solid BaTiO3:Dy3+ microspheres and their applications in effective detection of latent fingerprints and lip prints

LFPs were visualized using an optimized powder undoubtedly with high contrast, selectivity and low background interference on various porous and non-porous surfaces.. The photometric stu[r]

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M Dhanalakshmia,b, H Nagabhushanac,*, G.P Darshand, R.B Basavarajc,

B Daruka Prasade

aDepartment of Physics, Govt Science College, Bengaluru 560 001, India

bResearch and Development Center, Bharathiar University, Coimbatore 641046, India cProf C.N.R Rao Centre for Advanced Materials, Tumkur University, Tumakuru 572103, India dDepartment of Physics, Acharya Institute of Graduate Studies, Bangalore 560 107, India

eDepartment of Physics, BMS Institute of Technology and Management, VTU, Belagavi-afﬁliated, Bangalore 560 064, India

a r t i c l e i n f o

Article history:

Received 19 December 2016 Received in revised form 31 January 2017 Accepted February 2017 Available online 16 February 2017

Keywords:

Sonochemical synthesis Latentﬁngerprint Cheiloscopy JuddeOfelt analysis

a b s t r a c t

Nanostructured materialsfind potential benefits for surface-based science such as latent fingerprints (LFPs) and lip print detection on porous and non-porous surfaces To encounter the drawbacks viz low sensitivity, high background hindrance, complicated procedure and high toxicity associated with traditional uo-rescent powders were resolved by using hollow/solid BaTiO3:Dy3ỵ(1e5 mol %) microspheres The

visu-alization of LFPs stained by the optimized BaTiO3:Dy3ỵ(2 mol %) hollow/solid microspheres exhibits

well-dened ridge patterns with high sensitivity, low background hindrance, high efﬁciency and low toxicity on various surfaces The powder X-ray diffraction results revealed the body centered cubic phase of the pre-pared samples The emission spectra exhibit intensive peaks at ~480, 575, and 637 nm, which were attributed to transitions4F

9/2/6HJ(J¼ 15/2, 13/2, 11/2) of Dy3ỵions, respectively Surface morphologies

were extensively studied with different sonication times and concentrations of the used barbituric acid The Commission International De I-Eclairage (CIE) and Correlated Color Temperature (CCT) analyses revealed that the present phosphor is highly useful for the fabrication of white light emitting diodes © 2017 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi

This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

1 Introduction

In a crime spot investigation, LFPs are the most important physical evidence for identification of criminals [1,2] When a criminal touches any surface in a spot, skin sweat transferred to the surface through pores leading to an invisible ridge pattern is well known as latentfingerprints In a forensic analysis, LFPs are the most influential method due to its unique and immutable features[3,4] Because of invisibility of LFPs, enhancement of LFPs was required for identification and visualization Nowadays, several methods have been used to make LFPs visible Among them, the powder dusting method allows for LFPs to be visualized within a short period of time and without any complicated requirements The conventional dusting powders were mainly classified into regular, metallic and

luminescent materials Regular and metallic powders constituent of resinous polymers and meshed metals which are hazard to in-vestigators' health[5] These conventional powders are not capable of enhancing LFPs on some complicated surfaces Luminescent nanopowders are potential solutions to overtake such limitations, making LFPs visible Luminescent nanopowders were explored as labeling agents for visualization of LFPs and exhibit good contrast, sensitivity and adhesion efﬁciency These factors provide new possible applications of nano powders in surface science

In addition, lip prints are form of wrinkles and grooves including normal lines,ﬁssures and are present in the zone of transition of human lip between the inner labial mucosa and outer skin[6] Lip prints are also a main evidence for identiﬁcation of an individual in a forensic dentistry due to its uniqueness, except in monozygotic twins The revelation of lip prints was well known as cheiloscopy

[7] The cheiloscopy plays a major role in forensic science for person identiﬁcation in crime investigations, ethnic studies, mass di-sasters,ﬁre victims, and vehicle accidents

* Corresponding author

E-mail address:bhushanvlc@gmail.com(H Nagabhushana)

