Facile combustion based engineering of novel white light emitting zn2tio4 dy 3+ nanophosphors for display and forensic applications

Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Facile combustion based engineering of novel white light emitting Zn2TiO4:Dy3ỵ nanophosphors for display and forensic applications K.M Girish a, b, S.C Prashantha b, c, *, H Nagabhushana d a Department of Physics, Dayanand Sagar Academy of Technology and Management, Bengaluru 560082, India Research and Development Center, Bharathiar University, Coimbatore 641046, India c Research Center, Department of Science, East West Institute of Technology, VTU, Bengaluru 560091, India d Prof CNR Rao Center for Advanced Materials, Tumkur University, Tumkur 572103, India b a r t i c l e i n f o a b s t r a c t Article history: Received 18 March 2017 Received in revised form May 2017 Accepted 22 May 2017 Available online xxx Nanomaterials find a wide range of applications in surface based nanoscience and technology To pass high backward encumbrance, low sensitivity, complicated setup and poor universality in traditional methods for the enhancement of latent fingerprints and display applications, we explored the superstructures of dysprosium (Dy3ỵ) doped Zn2TiO4 via a facile solution combustion route This method offers new potentials in surface-based science comprising display, latent fingerprint, and luminescent ink for anticounterfeiting applications The characteristic emissions of intra-4f shell Dy3ỵ cations in blue, yellow and red regions corresponding to 4F9/2 to 6H15/2, 6H13/2, and 6H11/2 transitions respectively, showed white emission, and the JuddeOfelt theory was used to estimate photometric parameters Concentration quenching phenomenon is discussed based on possible interactions Our study reveals a new prospect of using optimized Zn2TiO4:Dy3ỵ nanophosphors for research in display, ngerprint detection, cheiloscopy, anti-counterfeiting technology, ceramic pigment and forensic applications © 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/) Keywords: Zn2TiO4:Dy3ỵ Nanophosphor CIE and CCT JuddeOfelt Latent fingerprint Introduction In recent years, luminescent phosphors have gained particular attention in white light generation for future technologies such as electroluminescent devices, integrated optics, biomedical applications, displays, X-ray detectors, solar cells, solid-state lighting, liquid crystal back lights, and white light emitting diodes (WLEDs), due to their energy efficiency, long lifetime and environmentally friendly properties [1e4] Trivalent rare earth (RE3ỵ) cations are used as the luminescent activators to convert Ultraviolet (UV), Near ultraviolet (NUV) or blue light radiation to visible light due to their 4f / 4f or 4f / 5d transitions Among the trivalent rare earth ions, dysprosium (Dy3ỵ) is selected as a good activator for the emission of light in blue, yellow and red regions related to the transitions 4F9/2 / 6H15/2, 4F9/ 6 / H13/2, and F9/2 / H11/2, respectively The combination of these colours leads to white emission, which is suitable for the * Corresponding author Research Center, Department of Science, East West Institute of Technology, VTU, Bengaluru 560091, India E-mail address: scphysics@gmail.com (S.C Prashantha) Peer review under responsibility of Vietnam National University, Hanoi manufacture of WLEDs [5,6] It was noticed that the crystal structure of the host lattice and dopant ion plays a major role on the luminescence properties of the phosphor In this manner, titanium based inorganic materials have been studied vigorously due to their excellent properties and potential applications in various fields [7] Various methods such as solution combustion, solid-state reactions, solegel, chemical co-precipitation, hydrothermal, spray paralysis [8e13] etc., have been used for the synthesis of pure and rare earth doped ZnOeTiO2 nanophosphors Forgery was an ever developing global crisis that encountered systems Anticounterfeiting methods that make specific items more difficult to repeat, and simpler approaches to validate them were consequently primary for the fortification of manufacturers and priceless documents Several efforts have been made worldwide to protect things and currencies from being forged Though they have obtained positive results, improvement is still needed in fabrication and design of security ink to prevent faking Currently, a couple of approaches have been used to make latent fingerprints (LFPs), since LFPs provide body proof for identification of individuals in against the crime spot [14] Fingerprint detection was known as a good method for identifying people because of its immutable uniqueness Conventional http://dx.doi.org/10.1016/j.jsamd.2017.05.011 2468-2179/© 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/) Please cite this article in press as: K.M Girish, et al., Facile combustion based engineering of novel white light emitting Zn2TiO4:Dy3ỵ nanophosphors for display and forensic applications, Journal of Science: Advanced Materials and Devices (2017), http://dx.doi.org/10.1016/ j.jsamd.2017.05.011 K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 fingerprint materials (ferric oxide, TiO2, rosin lead, gold and silver) were unable to develop latent detection on some difficult surfaces in the form of powder or suspension, such as rough materials, fabrics, wetted materials and adhesives [15,16] Recently, researchers using powders based on luminescent nanophosphors in order to overcome such difficulties due to their biocompatibility, low toxicity and observed that an enormous