surfactant-Assisted BaTiO3:Eu3+@SiO2 CoreâShell Superstructures

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Surfactant assisted BaTiO3:Eu3+@SiO2 core-shell superstructures obtained by ultrasonication method: Dormant fingerprints visualization and red component of WLED applications Dhanalakshmi Muniswamy, Hanumanthappa Nagabhushana, R. B. Basavaraj, Giriyapura Prabhukumar Darshan, and Daruka Prasad B ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04870 • Publication Date (Web): 20 Feb 2018 Downloaded from http://pubs.acs.org on February 20, 2018

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ACS Sustainable Chemistry & Engineering

Surfactant assisted BaTiO3:Eu3+@SiO2 core-shell superstructures obtained by ultrasonication method: Dormant fingerprints visualization and red component of WLED applications Dhanalakshmi Muniswamy 1, 2, Hanumanthappa Nagabhushana3, #, R.B. Basavaraj3, Giriyapura Prabhukumar Darshan4, Daruka Prasad B5, ¥ 1

Department of Physics, Government Science College, Nrupatunga Road, Bengaluru-560 001, India 2

Research and Development Center, Bharathiar University, Coimbatore 641046, India 3

Prof. C.N.R. Rao Centre for Advanced Materials, Tumkur University, Tumakuru-572103, India

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Department of Physics, Acharya Institute of Graduate Studies, Soladevanahalli, Bangalore 560 107, India

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Department of Physics, BMS Institute of Technology and Management, Avalahalli,

Doddaballapur-Yelahanka Road, VTU, Belagavi-affiliated, Bangalore 560 064, India * Corresponding authors: # [email protected] (H. Nagabhushana) and ¥ [email protected] (B. Daruka Prasad)

Abstract Nanoparticles (NPs) synthesized via glib sonochemical route showed excellent assembly of BaTiO3:Eu3+@SiO2 superstructures (SS) using CTAB as a surfactant. Crystallite size, phase, surface science and core-shell confirmation were done through advanced characterization techniques. Experimental parameters like pH, temperature, surfactant concentration were varied and obtained SS with high surface modifications and reported the possible mechanisms for the same. SEM images revealed the broom-like structures and various experimental parameters to dissolve them into freestanding sticks was discussed. CIE chromaticity coordinates were in the range of orange-red region to pure red region. Drawbacks associated with the commercial powder dusting method for visualizing the dormant fingerprint (DFP) viz., high background scattering and high auto-fluorescence of the substrate material was improved with the help of the prepared SS as a dusting powder. Visualization of DFPs and sweat pores on various kinds of surfaces was studied effectively, systematically and revealed the well-defined first, second and third-level ridge particulars with high contrast, high selectivity and low background interference. These results suggest different strategies to engineer SS and highlights to obtain high resolution DFPs. Prepared compounds are also utilized for their use in anti-forging ink and optoelectronics applications.

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Keywords: Sweat pores; Oriented Attachment; Security ink; Powder dusting method; Ultrasonication. Introduction

Encapsulation of one kind of nanoparticles (NPs) with other kind of NPs leads to the formation of core-shell structure which modulates the materials properties. Modulation of properties helps to obtain advanced applications in the field of high frequency electronics, ferroelectric and spintronics, photonics and catalysis [1-4]. Silica coated superstructures (SS) has been studied extensively during the past decade with significant progress because of their special properties, biocompatible nature and finds applications in medical field. [5-7]. If the silica nanospheres were covered with the layers of phosphor materials which leads to increased packing density and also an excellent visible light scattering anisotropy when compared to the conventional commercial phosphor materials [8, 9]. When silica was used as a core and BaTiO3:Eu3+ as shell makes this material further more special when compared to bare BaTiO3:Eu3+ phosphor. This is because both silica and BaTiO3 NPs of core-shell structure show high chemical stability, excellent optical transparency and controllable shells thickness. [10-12]. Piezoelectric nature of BaTiO3 could positively influence enhanced cellular activity. Ball et al., showed that the toxicity of BaTiO3 porous structures confirms the long term cytotoxicity of about 7.4 % even after 72 h when cultured mouse osteoblast cell line using BaTiO3 NPs. [13].

It has the distinct potential in tissue engineering where

mechanical activation can be achieved using ultrasounds and it is useful for cellular proliferation and activity. [14, 15, 16] BaTiO3 P(VDF-TrFE) membrane showed favoraing adhesion, spreading, proliferation makes these compounds as advantageous alternative for guided tissue regeneration (GTR) [17]. Santhosh et al., in their review article expressed that the core-shell and hybrid core-shell nanostructures of SiO2 with various metal and polymers are less toxic in nature. These properties are playing key role in the design of the medical devices, especially in drug delivery, tissue engineering, plastic surgery etc. [18]. 2


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For the preparation of the core-shell structures, inverse micelle, double-jet precipitation, template directed self-assembly, encapsulation of silica NPs by the in-situ polymerization, bioengineering and bio-template techniques are few of the techniques used [19-25]. Yuan et al. prepared BaTiO3/BaTiO3@SiO2 ceramics with layered structure by tapecasting and lamination methods. They reported that by adding additional SiO2 layer, the electric field redistribution and the interface blocking effect increased the dielectric breakdown strength. [26] Liu et al. prepared BaTiO3@Al2O3 nanofibers using solution casting method. They tuned the effective solution for enhancing the discharged energy density of nanofibers. [27] Wang et al., prepared BaTiO3:SiO2 core-shell nanofibers by solution casting method.