Peer review under responsibility of Vietnam National University, Hanoi

http://dx.doi.org/10.1016/j.jsamd.2017.02.004

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The ultrasonic sonochemical method has received a great attention for the fabrication of phosphors with unusual and tailored properties Further, an ultrasound assisted synthesis route has great commercial potential advantages with high production rates, syntheticflexibility on choosing host materials as high pu-rity nano powders, rapid reaction rate, narrow size distribution, stable colloidal dispersion, uniform mixing, less synthesis time, and less energy usage[8] In this method, the chemical reactions arise from acoustic cavitations, i.e., formation, growth and implosive collapse of bubbles in the liquid The growth of the bubble happens through the diffusion of solute vapor into the volume of the bubble, while the collapse of the bubble arises when the bubble size reaches its maximum value When the solution was exposed to ultrasound irradiation, the bubbles were implosively collapsed by acousticfields in the solution[9] According to the hot spot theory, very high temperatures (>5000 K) were achieved upon the collapse of a bubble Since this collapse occurs in less than a nanosecond, very high cooling rates (>1010 K/s) was also obtained These extreme environments can drive several chemical reactions and physical modifications occur as a result, allowing shape and size of the phosphors to be effectively tuned[10] There is a pressing need for synthesis of nano/micro structured materials at reasonably low temperature for industrial applications

To the best of our knowledge, there have been no reports on an ultrasound assisted sonochemical method for fabrication of BaTiO3:Dy3ỵ (1e5 mol %) powders using Barbituric acid as a sur-factant The prepared optimized samples were employed to visu-alize LFTs and lip prints on various porous and non-porous surfaces In addition, the structural and photoluminescent properties were analyzed, and photometric properties were systematically studied

2 Experimental

Titanyl nitrate was prepared by taking N-butyl titanate in a petri dish and a minimum quantity of doubled distilled water was added to yield titanyl hydroxide Further, nitric acid was added to this

redox mixture which gave titanyl nitrate The corresponding chemical reactions can be given by[11]

TiOC4H9ị4ỵ 3H2O/TiOOHị2ỵ 4C4H9OH (1)

TiOOHị2ỵ 2HNO3/TiONO3ị2ỵ 2H2O (2)

Stoichiometric amount of barium nitrate and titanyl nitrate were dissolved in 100 ml deionized water and thoroughly mixed in a magnetic stirrer to get uniform solution The stoichiometric amount of dysprosium nitrate (1e5 mol %) was added to the above resultant solution Further, different concentrations of barbituric acid (0.05e0.25% W/V) were added to the resultant mixture slowly Ultrasound irradiation was accomplished with a high-intensity ultrasonic probe (~2.5 cm diameter; Ti horn, 20 kHz, 150 W/cm2) immersed directly in the reaction solution Then, the solution mixture was stirred with high-intensity ul-trasound irradiation under ambient air (the ultrasonic frequency ~ 20 kHz, the power ~ 150 W) at aﬁxed temperature of 75 C and by varying ultrasonic time (1e6 h) The solution was kept undisturbed until a white precipitate was formed The pre-cipitate wasﬁltered and washed several times by using distilled water and ethanol to remove any unreacted material The ob-tained product was dried at 60 C for h in a vacuum oven Finally, the dried precipitate was grinded thoroughly into the powder form and used for further studies

2.1 Characterization

The obtained product was well characterized by using Shimadzu 7000 powder X-ray diffractometer using Cuka radiation Morphology of the product was studied by means of TM 3000, Hitachi table top Scanning electron microscopy and Hitachi H-8100 Transmission electron microscope The Perkin Elmer (Lambda-35) spectrometer was used to study the reﬂectance of the samples For

Fig Fingerprints on the surface of glass stained by (a) TiO2powder (b) BaTiO3:Dy3ỵ2 mol % powder, (c) Fe2O3powder, and (d) BaTiO3:Dy3ỵpowder synthesized by mechanical

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PL measurements Jobin Yvon Spectroﬂourimeter Fluorolog-3 operational with 450 W Xenon lamp was used

