Nano Superstructures for

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Facile ultrasound route to prepare micro/nano superstructures for multifunctional applications Hodekallu Jayadevaru Amith Yadav, Bheemaiah Eraiah, Hanumanthappa Nagabhushana, Giriyapura Prabhukumar Darshan, Daruka Prasad Bangari, S. C. Sharma, Halanur Basavarajaiah Premkumar, Kurupalya Shivram Anantharaju, and Giriyapura R. Vijayakumar ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b01693 • Publication Date (Web): 07 Jan 2017 Downloaded from http://pubs.acs.org on January 8, 2017

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ACS Sustainable Chemistry & Engineering

Facile ultrasound route to prepare micro/nano superstructures for multifunctional applications Hodekallu Jayadevaru Amith Yadav1, Bheemaiah Eraiah 1, Hanumanthappa Nagabhushana 2, Giriyapura Prabhukumar Darshan3, Daruka Prasad Bangari 4, S. C. Sharma5, Halanur Basavarajaiah Premkumar6, Kurupalya Shivram Anantharaju7, Giriyapura R. Vijayakumar8 Department of Physics, Bangalore University, Bangalore – 560056, India Prof. C.N.R. Rao Centre for Advanced Materials, Tumkur University, Tumkur - 572 103, India 3 Department of Physics, Acharya Institute of Graduate Studies, Bangalore 560 107, India 4 Department of Physics, B M S Institute of Technology and Management, VTU Affiliated, Bangalore – 560064, India 5 Advisor, Avinashilingam Institute for Home Science and Higher Education for woman University, Coimbatore-641 043, India 6 Department of Physics, Dayananda Sagar Academy of Technology and Management, Bangalore 560082, India 7 Department of Chemistry, Dayananda Sagar College of Engineering, Bangalore 560078, India 8 Department of Chemistry, University College of Science, Tumkur University, Tumkur– 572103, India 1

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* Corresponding author: +91- 9945954010, E-mail: [email protected] and [email protected]

Abstract Dy3+ doped zirconium dioxide (ZrO2) nanophosphors were prepared by cetyltrimethyl ammonium bromide (CTAB) assisted ultrasound method. The PXRD profiles showed pure cubic phase. Morphology changes were observed as as there is a change in sonication time, CTAB concentration, pH and sonication power. The energy band gaps were varied from 4.13 eV to 4.53 eV. PL emission spectra exhibits sharp peaks at ~ 483, 584 and 674 nm were ascribed to the transitions of 4F9/2→6H15/2, 4F9/2→ 6H13/2 and 4F9/2→6H11/2 respectively. The spectroscopic properties of the samples were evaluated by Judd-Ofelt theory. Photometric characterization of prepared samples shows white emission and suitable for light-emitting diodes (LED’s). The optimized ZrO2: Dy3+ (3 mol %) NP was utilized to reveal latent fingerprint on various surfaces. The photocatalytic behavior of ZrO2:Dy3+ NPs was extensively studied by degradation of hazardous methylene blue dye. Overall results confirmed that the method of preparation was significant to achieve white light emitting diodes, UV-lasers, photodegradation and forensic applications.

Keywords: Latent fingerprints; Photoluminescence; Photocatalyst; Solid state lightning; Impedance spectroscopy; Judd-Ofelt analysis.

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Introduction Rare earth ions (RE) doped nanopowders (NPs) exhibit high color rendering index, energy efficient and stable towards radiations hence they have uses in the field of optoelectronics, catalysis and forensic fields [1, 2]. The properties of these materials were mainly dependent on the synthesis routes where structural, morphological and optical properties can be tuned [3].

Due to the tunable hypersensitive transitions of Dy3+ in the yellow and blue regions,