In their report they mentioned that polyimide BaTiO3:SiO2

nanofibers showed 200 % greater energy density as compared to best commercial polymer. [28]. Most of the conventional methods are high temperature solid state reactions because in low temperature solution-based synthesis methods toxic organic reagents were generally used. To make low temperature solution based synthesis as biocompatible and less toxic; bio-templates approach became popular. One example is the use of bioengineered viruses for the synthesis of inorganic materials. With this it is able to obtain 1D – nanowires, 2Dnanofilms and also 3D scaffolds. To synthesize BaTiO3, a complex metal oxide at low temperature by biotemplate approach requires biomineralization of proteins extracted or adopted from biological systems, templating macromolecules, catalyzing nucleation and vectorial regulation of growth. Li et al. used genetically engineered M13 bacteriophage filamentous virus for the synthesis of tetragonal phase BaTiO3. [29] Teyeb et al., scaled up the preparation of BaTiO3 NPs using low-temperature bioinspired principles. In their report they used the techniques of enzyme-mediated biosilicification where they developed synthetic analogs to enzyme and translated this through kinetically controlled catalytic 3



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hydrolysis and polycondensation without the use of biochemicals. [30] In biological approaches, the challenges are the maintenance of phase-pure stoichiometric ratios of Ba:Ti, accurate control over grain size at nanoscale, selective crystallization between tetragonal (ferroelectric) over the cubic (paraelectric) phases and difficult to scaled-up to produce large quantity[31]. Self-assembly of NPs to obtain significant surface chemistry is important and can be achieved by organic-NPs based SS such as organometallics’, polymers, artificial DNA etc., [32, 33]. However, inorganic-NPs based SS could also be important for a broad range of applications viz., catalysts, thermoelectric materials, battery electrodes, magnetic materials, fuel cells, solar cells, high temperature additives for propellants, explosives and pyrotechnic, forensic applications, master nanocomposite and structural components [34-37]. So, among the various methods of preparations, ultrasound assisted sonochemical route has many advantages viz., decreased reaction time, mild reaction conditions, resourcefulness of used solvents and prevention of toxic chemicals.

In this method, the cavitational

disintegration at a very high temperature and pressure results in self-assembly of NPs to form SS [38-42]. Hence this method was adopted to prepare BaTiO3:SiO2 core-shell assemblies. In forensic labs, to visualize and analyze the fingerprints (FPs) of the criminal, it is very difficult to see the dormant fingerprints (DFPs) effectively. Several techniques viz., powder dusting, cyanoacrylate fuming, ninhydrin and small particle reagent methods were utilized for this purpose [43, 44]. To overcome from the drawbacks associated with powder dusting technique such as low sensitivity, low contrast, high background noise, and high autofluorescence interference [45], luminescence labeling powders are considered to be the most efficient and significant agents [46,47]. Regular powder dusting often requires additional spraying of a luminescent stain for better LFP visualization [48]. Powder dusting using small particles reagents ends with weak developments of LFPs with quick time decay [49, 50]. These labeling powders exhibit several benefits namely exceptional photo- chemical

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stability, enhanced luminescence property, morphological variations and low toxic nature. Further, drawbacks of associated with anticounterfeiting applications were also to be addressed with new techniques [51, 52]. In the present work, ultrasound assisted sonochemical route using CTAB as a surfactant was used to engineer 3D BaTiO3:Eu3+@SiO2 SS. The assessment processes to demonstrate the growth mechanism of BaTiO3:Eu3+ (5 mol %) NPs to form a 3D SS relating nucleation/growth, aggregation mechanisms and self-assembly of NPs was interpreted. Selected compositions were explored as a labeling agent for the visualization of DFPs on various porous and non-porous surfaces.

Further based on their optical properties and

dielectric properties, it was concluded that the prepared materials are promising materials for optoelectronic devices. Experimental Synthesis of BaTiO3:Eu3+@SiO2 (1-11 mol %) SS For the preparation of BaTiO3:Eu3+ (1-11 mol %) SS, stoichiometric quantity of analytical grade, Barium nitrate [Ba(NO3)2, (Sigma Aldrich 99.9%)], Titanium (IV) Isopropoxide [Ti[OCH(CH3)2]4, (Sigma Aldrich 97 %] and Europium nitrate [Eu (NO3)3, (Sigma Aldrich, 99.9 %)] were dissolved in 100 ml double distilled water and mixed thoroughly using magnetic stirrer. To this mixture, different concentration of CTAB (Cetrimonium bromide) was added to the above resultant reaction mixture. Drop wise NaOH solution of 0.1 M was added to adjust the various pH (5, 6, 7, 8, 9 and 10) values. A titanium horn probe sonicator with ultrasonic frequency ~ 20 kHz and power ~ 300 W was subjected to the reaction mixture for sonication time of 1 - 6 h. The precipitate obtained at the end of the reaction was filtered and washed several times using double distilled water and alcohol. The obtained powder was dried at 80 C for 3 h in a hot air oven and then heat treated at ~ 700 oC for 3 h.