2.2 Mechanism of visualization of LFPs and lips print using BaTiO3:Dy3ỵhollow/solid microspheres

FPs collected from healthy volunteers with the age group of ~21 years were deposited on porous and non-porous surfaces namely microscopic slides, aluminum foils, scratched CDs, leafs, coins, magazines, pen, colored plastic bag etc Before deposition,ﬁngers of volunteers were thoroughly washed with water and dried in air without touching any surfaces The optimized BaTiO3:Dy3ỵ(2 mol %) powder was carefully sprinkled and gentle dusted uniformly on LFPs using a special“Marabou” feather brush Further, an UV lamp (4 W, 254 nm) was illuminated on the stained LFPs and then pho-tographed using 50 mm f/2.8G ED lens Nikon D3100/AF-S digital camera For visualization of latent lip prints, lips were cleaned

thoroughly using smooth tissue paper and then with sterile cotton The lips were lightly pressed against a glass slab for ~3e5 s The latent lips prints acquired on glass slab were visualized by spraying the optimized powder with a smooth brushing method and pho-tographed using a digital camera

3 Results and discussion

To determine effectiveness and selectivity of the prepared BaTiO3:Dy3ỵ(2 mol %) powder as auorescence labeling agent for the visualization of LFPs on glass slide, conventionally used iron oxide (Fe2O3) and titanium dioxide (TiO2) powders were used as a control It was found that, LFPs developed by Fe2O3, TiO2 and BaTiO3:Dy3ỵpowders fabricated by mechanical stirring could not resolve fullﬁngerprint patterns (Fig 1(a, c& d)) However, LFP stained by BaTiO3:Dy3ỵ(2 mol %) hollow/solid microspheres under 254 nm UV light revealed well deﬁned friction ridges (Fig 1b) It is

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evident that the optimized BaTiO3:Dy3ỵpowder can be used as an effective labeling agent for visualization of LFPs due to their supe-rior white light emission Well deﬁned ﬁngerprint images with high sensitivity were also visualized by BaTiO3:Dy3ỵ(2 mol %) hollow/ solid microspheres on non-porous materials including green leaf, plastic sheet, plastic pen edge, steel pen edge, TV remote, mobile screen, coin, and stainless steel (Fig 2)

In addition, aged (different time periods) LFPs were examined to exhibit the suitability and robustness of the prepared powder in advanced forensic detection.Fig 3(aec) shows the aged LFPs with different time periods (1 day, week, and month) stained by the optimized BaTiO3:Dy3ỵ powder Normally, sensitivity of labeling

powder progressively decreases as aging of the LFPs enhances, due to evaporation of chemical constituents of the LFPs In the present work, even one month aged FP shows defined ridges, indicate the practicability of the prepared powder The LFPs on different textured marbles visualized by optimized BaTiO3:Dy3ỵ(2 mol %) powder under 254 nm illumination demonstrate the well-defined ridge patterns withfine contrast and without or less background hindrance (Fig (def)) The differently magnied SEM images of LFP enhanced by prepared BaTiO3:Dy3ỵ(2 mol %) powder were shown inFig The prepared powder particles provide uniform distribution and stronger adhesive ability via each static and sur-face absorption interactions and it increases the chemical stability,

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permitting the long protection of light and affording afﬁnity with LFPs

The above obtained results demonstrated that, the optimized BaTiO3:Dy3ỵ(2 mol %) powder was explored as an efficient fluo-rescent labeling agent for visualization of LFPs on various porous and non-porous surfaces The prepared optimized powder can visualize LFPs as a whole, with high sensitivity, efficiency and low background interference