Dy3+ doped materials showed the possibility of obtaining the pure white light emission from single material [4, 5]. Hence, the Dy3+ doped NPs were promising materials for white light generation and possibility to use in various optoelectronic applications [6]. ZrO2 NPs as useful in various applications viz., optoelectronics, fuel-cell technology, gas sensing, coating to protect the optical components etc. which is due to its high melting point, wide band gap, low optical loss and transparent to EM waves of visible and near infrared region [2, 7-10]. ZrO2 exhibits the stable monoclinic phase at room temperate (RT) and transforms into tetragonal at 1443 K and to cubic at 2643 K. At high temperature, tetragonal and cubic phases were unstable in bulk forms. Gu et al. investigated that influence of dopant (Dy3+) and calcination temperature on ZrO2 NPs exhibits enhanced PL property for optimum dopant concentration of 3 mol % [11]. Effect of Dy3+ of 2 mol % in ZrO2 shows prominent PL intensity at 480 nm was reported by Torres et al. [12]. Presently modified ultrasound assisted sonochemical method was used to prepare various micro/nanostructured ZrO2:Dy3+ NPs. In this method of preparation, there is a production of intense heat and high pressure due to the collapse of cavitation bubbles within few nanoseconds which favors the formation of NPs with interesting surface modifications. Fingerprints (FPs) were one of the most important and commonly used forms of physical evidence in forensic investigations [13-14]. Usually, latent FPs which was not having clear visualization at offense sights needs an improvement for imaging and 2


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recognition. Usually powdering method (PM) was used where networked metals of lead, gold and silver were used for the detection of FPs.

Because of toxic chemicals used, this

method requires appropriate ventilation and safety equipment’s. Hence as an alternative for this, the powder based luminescent materials can be used for the effective detection of FPs. In this technique, the surface modification of the NPs has a large influence on the strong bonding efficiency to the FP. In this communication, various concentrations of ZrO2: Dy3+ NPs were prepared by versatile and energy efficient ultrasound route using CTAB as a surfactant.

Dy3+ ions

substitution changes the photoluminescence (PL) properties which open the possibility to use of these compounds in optoelectronic and forensic uses. In addition, diverse self-assembled superstructures (SS) were obtained by tuning the experimental influential factors. The probable formation mechanisms to obtain such structures were also proposed. For the first time we reported on the various hierarchical SS of ZrO2:Dy3+ NPs was reported.

Experimental ZrO2: Dy3+ (1-11 mol %) was prepared by using surfactant assisted ultrasound method. The stoichiometric quantity of zirconyl nitrate and Cetyl trimethylammonium bromide (CTAB) were mixed properly through magnetic stirred a clear solution was obtained. Further, suitable quantity of dysprosium nitrate was added drop-wise to the above solution till the stoichiometry conditions were met. The pH value of the solution was adjusted to desired values (5-11) using 1M of NaOH and 1 M HCl. Then the above solution was stirred using ultrasound sonicator maintained at a frequency of ~20 kHz, temperature of 333 K and the power of ~300 W.

Finally, white precipitate formed was filtered and washed by using

deionized water and ethanol to remove the unwanted traces of ions. The procedure was repeated for different sonication time (1 - 6 h). The final powder was dried at 333 K for 3 h in

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a vacuum oven and used for further studies. Figure.1 shows the schematic diagram for the preparation of ZrO2:Dy3+ NP materials.

Structural properties were obtained by using powder X-ray diffraction (PXRD) data (Shimadzu 7000, Cukα radiation).

Scanning electron microscopy (SEM) images were

obtained by SEM instrument (Hitachi - TM-3000). Transmission electron microscopy (TEM) images were obtained by TEM instrument (Hitachi H-8100 with an accelerating voltage up to 200 KV, LaB6 filament) equipped along with EDS (Kevex sigma TM Quasar, USA). Diffused reflectance spectra (DRS) were obtained by Perkin Elmer (35λ) spectrometer. The photoluminescence (PL) measurement was recorded on a spectroflourimeter (Jobin Yvon Fluorolog-3 equipped with 450W xenon lamp). Nikon D3100 digital camera equipped with an AF-S Nikon 50 mm f/1.8G ED lens and a 254 nm UV light was used for the latent FPs. Raman spectra of the prepared samples were acquired by BRUKER RFS 27: Standalone FTRaman Spectrometer equipped with an Nd: YAG 1064 nm in the spectral range is 4000 – 50 cm-1. The chemical composition was characterized by X-ray photoelectron spectroscopy (Phoibos 150, specs and dual Al/Mg anode X-ray source was used). Cyclic voltammograms (CH instruments 600E model) was used to study the electrochemical impedance spectroscopy of the sample to measure the impedance response of the prepared samples. Results and discussion Figure.2. shows the SEM images of the ZrO2:Dy3+ (3 mol %) NP material in the absence of surfactant CTAB at various sonication times (1- 6 h). The SEM micrograph of ZrO2 obtained at 1 h was advised that the sample exhibits various shapes and sizes of flower shaped particles were shown in Figure.2 (a). The uniform cone shaped structure was obtained when 2 h sonication irradiation. Further increase in sonication time up to 3 h, flower shaped morphology was observed and it is continued even for the reaction time of 4 - 6 h. Hence the time factor during ultrasound treatment greatly influenced the morphologies of the prepared