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Further, Stöber method was used for the synthesis of SiO2:BaTiO3 core-shells as reported elsewhere [53]. The final products were characterized by advanced techniques and photoluminescence studies were carried out. Schematic diagram to demonstrate synthesis of BaTiO3:Eu3+@SiO2 (1-11 mol %) SS was as shown in Fig.1. Visualization of DFPs by using BaTiO3:Eu3+@SiO2 (5 mol %) SS as a dusting powder and preparation procedure for security ink

All the DFPs were collected from single donor by a standard procedure as reported elsewhere [10]. The developed DFPs were recorded by using 50 mm f/2.8 G ED lens Nikon D3100/AFS digital camera under UV 254 nm light. The superiority of visualized FPs on various porous and non-porous surfaces was evaluated by using Bandey scale developed by UK Home Office [52]. According to Bandey system, grade 3 or grade 4 FPs are considered for explicit identification of individuals but which were very difficult to visualize using commercially available dusting powders. To obtain security ink with the most favorable performance, BaTiO3:Eu3+@SiO2 (5 mol %) NPs were added to PVC gold medium. Resulting solution was subjected to stirring and sonication for about 10 min each and was used as a dip pen security ink can be excited under UV 254 nm and photographed for visualization. Characterization techniques Structural properties were analyzed using powder X-ray diffraction (PXRD) data measured by Shimadzu 7000, Cukα (1.541 Å) radiation. Morphology was studied by Hitachi table top (Model TM 3000) for scanning electron microscopy (SEM) analysis and Hitachi H8100 (200 KV), LaB6 filament equipped with Energy dispersive x-ray spectroscopy (EDS) (Kevex sigma TM Quasar, USA) was used for transmission electron microscopy (TEM) analysis and Jobin Yvon Spectroflourimeter Fluorolog-3 operational with 450 W Xenon lamp as an excitation source was used for photoluminescence (PL) measurements. Nikon D3100 digital camera having AF-S Nikon 50 mm f/1.8G ED lens and 254 nm UV light was used for the visualization and to take the photographs of DFPs. 6


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Results and Discussions PXRD profiles of pure, Eu3+ doped and BaTiO3:Eu3+@SiO2 (5 mol %) with different coating (I-IV coat) SS were shown in Fig.S1. The intense and narrow single diffraction peaks confirms the formation of single phase and are in good agreement with the standard JCPDS file for BaTiO3 (JCPDS 74-1961). As BaTiO3:Eu3+ (5 mol %) NPs coating on core SiO2 increases, a small diffraction peak attributed to SiO2 was observed at 2θ = ~ 22.8o. Average crystallite size (D) was estimated by using Scherrer’s relation [53] and the obtained results were given in Table 1. Fig.2 (a) shows the excitation spectrum of Un-coated and SiO2 coated BaTiO3:Eu3+ (5 mol%) NPs recorded at 612 nm emission shows peaks at ~ 393 nm, 462 nm and 526 nm were attributed to 7F0 5L6, 7F0 5D2 and 7F0 5D1 transitions of Eu3+ ions respectively [54]. The excitation intensity of SiO2 coated BaTiO3:Eu3+ (5 mol %) NP is higher than that of the un-coated system, which is due to the extent of reduction of surface effect in core-shell. However, this was not happen in this study. This can be explained on basis of amount of Eu 3+ ions in Ba2+ sites. Room temperature (RT) emission spectra of BaTiO3:Eu3+ SS excited under 462 nm was shown in Fig. 2 (b) which shows a series of characteristic Eu3+ emission peaks at ~ 585 nm, 620 nm, 650 nm and 705 nm were ascribed to 5D07F1, 5D07F2, 5D07F3 and 5D07F4 4f6 transitions respectively.

PL intensity was found to be increased up to 5 mol % and

subsequently diminishes due to concentration quenching phenomena [55, 56]. In order to study the effect of various layers of coating (from I to IV) on PL intensity, the compound was excited at λexc of 462 nm and reported its emission spectra (Fig.2 (c)). PL intensity was

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increased up to III coat and afterwards diminishes (Fig. 2 (d)) can be anticipated based on the increased concentration of Eu3+ ions with the increase of number of coating and after third coat, the decrease in trend was due to quenching phenomena. CIE (Commission Internationale de I’Eclairage) chromaticity coordinates and CCT (Correlate Color Temperature) of prepared SS were estimated (Figs.2 (e & f)) and the corresponding values were tabulated in Table 1.

It was found that the CIE chromaticity

coordinates (x, y) were varied from orange–red (0.488, 0.295) to pure red region (0.653, 0.339) [57]. However, the average CCT value was found to be ~ 2173 K which is less than the value of standard illuminant for warm white light (5000 K). Further, quantum efficiency (QE) of the prepared NPs was estimated by the following relation [58]:

QE 

Number of photons emitted E  Ea  c Number of photons absorbed La  Lc

--------- (1)

where, EC ; the integrated luminescence of the phosphor caused by direct excitation, Ea ; the integrated luminescence from the empty integrating sphere, La; the integrated excitation profile from the empty integrating sphere, Lc; the integrated excitation profile when the sample is directly excited by the incident beam. The estimated QE is given in Table 1. As can be evident from the table, the highest QE was obtained to be ~ 77 % for BaTiO3:Eu3+ @ SiO2 NPs. These photometric results evident that prepared optimized compound can be used as an efficient phosphor for optoelectronic devices and their related applications. Lifetime decay curves of uncoated BaTiO3:Eu3+ (5 mol %) and SiO2 coated BaTiO3:Eu3+ (5 mol %) phosphors were estimated as shown in Fig.3. It was noticed from the decay plot that the decay profiles of both the samples have same trend, which is due to the unaltered structure of BaTiO3:Eu3+ (5 mol %) after several coatings. To understand luminescence decay performance the decay data was fitted with different decay relations. It was found that curves follow bi and tri exponential decays given by the relations: 8


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I (t )  I 1e



1

 I 2e

1



1

2

------------- (2)

where I1 and I2 ; the intensities at different times and their corresponding lifetimes τ1 and τ2. The average lifetime for tri-exponential decay can be estimated by using the relation:

 avg 

I 1 1  I 2 2 2

2

I 1 1  I 2 2

I (t )  I 1e



1

1

 I 2e



-------------- (3) 1

2

 I 3e



1

3

------------ (4)

The average lifetime in case of tri-exponential decay can be estimated by using the following equation;

 avg 

I 1 1  I 2 2  I 3 3 I 1 1  I 2 2  I 3 3 2

2

2

------------ (5)

where I1, I2 and I3 are the intensities at different times and their corresponding lifetimes τ1, τ2 and τ3 respectively. From the figure it was noticed that the decay speed was faster in uncoated phosphors to that of coated phosphors [59]. This was mainly ascribed to presence of deeper trap densities in SiO2 coated phosphors compared to uncoated one. Further, SiO2 acts as a protective layer which delays the inter diffusion of oxygen ions into the BaTiO 3:Eu3+ (5 mol %) phosphors consequently decreasing the thermal degradation and improving thermal stability. During the experiment, the prepared BaTiO3:Eu3+ (5 mol %) NPs were collected at various ultrasound irradiation time intervals (1- 6 h) with 25 W/V CTAB concentration and the morphological modifications was performed by scanning electron microscope (SEM) and transmission electron microscopy (TEM) analysis. At the early stage of (1 h) ultrasound irradiation time, the sample showed a cone like structures (Fig.4). As the irradiation time was 9



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increased from 1 h to 2 h, several cones were starts self-assembling side by side. When the irradiation time was increased to 3 h and 4 h, hexagonal cone shaped morphology was found. When ultrasound irradiation time was prolonged to 5 h and 6 h, tip of the cones gets sharpened to form long needle-like shaped structure was observed (Fig.4). In all these types of morphology, nature preferred to utilize the least possible energy in bringing and bonding all the core-shell structures.

Theoretical and further experimental supports for this are

necessary to explore in near future. The primary morphological study of the prepared 3D BaTiO3:Eu3+ (5 mol %) NPs for various ultrasound irradiation times were investigated, which evident that the irradiation time has a considerable effect on the morphology of prepared three dimensional (3D) SS. The whole assessment processes to demonstrate the growth mechanism of BaTiO3:Eu3+ (5 mol %) NPs to form a 3D-SS relating nucleation/growth, aggregation mechanisms and self-assembly of NPs was analyzed studied. Fig.4 (b) shows the schematic representation of formation of cone-like morphology of the prepared sample. Various self-assembled SS were investigated by using surfactant with an appropriate concentration. In the present work, CTAB as a was used as a surfactant to achieve diverse BaTiO3:Eu3+ (5 mol %) SS. Fig.5 shows the impact of different CTAB concentrations (5 W/V to 30 W/V) on morphology was investigated while by maintaining 3 h ultrasound irradiation time. Initially, the CTAB concentration was maintained to ~ 5 W/V and 10 W/V, primary particles undergo elongated growth in an oriented direction (Fig.5 (a & b)). When the concentration of CTAB was increased to 15 W/V and 20 W/V, oriented growth particles undergo Ostwald’s ripening to form broom stick like structures (Fig.5 (c & d)). However, further increase of CTAB concentration to ~ 25 W/V and 30 W/V sharp tipped broom stick like morphologies were observed (Fig.5 (e & f)). Formation of these SSs involves various growth stages viz., nucleation, selfassembly, oriented striking, aggregation followed by Ostwald ripening, oriented attachments 10


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and growth. Growth mechanism can be observed where selective adsorption of surfactant molecules by smaller particles and reassembling of them to adhere collectively without deviating from crystallographic configurations. In the present work, CTAB was chemically adsorbed onto the surface of NPs and kinetically controls the growth rates of various faces by interacting with the faces through adsorption and desorption [60]. The schematic representation to show role of CTAB surfactant in forming broom-like SS was illustrated in Fig.6. In the presence of CTAB, the precursors were nucleated and grown into unstable small-sized nanorods (Fig.6, STEP: 2). CTAB drives these preformed nanorods to assemble and to form longer nanorods in an orderly oriented direction. Moreover, the formed junction in the broom-like structure is normally due to rapid crystal growth. At a successive stage, smooth surfaced self-assembled nanorods were attributed to fact of dissolution and recrystallization processes. Fig. 7(a-f) shows the SEM images of BaTiO3:Eu3+ (5 mol %) NPs synthesized by varying pH level during experiment by maintaining 3 h of ultrasound irradiation time. In the beginning, small sized nano rods were observed accomplished to form broom-like structures (at pH = 5). As pH level of solution was increased gradually from 6 to 10, step by step selfassembly of small sized nano rods to form broom like structures was observed. Fig. 7 (g) illustrates the formation mechanism of broom - like structures via pH-induced transformation. Based on the reaction kinetics and reactants concentrations, the growth mechanism for the formation of broom-like structures includes two steps; (i) nucleation, and (ii) their growth and ordered oriented attachment. The nucleation stage was mainly depends on the surrounding conditions, namely, nature of the reactants (either acidic or basic), concentration of metal ions, and hydrogen ion concentration, i.e., pH level etc. Depends on these experimental conditions, nuclei formation occur rapidly which further undergo growth and self-assembly to form nano/microstructures. In our present case, nucleation begins at low pH value = 5 which 11