Lip prints similar toﬁngerprints have many elevations and de-pressions providing evidence in individual identiﬁcation and criminal investigation in a forensic dentistry The study of such lip prints called as Cheiloscopy Usually, lip prints can be found where the surface in contact with the lips[12] Most commonly in glasses, cigarettes, straws, food items etc However, some extra effort has been required to make lip prints visible Therefore, we explored BaTiO3:Dy3ỵ(2 mol %) powder for visualization of lip prints on glass under UV 254 nm Fig shows the lip print stained by the

optimized BaTiO3:Dy3ỵ(2 mol %) powder From thegure, it was clearly evident that the whole lip prints with Tsuchihashi's Type V, Type I, Type I0and Type III grooves (Fig 5(bee)) were visualized with high sensitivity and contrast due uniform smaller size and adhesive nature of the powder

In the ultrasound assisted sonication method, many experi-mental parameters namely sonication time, concentration of sur-factant, pH value and sonication power etc., may affect greatly the size and morphology of the products In the present study, the morphology of the prepared samples was extensively studied with different sonication times and concentrations of the surfactant.Fig

(aee) shows SEM images of BaTiO3:Dy3ỵ(2 mol %) with different sonication times (1e5 h) with a 0.25% W/V concentrated barbituric acid When the sonication time was ~1 h, several splintered parts having small lotusﬂower e like morphology was observed (Fig

(a)) The petals ofﬂowers started blossoming, when the sonication time was increased to h Further, increase of the sonication time

Fig Differently magniﬁed SEM images of ngerprints stained by BaTiO3:Dy3ỵ(2 mol %) powder ((b) is a magniﬁed portion of (a))

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(4 and h), large number ofﬂowers closed to form a uniform hallow spherical shaped morphology was obtained (Fig 6(d& e)) The obtained spherical morphology preserved even after h sonication irradiation Series of trials were conducted to ascertain the impact of surfactant concentration on theﬂower morphology and are shown inFig 6(fej) When the concentration of barbituric acid was 0.05% W/V, a yolk-shell shaped structure consisting of many particles was observed (Fig 6(f)) A hallow yolk-shell shaped micro structure

appeared, when the concentration of barbituric acid was increased to 0.10% W/V (Fig 6(g)) However, with increase of concentration to 0.15% W/V, more hallow was observed and retained even further extended concentration (0.20% W/V) When the barbituric acid concentration was increased to 0.25% W/V, signiﬁcantly condensed hallow space was observed (Fig 6(j))

Fig 7depicts TEM, HRTEM, SAED patterns, and EDAX images of the BaTiO3:Dy3ỵ(2 mol %) powder The TEM image displays layer

Fig SEM images of BaTiO3:Dy3ỵ(2 mol %) powder with (aee) different sonication times (1e5 h), a barbituric acid concentration of 0.25% W/V, and (fej) different concentrations

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morphology and size ranged from 30 to 50 nm (Fig 7(a)) The lattice spacing (d) was estimated from an HRTEM image (Fig 7(b)) and found to be ~0.26 nm and the value was well matched with PXRD values.Fig 7(c) shows the SAED pattern of the prepared sample and it conﬁrms the polycrystalline nature of the prepared powder Further, elemental compositions such as atomic and molecular weight were obtained from EDAX, which is shown inFig 7(d)

Fig 8(a) shows the PXRD proles of BaTiO3:Dy3ỵ(1e5 mol %) powder fabricated with a h sonication time and barbituric acid (0.25% W/V) The sharp and intense diffraction peaks were in good agreement with the cubic phase with JCPDS no 31-0174 [13] Further, it was observed that small impurity peak of dopant Dy2O3 ions was identiﬁed, indicating the successful substitution of Dy3ỵ ions in the Ba2ỵsites The intensity of impurity peak increases with increasing the concentration of dopant ions

The average crystallite size (D) was estimated using the Scher-rer's formula[14]and listed inTable It was evident from the table that, the variation in crystalline size is dependent on dopant Dy3ỵ concentration This was due to the increase in strain, leading to the replacement of Ba2ỵions by smaller radius Dy3ỵions Generally, broadening of the PXRD peaks was associated with crystallite sizes or the strains present within the sample or both Therefore, the WilliamsoneHall ﬁtting method (Fig (b)) [15]was utilized to estimate the strain induced in the prepared samples and the ob-tained results were given inTable