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materials. The reaction activity usually happens in between the cavitation bubble and the surrounding solution also there is a possibility of reaction inside the collapsing bubbles based on the nature of the powder. In the present case, due to crystalline nature of ZrO2 sonochemical reaction took place in the interfacial region only. The surface interactions were closely associated with the structural properties of ZrO2 and surfactants. Figure.3. shows the effect of different quantity of CTAB (5 - 25 ml) on the morphology was studied with 3 h sonication time. Surfactants with optimum quantity can influence the growth condition for nano/micro SS and were utilized as efficient structure directing agents to prepare NMs with preferred structures. Without the use of surfactant, there were no specific morphology was observed (Figure. 2). But after the addition of surfactant, at lower quantity (5 ml), a flower like growth with various shaped ZrO2: Dy3+ (3 mol %) nanostructures were observed. When the quantity of CTAB was increased to 10 ml and 15 ml, individual flowers attached side by side to form bigger sized particles (Figure. 3). This may be due to the fact that the weaker stabilizing effect of CTAB molecules would be favorable for coalesce of ZrO2 crystalline units. However, with further increase of CTAB quantities to 20 ml and 25 ml, uniform lotus type flower morphology was observed. Hence the amount of surfactant plays a major role to achieve various morphologies of ZrO2 in the sonochemical route. Based on the SEM studies, the pictorial diagrams for development of SS in ZrO2: Dy3+ (3 mol %) compounds (with and without CTAB) was as shown in Figure. 4. By changing the pH value of the solution, growth and shape of the SS could prominently alter. The various morphologies of ZrO2: Dy3+ (3 mol %) material was observed for different pH values (Figure. 3). In the growth stage, to reduce the surface energy, many of the tiny assemblies undergo growth to form various structures.

The unique formation

mechanism was very complex and need further investigation. Figure.5 shows the SEM images of ZrO2: Dy3+ (3 mol %) NPs with different sonication time varied from 1 h to 6 h in

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presence of 20 ml of CTAB surfactant. Numerous factors required to achieve flower like structures to name few, Vander Waals forces, electrostatic, dipolar fields etc. As compared to other synthesis routes, the optimized sonication factors can reduce the crystalline sizes, uniformly distributed particles and reduced synthesis time. Therefore, SS for different sonication power (20 kHz, 22 kHz & 24 kHz) were achieved. Initially, the particles were start opening to form flowerlike structure was observed when the frequency of 20 kHz was applied, (Figure. 6(a)).When increase in the power to 22 kHz & 24 kHz, a flowerlike particles were formed (Figure. 6(b & c)). In absence of ultra-sonication it was evident that the product yield traces of byproducts and their particles shows broader size distributions.

When

mechanical stirring was applied in the place of ultrasound irradiation along with CTAB, the branched structures with small agglomerates (irregular) with micrometer sized particles were observed and were shown in Figure.7. All the samples showed well-crystallized nanoflowers for all the quantities. SEM micrographs, reveals the flower-like structure after stirring over 3 h (Figure. 7). This is because of extended time to complete the precipitation as compared to 1h period of sonication route. This confirms that the sonication route requires less time to synthesis nanostructures and also helps to achieve the formation of better crystallization. The reaction scheme and plausible mechanism for the formation of ZrO2:Dy3+ SS was provided in Figure.8. In the process of formation of ZrO2:Dy3+ reaction mixture containing nitrates of Zr and Dy sources and CTAB were subjected to ultrasonication which in the beginning produces free radicals of H+ and OH- [15]. The free radicals of H2O reacted with nitrates and gave hydroxides of Zr and Dy with the elimination of HNO3. Further hydroxides undergo dehydration at high temperature under sonication to afford micro/nano grains with a white precipitate which is highly insoluble in water, stable and chemically inert. But in the presence of CTAB, the morphology and structural changes occur as represented by schematic