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favor the formation of nucleation to form small shaped nano rods, which further grow and self-assembled to form broom-like structures as pH value of solution increases. Additional details of SEM analysis where the comparison of ultrasoncation morphological results with mechanical stirring methods and also the enlarged portion of broom like structures were presented in supplementary section as Fig. S2 and S3. Fig.S4 shows the TEM, HRTEM and SAED patterns of BaTiO3: Eu3+ (5 mol %) and various coated (I-IV) BaTiO3:Eu3+@SiO2 (5 mol %) NPs. Spherical uniform silica core has been coated by thin shell of BaTiO3:Eu3+ (5 mol %) NPs with a thickness of ~ 10–12 nm was observed in Fig. S4. The estimated interplanar distance (d) for prepared samples for (111) and (113) planes was found to be ~ 0.30 and 0.32 nm respectively (Inset of Fig.S4). The measured value of ‘d’ was consistent with the ‘D’ estimated from Scherrer’s relation. Major chemical constituents of finger prints (FPs) originating from epidermis, the secretory glands (including three sweat types), intrinsic and extrinsic contaminants such as metabolites, drugs, blood, grease, food contaminants, moisturizers, hair care products and etc. The important contributing sources of natural materials found on the finger tips were apocrine, eccrine, keratinizing epidermis and sebaceous [61]. Even though, these FPs sources certainly contribute to FP residue but they do not give either a comprehensive list or acknowledge probable chemical activity over the time between deposition and visualization. During visualization of DFPs, the substrate on which FPs was deposited was very significant were broadly classified into two types: porous and non – porous substrates [62]. In the present work, BaTiO3:Eu3+@SiO2 (5 mol %) NPs were used to visualize high resolution DFPs on various porous and non-porous surfaces. Fig.8 shows the DFPs visualized by staining optimized BaTiO3:Eu3+@SiO2 (5 mol %) NPs on various non-porous surfaces including aluminum foil, mobile screen, glass bottle, metal scale, wooden block and stainless steel under normal and UV 254 nm light by powder dusting method. Usually, FP residue is 12


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usually absorbed into porous surfaces but remains on the surface of non-porous surfaces. The visualized DFPs exhibits clear ridge microstructures with good sensitivity and selectivity due to small particle size and better adherence property of the reagent [63, 64]. This demonstrated the practicability of prepared NPs for visualize DFPs on non-porous surfaces. Generally FPs patterns were categorized into three different levels. Level 1 pattern exhibits delta, loop and whorl which were not distinct for recognition. However, in Level 2 details refer to minutiae ridge details namely bifurcation, cross over, lake, hook, short ridge, island and etc which were clearly distinctive patterns. In level 3 types were well-defined ridges containing sweat pores, ridge path deviations and edge contours, which were considered as extremely vital quantitative data to identify individuals. In the present study the level 2 and level 3 fingerprints were studied in detail. Close inspection of fingertips reveals that they contain permanent, immutable and unique pores that are distributed on the ridges. The possible use of sweat pore for identification of individuals was first attempted [65] in studies that show that 20–40 pores are most sufficient to create patterns that are required for a human’s identity. DFPs by staining with optimized BaTiO3:Eu3+@SiO2 (5 mol %) NPs under normal and UV 254 nm light on glass surface exhibits level 3 ridge patterns (more than 40 pores), level 1 and level 2 (bifurcation, eye, delta, enclosure, bridge, ridge ending, and crossover) details was shown in Fig.9. These sweat pores are more distinctly observed under normal light as compared to UV 254 nm light. The results evident that the all the FP details from levels I to III are detected and validated their possibility in forensic analysis. Fig.S5 shows the DFPs of different donors on aluminum foil surface visualized by staining optimized BaTiO3:Eu3+@SiO2 (5 mol %) NPs under normal light and UV 254 nm light. The different ridge details namely central whorl, ulnar arch, plain arch and pocket whorl of all the four donors were clearly observed. The above results clearly exhibits that use

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of optimized BaTiO3:Eu3+@SiO2 (5 mol %) NPs for DFPs visualization can reveal added ridge details, leading to the high sensitivity of the visualization method. To demonstrate the background hindrance of the BaTiO3:Eu3+@SiO2 (5 mol %) NPs based visualization; various textured marbles were selected as a surface, where DFPs were printed, stained by optimized NPs, and then visualized by normal and UV 254 nm light (Fig.S6). Well defined ridge microstructures could be clearly observed without background hindrance or color disruption after light illumination, leading to exceptional contrast for visualized FP development.