Fig 8(c) displays the diffuse reﬂectance spectra of the pure and Dy3ỵdoped BaTiO3powders The spectra exhibited peaks at ~1071, 887, 796, 381, 364, 348 and 320 nm, which were due to the 4fe4f transition of the Dy3ỵions[16] The KubelkaeMunk (KeM) theory was utilized to estimate optical energy band gap of BaTiO3:Dy3ỵ (1e5 mol %) powders from the DRS spectra[17] The optical energy band gaps (Eg) values of the prepared powders were shown in

Fig 10(d) and inTable The changes in Egwere mainly ascribed to degree of order and disorder in the matrix as well as variations in distribution of energy levels within the band gap[18]

The PL excitation spectrum of BaTiO3:Dy3ỵ (2 mol %) under 480 nm as emission was shown inFig 9(a) The spectrum exhibited peaks at ~350, 365, 387 and 435 nm, which were attributed to6H15/ / 6P7/2, 6H15/2 / 6P5/2, 6H15/2 / 4I13/2 and 6H15/2 / 4G11/2 respectively.Fig 9(b) shows the PL emission spectra of BaTiO3:Dy3ỵ (1e5 mol %) excited at 387 nm at RT The spectra exhibited distinct emission peaks at ~480, 574 and 637 nm, which were attributed to 4F

9/2/6H15/2,4F9/2/6H13/2and4F9/2/6H11/2respectively[19] From theﬁgure, it was clear that peak at ~574 nm was more prom-inent as compared to other two peaks, which was due to a forced electric dipole transition The peak at ~480 nm was due to magnetic dipole transitions and is much less sensitive to the coordination environment The yellow emission peak at 574 nm (4F9/2/6H13/2) was stronger than the blue emission 480 (4F

9/2/6H15/2), indicating that Dy3ỵwas located in a more non centro-symmetric position in

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the BaTiO3host[20].Fig 9(c) shows the partial energy-level diagram indicating the different excitation and emission mechanism of BaTiO3:Dy3ỵpowder Asymmetry ratio (A21) was used to determine the degree of distortion from the inversion symmetry of the local environment of the Dy3ỵions in a host matrix[21]

A21ẳ H

I2

4F

9=2/6H13=2

dl H

I1

4F

9=2/6H15=2

dl (3)

where I1and I2the intensities of a magnetic dipole transition at 480 nm and the electric dipole transition at 574 nm, respectively The variation of A21 with varying Dy3ỵ concentration in BaTiO3:Dy3ỵ(1e5 mol %) powder was shown inFig 10(a) and its estimated values were listed inTable

The effect of doping concentration (Dy3ỵ) on PL emission in-tensity in the BaTiO3host was shown inFig 10(a) It was clear from the ﬁgure that, the PL intensity increased with an increase of concentration of Dy3ỵup to mol % and afterwards it diminished The decrease in the PL intensity was due to the well-known phe-nomenon called as a self-concentration quenching, resulting from the resonance energy transfer between neighboring Dy3ỵions[22] From energy match rule, cross-relaxation lines among Dy3ỵions are responsible for population decrease of4F9/2level as follows:

4F

9=2ỵ6H15=2/6H9=2

6F

11=2ỵ6F5=2 (4)

4F

9=2ỵ6H15=2/6H7=2

6F

9=2ỵ6F3=2 (5)

4F

9=2ỵ6H15=2/6F1=2

6H 9=2

6F

11=2 (6)

In the above process, the excitation energy was transferred from a Dy3ỵion in a higher excited state to a neighboring Dy3ỵion and promotes the latter from the ground state to the metastable level The Dy3ỵions at4F9/2level undergo de-excitation through a cross relaxation process while Dy3ỵions in the ground state will allow the energies from Dy3ỵat6H15/2level simultaneously Finally, all the Dy3ỵ ions will go in their ground states and thus the lumi-nescence related to4F9/2level was quenched[23]