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diagram which shows the plausible mechanism of ZrO2:Dy3+ (Figure.8). CTAB acts as a cationic surfactant which helps for the reorientation of the crystalline particles and micelle formation occurred. These micelle rearrangement and crystallization process occurred during sonication to yield SS (Figure.9). Herein sonication time place an important role to obtain the regularly packed particles compared to without CTAB. TEM, HRTEM images and SAED patterns of ZrO2: Dy3+(3 & 9 mol %) with 1 h sonication time was shown in Figure.9. The TEM images shows thin sheet like nanostructures of ZrO2:Dy3+ material. The HRTEM image shows the clear atomic planes with an average interplanar spacing of ∼0.32 nm and ∼0.28 nm respectively for the 3 & 9 mol % of ZrO2: Dy3+. The SAED patterns were well matched with the (h k l) values corresponding to the prominent peaks of the PXRD profiles which is discussed in the subsequent next section. The PXRD patterns of ZrO2: Dy3+ (1-11 mol %) materials were shown in Figure.10 (a). The observed PXRD profiles were fitted better with the standard JCPDS card No. 49 1642. The spectra of these samples exhibit pure cubic phase without any additional phases [16]. The formation of cubical phase was due to the oxygen vacancies. The tolerable percentage change (Dr) between the radii of doped ion Dy3+ (0.947Ǻ) and Zr4+ (0.89Ǻ) ions was estimated and found to be 6.40% confirms the proper replacement of Zr4+ ions by Dy3+ ions as explained elsewhere [17].

The calculated crystallite size D as per [18] values of

ZrO2: Dy3+ (1-11 mol %) were listed in Table.1. The crystallite size and strain present in the prepared compounds were estimated by Hall-Williamson fitting method [19]. Slope fitted between  cos  /  and sin  /  along y-axis and x-axis respectively gives strain as depicted in Figure.10 (b). The crystalline size and strain were calculated and listed in a Table.1. Further the lattice factors, atomic coordinates were provided with statistical validation through Rietveld refinement using Fullproof software with Pseudo-Voigt function [20]. The refinement result reveals that ZrO2: Dy3+ (3 mol %) sample crystallized in cubic phase and

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space group of Fm ̅ m (225). Figure. 11 (a) shows the best fit curve with the difference and the Bragg’s positions of the sample evaluated with the raw data of PXRD after subtracting the background corrections. The refined structural factors obtained were tabulated in Table 2. The GoF was found to be 0.93 confirms that the prepared sample was in above-mentioned phase. The packing diagram obtained using Diamond Software by providing the necessary structural outputs obtained from Rietveld analysis is as shown in Figure. 11(b). The DRS of ZrO2: Dy3+ (1-11mol %) material was shown in Figure.12 (a). The spectra exhibits sharp peaks at ~ 1073 nm, 1227 nm and 351 nm were due to 6H5/26F9/2, 6

H5/26F7/2 and 6H15/26P7/2 shifts of doped ions [21]. The Kubelka–Munk theory was

employed to estimate optical energy gap (Eg) of prepared ZrO2:Dy3+ (1-11 mol %) materials from DRS. Figure. 12 (b) shows the tangents drawn to the plots of F R  h  versus h 1/ 2

[22]. The estimated values of Eg were calculated and listed in Table.1. Changes in Eg were due to deviated ordered structures in the host matrix and change the energy level distributions [23]. In addition, synthesis routes and conditions can change the type of structural defects which leads to changes in the Eg. Raman spectroscopy is a nondestructive tool for the characterization of defects and to obtain the structural information directly related to the vibrational energies of the molecules. The RT Raman spectra of Dy3+ doped ZrO2 NPs recorded in the range of 200-800 cm-1 is shown in Figure.13. The intense Raman peaks were recorded at 277 cm-1(Eg), 325 cm-1(B1g), 469 cm-1(Eg), 617 cm-1(A1g) and 655 cm-1 (Eg). The observed peak positions matches well with the reported Raman spectra for cubic ZrO2 [24, 25]. Further, these results are in correlation with the PXRD results shown in Figure.10 (a). To know the elementary oxidation states of the ZrO2: Dy3+ (3 mol %) NPs, XPS study were represented as shown in Figure. 14(a-e). The full range spectra were shown in Figure. 14 (a) specifies that all the peaks on the curve were validated to Dy, Zr, O and C elements. 8


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The presence of C at 291.0 eV comes from the carbon adhesive tape used for XPS study (Figure. 14 (e)). Figs. 14 (b - d) display the high resolution spectra corresponds to Zr, O and Dy elements. Zr-3d spectrum (Figure. 14(b)) consists of 3d5/2 at 181.3 eV and 3d3/2 at 184.5eV electronic states. Deconvolution of the spectra produces peaks attributed to the existence of two kinds of Zr4+ species at low and high binding energies pertaining to the different chemical atmosphere. The characteristic spectrum of Zr 3d with Zr at +4 oxidation state confirms the formation of ZrO2 [26, 27]. Further, the investigation for the presence of oxygen vacancies was shown in Figure. 14 (c) for O 1s state, which is unequal in nature, representing the occurrence of multi-component oxygen ions on the surface.