Further, we continued with the assessment of optimized

BaTiO3:Eu3+@SiO2 (5 mol %) NPs for visualization of DFPs on the porous surfaces namely magazine covers with different backgrounds as shown Fig.S7. To authenticate the use of prepared BaTiO3:Eu3+@SiO2 (5 mol %) NPs to visualize DFPs on glass surface under UV 254 nm light by maintaining different temperatures was shown in Fig.S8. This study was taken into consideration for checking the effect of temperature and humidity on the quality of ridge patterns in fingerprints [66]. A well-defined clearer ridge pattern was observed at room temperature i.e. 27 oC while unclear FP pattern was identified as the temperature was raised to 47 oC due to rate of loss of water in case of higher temperature. Findings indicate high temperature results in increased degradation of amino acids compared to aging at room temperature. The above combined results indicate that the prepared optimized BaTiO3:Eu3+@SiO2 (5 mol %) NPs can be used effectively in forensic analysis at different environmental conditions. The chemical constituent of DFPs is greatly variable, as major changes take place after deposition through surface interactions and various decomposition and oxidative mechanisms. FPs composition can be separated into two parts: (i) the initial composition, at deposition where compounds within the digit residue are transferred to the substrate in the deposition stage and (ii) the aged composition, containing the remaining initial compounds

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and the degradation products following the aging stage. A little research has been explored to identify the changes between the initial and aged compositions and the rate of change with time. Therefore, to demonstrate the practicability of the fabricated BaTiO3:Eu3+@SiO2 (5 mol %) NPs for visualization of DFPs, we conducted series of experiments after FPs had been aged up to 45 days. The detection sensitivity gradually decreased with increasing aging of the FPs, due to the gradual evaporation of the FP compositions (Fig. 10). However, DFPs aged for up to 3 weeks could be clearly visualized with high sensitivity. DFPs developed and their ridge characteristics developed by traditional powders, including commercial powders were compared with the prepared compounds (Fig. S9). It can be seen from the figure that the prepared compounds shows the better ridge patterns up to level 4.

Hence prepared

compounds were better than the commercial and regularly used dusting powders. Use of SS for the DFPs was better than the other reported literature in terms of size of the particle, less agglomeration of NPs in SS helps of better adhesion the surface, level of DFPs observed and also the decay time [67-69]. In these studies, laser light was used for excitation but in our work the excitation is with UV light of 254 nm. Further, in all the various backgrounds it is possible to identify and study up to level 3 ridge patterns easily. In recent years, many anti-counterfeiting technologies such as simple marker, plasmonic security labels, holograms and security inks, etc. were explored as a protection against counterfeiting [70, 71]. However, from security point of view, the luminescent materials provide advanced security due to their unique physical, chemical and optical properties. Although, there are many semiconductor NPs namely CdS, CdSe, CdTe etc. were used as luminescent security ink but they have their own demerits like toxicity, broad emission and solubility in harmful solvent [72-74]. The formation of stable and transparent solution of these NPs is also a complex task. Moreover, the lanthanide doped phosphors have many advantages over these materials like low toxicity, sharp emission and good solubility.

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Hence, the lanthanide based transparent security ink has become a beneficial tool for security labels, identification markers, barcode system etc. Keeping all the advantages of lanthanide based transparent security ink, we explored anti-counterfeit tags of BaTiO3:Eu3+@SiO2 (5 mol %) NPs ink painted by dip pen mode under normal and UV 254 nm light. In Fig.11 (A1−E1 & A2−E2) are shown digital photographs of letters handwritten using an anti-counterfeiting ink prepared by incorporating BaTiO3:Eu3+@SiO2 (5 mol %) NPs ink into a PVC gold media. Upon UV 254 nm light irradiation, the BaTiO3:Eu3+@SiO2 (5 mol %) was found to display strong red emission with a high quantum efficiency. Similar type of work has been studied by Sun et al. introduced an approach to fabricate anti-counterfeiting inks based on photoluminescent lanthanum-doped ZnO QDs, synthesized by a modified sol–gel method [75-77].

Conclusions

Glib strategy was employed to obtain the BaTiO3:Eu3+@SiO2 core-shell SS by ultrasound assisted sonochemical route using CTAB as a surfactant. Growth mechanism of superstructures with broom like architectures were obtained by controlling influential parameters such as CTAB concentration, pH of reactants, frequency of ultrasound waves and the conditions were set in in favour of nucleation and growth of crystals led to core-shell entities. By varying experimental parameters, the junction in the broom-like structures was dissolved and the freestanding broom-sticks were generated. The PL emission spectra displays a peak at 585 nm, 620 nm, 650 nm and 705 nm were attributed to the transitions 5

D07F1, 5D07F2, 5D07F3 and 5D07F4 of Eu3+ ions respectively. The CIE chromaticity

coordinates were varied from orange-red region to pure red region (0.653, 0.339) by changing experimental parameters. DFPs visualized by BaTiO3:Eu3+@SiO2 (5 mol %) NPs exhibits high efficiency and high sensitivity when compared to commercially available toxic dusting

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powders also its fading studies showed that up to 45 days the helps in forensic and antiforging applications. Aforementioned results evident that prepared optimized compounds can also be used as an efficient phosphor for optoelectronic devices.