The non radiative energy transfer among Dy3ỵions leads to a concentration quenching effect By knowing the critical distance (Rc) between the neighboring Dy3ỵions, the type of the interaction mechanism can be explored[24] The calculated value of Rc was found to be ~4.47 Å and was almost equal to Å, which leads to the multipoleemultipole interaction in the BaTiO3host and is the main cause for concentration quenching of Dy3ỵin the powder There were several types of electric multi-polar interactions, which may be possible, namely, dipoleedipole (ded), dipoleequadrupole (deq), quadrupoleequadrupole (qeq), etc[25] Therefore, it was a

Fig (a) PXRD patterns (b) WeH plots, (c) DR spectra and (d) optical band gap plot of pure and BaTiO3:Dy3ỵ(1e5 mol %) powders prepared with a h sonication time and 0.25%

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necessity to know which type of interaction responsible in the energy transfer between Dy3ỵions According to the Dexter and Schulman theory[26], the ratio emission intensity (I) to concen-tration of activator ion follows the equation;

I Xẳ K

h

1ỵbcịQ3 i1

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where X; the activator concentration, Q; a constant of multi-polar interaction and equals 6, 8, or 10 and less than for dipoleedipole; dipoleequadrupole or quadrupoleequadrupole interactions and charge transfer mechanism respectively, and K andb; constants for the given host lattice under the same excitation condition

LogI X¼ A

Q

3log X (8)

whereA ẳ log k logbị.Fig 10(b) shows thetted linear curve of log (I/X) vs log (X) in BaTiO3:Dy3ỵ(1e11 mol %) powder and the value of the slope to be ~1.205 The calculated value Q was found to be 6.346 and was almost equal This result indicates that, the charge transfer mechanism was due to the ded interaction for the concentration quenching in the present powder

The Commission International De I-Eclairage (CIE) chromaticity co-ordinates of the BaTiO3:Dy3ỵ (1e5 mol %) powders were calculated and listed inTable It was noticed that, the CIE co-ordinates for the present powders were located well within the white region (Fig 10(c)) The Correlated Color Temperature (CCT) was estimated by Planckian locus and their values are listed in

Table The quality of the white light in terms of CCT (Fig 10(d)) was also studied using the McCamy empirical theoretical relation

[27] And the color purity of the powder was estimated according to the work[28]and their values are shown inTable These re-sults clearly show that the present powder may be quite useful for solid state lighting applications

The JuddeOfelt (JeO) theory has been widely utilized to study the radiative transitions of rare-earth ions in several host materials

[29] Various radiative properties such as J-O intensity parameters (U2&U4), emission peak wavelengths (lpin nm), radiative tran-sition probability (AT), calculated radiative (trad) lifetime, branching ratio (bR) and asymmetric ratio (A21) were estimated by using the PL emission spectra[30] The relation between radiative emission rates and the integrated emission intensities were estimated by using the equation reported elsewhere[31]

A02;4 A01 ¼

I02;4 I01 ¼

hy01

hy02;4 (9)

Fig (a) PL excitation spectra of BaTiO3:Dy3ỵ(2 mol %) powder atlemi¼ 480 nm; (b) PL emission spectra of BaTiO3:Dy3ỵ(1e5 mol %) powder atlexcẳ 387 nm; and (c) Energy

levels diagram of Dy3ỵdoped BaTiO3powder

Table

Estimated average crystallite size, strain and energy gap (Eg) values of BaTiO3:Dy3ỵ

(1e5 mol %) powders Dy3ỵconc (mol %)

Crystallite size (nm) [DeS approach]

Crystallite size (nm) [WeH approach]

Strain

(104) Eg(eV)

Pure 30 32 1.4 3.20

1 32 38 1.6 3.23

2 35 36 1.3 3.25

3 38 41 1.9 3.26

4 36 39 1.4 3.28

5 34 35 1.6 3.29

Table

Photometric characteristics of doped BaTiO3:Dy3ỵ(1e11 mol %) powders

BaTiO3:Dy3ỵconc

(mol %)

CIE CCT CCT (K) CP (%)

X Y U0 V0

(10)

where I0eJand hn0eJ; integrated emission intensity and energies corresponding to transition4F9/2/6HJ(J¼ 15/2, 13/2 and 11/2) respectively