The de-

convoluted curve showed two separate peaks located at 536.5 eV and 532.1 eV can be indexed to O2− and oxygen produced by hydroxyl ions of the surface respectively. These values were very close to those reported in the literature [28]. Figure. 14 (d) shows that the binding energy of Dy 4d at about 161.0 eV which is similar to the reported date in the literature [29]. Figure. 15 (Inset) shows the excitation spectrum of ZrO2: Dy3+ (3 mol %) NPs monitored at emission wavelength of 484 nm. The spectrum exhibit peaks centered at ~ 351 nm, 366 nm, 386 nm and 435 nm were due to 6H15/2→6P17/2, 6H15/2→6P15/2, 6H15/2→4I13/2 and 6

H15/2→4G11/2 transitions of Dy3+ ions respectively [30, 31]. The PL emission spectra of Dy3+

doped ZrO2 excited at 351 nm at RT was shown in Figure.15 exhibits sharp peaks at ~ 483, 584 and 674 nm were attributed to the transitions of 4F9/2→6H15/2, 4

4

F9/2→ 6H13/2 and

F9/2→6H11/2 respectively [32]. The peak at ~ 483 nm and ~ 584 nm were attributed to

electric and magnetic dipole transitions of the Dy3+ ions respectively.

The schematic

representation for the possible energy transitions of ZrO2:Dy3+ NPs was shown in Figure.16. The consequence of increased concentration of Dy3+ on PL intensity was as shown in Figure.17 (a). It was observed that the PL intensity was increased with increase of Dy3+ 9



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concentration up to 3 mol % and later diminishes. The decrease in PL intensity was due to self-concentration quenching phenomena which attributed to energy transfer among dopant ions [33]. The separation between Dy3+ ions was less at higher activator concentration which results in non-radioactive energy transfer between dopant ions. The critical distance (Rc) was estimated and found to be ~ 5.347 Å which was greater than 5 Å leads to the multipole– multipole interaction in the ZrO2 host [34]. To identify the type of multipolar interaction, Dexter and Schulman theory was used. From Figure. 17 (b), the curve of log I/ v/s. log  clearly shows that the slope is ~ -1.415, hence the value of Q was found to be ~ 6.0353 which was close to theoretical value of 6. So, the electric dipole-dipole interaction was the main reason for the concentration quenching in ZrO2: Dy3+ NPs. Asymmetry ratio (A21) was determined as explained elsewhere which confirms that the intensity ratios of various transition of PL profile influences the luminescent property of a material [35]. To study the site symmetry and luminescence behavior of ZrO2:Dy3+ (1-11 mol %) NPs Judd–Ofelt (J-O) factors were evaluated [36, 37]. The three J-O factors, Ωλ (λ = 2, 4 and 6) can categorize the structural background and symmetry of Dy3+ ions in the host matrix. Intensity factors were evaluated by utilizing the PL emission spectra of the prepared materials. The estimated radiative emission changes (A0-J) associated to forced electric dipole according to the procedure explained elsewhere [38]. The estimated values of Ω2 and Ω4 were listed in a Table.3. The factor Ω2 was dependent on the covalence of Dy3+ ions with synchronizing ligands and the site symmetry of the local environment of Dy3+ ion. If the asymmetry around Dy3+ was higher, the value of Ω2 will be high. The Ω2 factor value attributes to the covalency and mechanical deviations in the vicinity of Dy3+ ions whereas, Ω4 factor is a long range effect which dependents on the dielectric and viscosity of the host matrix. Smaller values of Ω4 obtained for ZrO2:Dy3+ NPs shows appreciable rigidity of the crystalline host matrix. Ω6 is the intensity factor which could not be calculated in the present 10