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nanoparticles in a dry powder state, Nano Res. 2015, 8, 1800–1810. https://dx.doi.org/10.1007/s12274-014-0686-6 P. D. Barnett, R. A. Berger, The effects of temperature and humidity on the permanency of latent fingerprints, Science and Justice, 1976, 16, 249-254. https://doi.org/10.1016/S0015-7368(76)71068-5 P. Thakur, R. K. Garg, New Developing reagent for latent fingermark visualization:Fuller’s earth (Multani Mitti), Egypt J Forensic Sci , 2016, 6, 449-458. https://doi.org/10.1016/j.ejfs.2016.11.007 Y. Qiao, C. Cappelle, Y. Ruichek, Visual localization across seasons using sequence matching based on multi-feature combination, Sensors, 2017, 17, 2442 (22 pp). https://dx.doi.org/ 10.3390/s17112442 C. Suresh, H. Nagabhushana, G.P. Darshan, R.B. Basavaraj, B. Daruka Prasad, S.C. Sharma, M.K. Sateesh, J.P. Shabaaz Begum, Lanthanum oxyfluoride nanostructures prepared by modified sonochemical method and their use in the fields of optoelectronics and biotechnology, Arab. J. Chem., https://doi.org/10.1016/j.arabjc.2017.03.006. Y. Cui, R. S. Hegde, I. Y. Phang, H. K. Lee, X. Y. Ling, Encoding molecular information in plasmonic nanostructures for anti-counterfeiting applications, Nanoscale,2014, 6, 282-288. https://dx.doi.org/ 10.1039/C3NR04375D K. Huang, J. M. Carulli, Y. Makris, Counterfeit electronics: A rising threat in the semiconductor manufacturing industry, Int .Conf. IEEE, 2013. 45. https://dx.doi.org/ 10.1109/TEST.2013.6651880 A. K. Deisingh, Pharmaceutical counterfeiting, Analyst, 2005, 130, 271-279. https://dx.doi.org/ 10.1039/B407759H A. Mills, Oxygen indicators and intelligent inks for packaging food, Chem. Soc. Rev. 2005, 34, 1003-1011. https://dx.doi.org/ 10.1039/B503997P R. Abargues, P. J. Rodriguez-Canto, S. Albert, I. Suarezb, P. Mart´ınez-Pastor, Plasmonic optical sensors printed from Ag-PVA nanoinks, J. Mater. Chem. C, 2014, 2, 908-915. https://dx.doi.org/ 10.1039/C3TC31914H Chunyang Li, Xiaodi Du, Dan Yue, Mengnan Wang, Jingbin Huang, Zhenling Wang, Color changing from white to red emission for ZnWO4:Eu3+ nanophosphors at different temperature, Mater. Lett., 2016, 171, 27-29. https://doi.org/10.1016/j.matlet.2016.02.045 F. Grillo, H.V. Bui, J.A. Moulijn, M.T. Kreutzer, J. Ruud van Ommen, Understanding and Controlling the Aggregative Growth of Platinum Nanoparticles in Atomic Layer Deposition: An Avenue to Size Selection, J. Phys. Chem. Lett., 2017, 8, 975–983. https://dx.doi.org/ 10.1021/acs.jpclett.6b02978 L.W. Sun, H.Q. Shi, W.N. Li, H.M. Xiao, S.Y. Fu, X.Z. Cao, Z.X. Li, Lanthanum doped ZnO quantum dots with greatly enhanced fluorescent quantum yield, J. Mater. Chem., 2012, 22, 8221-8227. https://dx.doi.org/ 10.1039/C2JM00040G

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Page 24 of 37

Table.1. Photometric characteristics, average crystallite size (D) estimated by Scherrer’s method and quantum efficiency in BaTiO3:Eu3+ (5 mol %) and BaTiO3:Eu3+@ SiO2 (5 mol %) (I-IV coat) SS. Fluorescent labels

CIE

0.5279

0.4514

2262

Crystallite size (D) in nm 35

BaTiO3:Eu @ SiO2 (5 mol %) (I coat)

0.5371

0.4397

2118

37

68

BaTiO3:Eu3+@ SiO2 (5 mol %) (II

0.5406

0.4305

2040

40

68

0.5462

0.4311

2007

31

77

0.5839

0.3673

35

72

X BaTiO3:Eu3+ (5 mol %) 3+

CCT (K)

Y

QE (%)

65

coat) BaTiO3:Eu3+@ SiO2 (5 mol %) (III coat) BaTiO3:Eu3+@ SiO2 (5 mol %) (IV

1804

coat)

24


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Fig.1. Step 1: Illustration of the formation mechanism of SiO2 cores by Stöber method, Step 2: Demonstrates the synthesis procedure of BaTiO3:Eu3+ SS by ultrasonication route and Step 3: Depicts fabrication of BaTiO3:Eu3+ (5 mol %) @ SiO2 NPs.

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Fig.2 (a) Excitation spectrum, emission spectra of (b) BaTiO3:Eu3+ (1-11 mol %) SS, (c) BaTiO3:Eu3+ (5 mol %) @ SiO2 with coatings (I-IV), (d) PL intensity v/s Eu3+ concentration and SiO2 coatings and (e & f) depicts the CIE and CCT diagrams of BaTiO3:Eu3+ (1 – 11 mol %) and SiO2 @ BaTiO3:Eu3+ (5 mol %) NP.