The radiative emission rates A0eJ(J ¼ 2, 4) related to forced electric dipole transitions can be obtained and written as a function of the J-O intensity parameters:

A0Jịẳ 64p 4w3

J 3h2J ỵ 1ị

nn2ỵ 22

X lẳ2;4

Ul D

7F

9=2UðlÞ6HJE

(10)

where Að0JÞ; the coefﬁcient of spontaneous emission, e; the elec-tronic charge,wJ; the wave number of the corresponding transi-tion, h; the Planck's constant, Smd; the strength of the magnetic

dipole and n; the RI of the prepared sample.D4F

9=2UðlÞ6HJE

; squared reduced matrix element of Dy3ỵions and were 0.2457 and 0.4139 for J¼ and respectively and these values were inde-pendent of the chemical environment Thus, by using Eqs.(9) and (10), the values of U2 and U4 were calculated and listed in

Table The JeO intensity parameters (U2andU4) for different host matrices have been observed[15]and are listed inTable

The total radiative transition probability (ATðjJÞ) can be calcu-lated and expressed as

ATjJị ẳ X

J0

AJJ0 (11)

The radiative lifetime (tradðjJÞ) of an excited state in terms of ATðjJÞ is given by

Fig 10 (a) Effect of concentration of Dy3ỵon the 574 nm emission and the variation of asymmetric ratio in BaTiO3powders, (b) Relation between log(x) and log (I/x), (c) CIE and (d)

CCT diagram of BaTiO3:Dy3ỵ(1e5 mol %) powders

Table

JuddeOfelt intensity parameters (U2,U4), Emission peak wavelengths (lpin nm), radiative transition probability (AT), calculated radiative (trad) lifetime, branching ratio (bR)

and asymmetric ratio (A21) of BaTiO3:Dy3ỵ(1e5 mol %) powder (lexẳ 387 nm)

BaTiO3:Dy3ỵconc

(mol %)

JuddeOfelt intensity parameters (1020cm2)

Emission peak wavelengthlpin nm

AT(s1) trad(ms) bR A21

U2 U4

1 5.96 6.56 575.80 287.3 3.48 0.998 1.373

2 6.30 6.51 575.05 303.9 3.29 0.999 1.460

3 6.47 5.95 576.02 312.0 3.20 0.998 1.488

4 7.04 10.51 576.55 339.6 2.94 0.998 1.612

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The branching ratio (bðjJÞ) of the resultant emission from an excited level to its lower levels was given by the relation[32]

bjJị ẳA

jJ;j0J0 ATjJị

(13)

The radiative properties were calculated and are listed in

Table The variation ofU2 values with Dy3ỵ concentration in-dicates that it was more sensitive to the ligand environment TheU2 parameter value is attributed to the covalency and structural changes in the vicinity of the Dy3ỵion exhibiting a short range effect, whereas theU4parameter was dependent on the viscosity and dielectric constant of the host causing a long range effect The calculated branching ratio was found to be in the range 0.99 0.50, which endorses that the prepared powder can emit intense laser radiation effectively and be suitable for white color displaying devices

4 Conclusion

In summary, the BaTiO3:Dy3ỵ(1e5 mol %) powders were syn-thesized using the ultrasound assisted sonochemical route The PXRD proﬁles indicated that the prepared samples were well crystalline in nature and a single cubic phase From DRS, the optical energy band gaps were estimated to be ~3.20e3.29 eV LFPs were visualized using an optimized powder undoubtedly with high contrast, selectivity and low background interference on various porous and non-porous surfaces The PL emission spectra exhibited intense peaks at ~480, 574, and 637 nm, which were attributed to 4F

9/2/6H15/2,4F9/2/6H13/2and4F9/2/6H11/2respectively The photometric studies (CIE and CCT) suggest that the phosphor is highly useful for the fabrication of near ultraviolet white light emitting diodes (NUV-WLEDs)

Acknowledgements

The author Dr H Nagabhushana thanks VGST, Karnataka for the sanction of this Project

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