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case because of 4F9/2→6H11/2 transition was very weak. Radiative lifetime, branching ratios and asymmetric ratio were also determined according to the method as reported earlier [39]. The measured branching ratios were found to be 0.99 which was greater than 0.50 as a result; the present phosphor was good source for laser due to its high emission rates. The CIE chromaticity coordinates of the present phosphor were estimated and were very close to the NTSC standard values (Table 4 and Figure.18 (a)). The CCT factor was relating to its color rendering reference light when heated up to a specific temperature, in Kelvin (K). To find quality of white light CCT values were calculated by using McCamy empirical formula [40 42]. Table 4 shows the CCT values estimated were in well acceptable ranges and quite useful in home appliances (Figure. 18 (b)). The list CIE values for doped ZrO2 NPs obtained under different excitation wavelengths were tabulated in Table 5. The detection of LFPs by using luminescent material was a physical phenomenon depends on the sticking nature of phosphor particles to the fingerprint residue [47]. The general mechanism for the revelation of LFPs by using ZrO2:Dy3+ (3 mol %) NP was illustrated in Figure.19. The LFPs was collected from the donor by washing hands thoroughly with soap and were pressed gently on various forensic related materials at RT. The dry ZrO2:Dy3+ (3 mol %) NPs were spread carefully to the area where LFPs were taken and then captured the images using the digital camera. ZrO2:Dy3+ (3 mol %) NP was used for LFPs recognition technique because it exhibited unique property of UV radiation - dependent PL emission and enhanced adhesive property. The non-infiltrating surfaces namely glass, plastic and marble were considered to demonstrate the background interference of the fingerprints stained by ZrO2:Dy3+ (3 mol %) NP (Figure. 20(a –c)). Well-defined minutiae friction ridges can be identified without any background hindrance and color disruption on the fingerprints were shown in Figs. 20 (d- f).

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A series of experiments were carried out on pet bottle, mouse and mobile screen clearly evident well- defined ridge patterns (Figure. 20 (g - i)) without any background interference. Therefore, the optimized compound can be used for revealing the LFPs in a simplistic and adaptable way on various surfaces as labeling agent due to its small crystalline size and intense photoluminescence property. The LFPs stained by ZrO2:Dy3+ (3 mol %) NP on a glass slide under 254 nm UV light were shown Figure. 21. From the figure, it was confirmed that finger print ridges were clearly noticed minutiae ridges effortlessly. Hence, it was confirmed that, preparation of nanophosphor was quite useful in order to enhance LFPs in different porous and non-porous materials. Table 6 shows different hosts used for develop FPs by different authors. It was successfully demonstrated that the developed LFPs exhibit higher efficiency (because procedure involves simple setup and fast and performed within 5 min) and high sensitivity (because no color hindrance and chemical constituents can be observed) compared to the other reported method. In addition, the prepared compounds can be stored for longer time without any loss of luminescence efficiency. Electrochemical impedance spectroscopy (EIS) was carried out at RT using platinum as counter electrode and silver as reference electrodes. The experiment was carried out in 0.1M NaNO3 test solution for Dy doped ZrO2 NPs with an a.c. bias voltage of 0.005 V in the frequency range from 1Hz to 0.1MHz and the results were as shown in Figure.22. The part of semicircle region in the Nyquist plot signifies high frequency component and a linear region represents a low-frequency component. The diameters estimated were 76, 105, 94, 85, 58 and 73 Ω of the semicircle links to the interfacial charge transfer resistance (Rct). Depending on the Rct, the split-up efficiency between the electrons and holes can be explained clearly. The diameter of charge transfer resistance follows the order: ZrO2:Dy3+11 mol % 6H13/2 4

6

F9/2--> H11/2

Pl Intensity (a.u.)

ZrO2:Dy

351 nm

F9/2--> 6H15/2

3

550

600

650

1

y 3+ co nc e

500

ntr

5 7

450

ati on

3+

ZrO2:Dy (1-11 mol %) Exc= 351 nm 4

PL Intensity (a.u)

1 mol % 3 mol % 5 mol % 7 mol % 9 mol % 11 mol %

9 11

D

Wavelength (nm)

Reactant

Piezoelectric Transducer Titanium Horn

0.9

ZrO2:Dy3+ (1 - 11 mol %)

exi = 351 nm

Gas in/outlet

0.6

CIE Y

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Thermostatic water Reaction Solution

0.3

0.0 0.0

0.2

0.4

0.6

0.8

CIE X

Prepared ZrO2:Dy3+ superstructures showed various morphologies and were useful for WLED’s and for the detection of LFPs on various surfaces.

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Nano Superstructures for

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