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Fig.3 Decay curves of (1) BaTiO3:Eu3+ (5 mol %) and (2) BaTiO3:Eu3+ (5 mol %) @ SiO2 (coat IV) SS.

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(a) 1h 10 μm

2h

Ultrasonication process

10 μm

3h 10 μm

CTAB surfactant Barium Nitrate

BaTiO3: Eu3+

4h 10 μm

Titanium Isopropoxide Europium Nitrate

5h 10 μm

6h 10 μm

(b)

Nucleation

Barium Nitrate

Growth

Titanium Isopropoxide

Europium Nitrate CTAB surfactant

Superstructures

Self- assembly

Fig.4 (a) SEM images of BaTiO3: Eu3+ (5 mol %) NP synthesized with different ultrasound irradiation times (1 h, 2 h, 3 h, 4 h, 5h and 6 h) with 25 W/V of CTAB and (b) Schematic representation of formation process of cone-like morphologies.

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(a)

(b)

(c)

10 µm

10 µm

10 µm

(d)

(e)

(f)

10 µm

10 µm

10 µm

Fig.5. SEM images of BaTiO3: Eu3+ (5 mol %) NP synthesized with different concentration of CTAB (a) 5 W/V, (b) 10 W/V, (c) 15 W/V, (d) 20 W/V , (e) 25 W/V, and (f) 30 W/V with 3 h of ultrasonic irradiation time.

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Fig.6. Step 1: Schematic to show role of CTAB surfactant to form broom-like SS and Step 2: Represent the growth mechanism of broom-like SS including nucleation, self assembly and Ostwald ripening process.

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(a)

(b)

(c)

20 µm

20 µm

20 µm

(d)

(e)

(f)

20 µm

20 µm

20 µm

(g) Mixture of Ba2+ + TiO32+ + Eu3+ + CTAB

Clusters

Ultrasound wave Nucleation

Growth of nanoparticles

Self assembly

Broom-like structures

Fig.7. SEM images of BaTiO3: Eu3+ (5 mol %) NPs synthesized with pH values of (a) 5, (b) 6, (c) 7, (d) 8, (e) 9 and (f) 10 with 3 h of ultrasound irradiation time and (g) schematic representation to show formation of broom-like SS.

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Page 32 of 37

5 mm

5 mm

5 mm 5 mm

5 mm

5 mm

5 mm

5 mm

5 mm

5 mm

5 mm

5 mm

5 mm

Fig.8. DFPs visualized by staining optimized BaTiO3:Eu3+ (5 mol %)@SiO2 NP on various non-porous surfaces namely (a, b) aluminum foil, (c) mobile screen, (d, e) glass bottle, (f, g) metal scale, (h, i) wooden block and (j, k) stainless steel under normal and UV 254 nm light.

32


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5 mm

5 mm

Fig.9. Detailed fingerprint ridge characteristics visualized by staining optimized BaTiO3:Eu3+ (5 mol %)@SiO2 NP under normal and UV 254 nm light on glass surface.

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5 mm

5 mm

5 mm

5 mm

5 mm

5 mm

Fig.10. DFPs visualized by optimized BaTiO3:Eu3+ (5 mol %)@SiO2 NP on aluminum foil surface aged for different durations (a) 1 day, (b) 3 days, (c) 1 week, (d) 3 weeks, (e) 1 month and (f) 45 days under UV 254 nm light.

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Fig.11. Anti-counterfeiting labels painted with ultrasonically prepared BaTiO3:Eu3+ (5 mol %) @ SiO2 NP ink under (A1−E1) normal and (A2−E2) UV 254 nm light.

35



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Supporting Information. Brief statement in nonsentence format listing the contents of the material supplied as Supporting Information Supplementary section provides the  PXRD patterns of pure, BaTiO3:Eu3+ and BaTiO3:Eu3+ @ SiO2 (I-IV coat) SS.  Morphology of the BaTiO3:Eu3+ NPs fabricated with different sonication power and also compared them with the NPs prepared by mechanical stirring time.  Reason for broom like morphology is also discussed.  Detailed discussion about the TEM, HRTEM, SAED patterns of BaTiO3:Eu3+ and various coats of SiO2 on BaTiO3 NPs.  Latent finger prints quality on aluminium foil, textured marbles and on magazine covers using BaTiO3:Eu3+ @SiO2 NPs under normal and UV light were discussed.

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BaTiO3:Eu3+@SiO2 core-shell structures were synthesized by simple ultra-sonication method using CTAB as surfactant. Dormant fingerprints were visualized by optimized BaTiO3:Eu3+@SiO2 core-shell superstructures which exhibited high efficiency and high sensitivity compared to other commercially available toxic dusting powders. Further, obtained results are evident for the use of core-shell structure as an efficient phosphor for optoelectronic devices. Growth mechanism of hierarchical broom like architectures was obtained by controlling various influential experimental parameters. PL emission spectra displays a peaks attributed to the transitions 5D07F1, 5D07F2, 5D07F3 and 5D07F4 of Eu3+ ions. CIE chromaticity coordinates were tuned from orange – red region to pure red region using experimental parameters.


Surfactant-Assisted BaTiO3:Eu3+@SiO2 CoreâShell Superstructures

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