progress in this direction on personal identification for forensic purposes [17e19] Amongst, powder dusting process is used as the easiest and commonly encountered system for enhancement of LFPs in a short interval of time and with none elaborate requisites The size and shape-tunable luminescent nano powders have been talents options to overhaul such obstacles like low sensitivity and selectivity, excessive background problem and low contrast fingerprints going through to make LFPs visible These factors provide new prospects of nanomaterials in surface science as security inks to guard highvalue merchandise, documents, pharmaceuticals and currency [20e22] In the present work, we report the structural, optical, luminescent, photometric and forensic properties of Zn2TiO4:Dy3ỵ nanophosphors prepared by a facile solution combustion method Experimental Zn2TiO4 nanophosphors doped with (1e11 mol%) Dy3ỵ were prepared by the solution combustion method using Zinc nitrate [(Zn(NO3)2$6H2O)], tetra butyl titanate [TiO (NO3)2], Dysprosium nitrate [Dy(NO3)2] as analytical reagents and oxalyl di-hydrozide (ODH) [C2H6N4O2] as a fuel The stoichiometric ratios of analytical reagents and fuel with minimum quantity of double ionized water were mixed well in a petri dish using magnetic stirrer and the dish containing a homogeneous mixture was placed in a pre-heated muffle furnace The solution boiled and catched the fire after dehydration gave white powder finally Details of the synthesis procedure have been reported elsewhere [23] The crystalline nature of the powder samples is characterized by PXRD using X-ray diffractometer (Shimadzu) (operating at 50 kV and 20 mA by means of CuKa radiation at a wavelength of 1.541 Å with a nickel filter at a scan rate of 2 minÀ1) The surface morphology of the product is examined by Hitachi table top (SEM) (Model TM 3000) (accelerating voltage up to 20 kV using Tungsten filament) Transmission Electron Microscopy (TEM) analysis is performed on a JEOL, JEM-2100 (accelerating voltage up to 200 kV, LaB6 filament) equipped with EDS having 1.5 Å resolutions The diffuse reflectance (DR) spectral studies of the samples are performed in the range 200e800 nm using Shimadzu UVeVis spectrophotometer model 2600 Photoluminescence studies are made using Horiba (model Fluorolog-3) Spectrofluorimeter at RT using 450 W xenon lamp as an excitation source Fluor Essence™ software is used for spectral analysis Results and discussion Powder X-ray diffraction (PXRD) patterns of the prepared nanophosphors were recorded to study the phase, structure and inuence of the Dy3ỵ ions in the host lattice Fig illustrates the PXRD patterns of Zn2TiO4:Dy3ỵ (1 mol%), which show the highly crystalline single phase cubic structure with JCPDS Card No 77-14 (space group Fd-3m (No 227)) and no additional peaks, confirming that the dopant cations were well capped into the host lattice Similar results were also observed for other concentrations which well match with our earlier report [23] The lattice parameters for cubic Zn2TiO4 were estimated to be 7.89 Å using 2d sin q ¼ nl for (2 0) plane Further, the average crystallite size and other crystallographic parameters of the prepared nanophosphors were estimated using the following relations Fig Powder X-ray diffraction patterns of Zn2TiO4:Dy3ỵ nanophosphors (Scherrer's and WilliamsoneHall method) [24,25] and all the obtained results are tabulated in Table D¼ ¼ n¼ Kl b cos q b cos q 3p ÀDÁ (1) (2) (3) 2V b cos q D sin q ẳ ỵ l l (4) D2 (5) sstress ¼ E (6) d¼ Electron microscopy was carried out to investigate the surface morphology, orientation, size and structures of nano particles in the prepared sample It is clear from SEM images (not given here) that Dy3ỵ activated Zn2TiO4 nanophosphors consists of cracks, pores, agglomerates, irregular morphology and large voids, due to escape of a large amount of gases with high pressure during combustion reaction [23,26] TEM, SAED and HRTEM images (not given here) show the prepared samples are with an average size in the range 20e100 nm, having polycrystalline nature (distinct ring patterns) [27], and the high crystallinity was evidenced by the well- Please cite this article in press as: K.M Girish, et al., Facile combustion based engineering of novel white light emitting Zn2TiO4:Dy3ỵ nanophosphors for display and forensic applications, Journal of Science: Advanced Materials and Devices (2017), http://dx.doi.org/10.1016/ j.jsamd.2017.05.011 K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 Table Estimated crystallite parameters of Zn2TiO4:Dy3ỵ nanophosphors Crystal planes Crystallite size (nm) Scherrer's Dislocation density, d (Â1014 mÀ2) Micro-strain, 220 311 400 422 511 440 44 42 34 33 31 31 5.1 5.6 8.6 9.1 10.0 10.0 0.75 0.78 0.97 1.00 1.07 1.08 defined lattice fringe patterns with a fringe width ~0.279 nm for (202) plane which was close to the calculated value of 0.278 nm Diffused reflectance spectroscopy (DRS) was performed for prepared dry powders to overcome the dispersed method which was popular in conventional UVeVis absorption spectroscopy The DR spectra of Zn2TiO4:Dy3ỵ nanophosphor are shown in Fig 2a, in which the intense absorption band in the range 300e400 nm corresponds to the ligand-to-metal charge-transfer (O2À to La3ỵ or O2 to Dy3ỵ) band, which consists of three absorption bands situated at 454 nm due to host material, and the other bands observed were due to the electric dipole (ED) transition from the ground state 6H15/2 of Dy3ỵ to the different excited states such as 4F9/2, 6F7/2, and 6F5/2 respectively [28,29] Further, SchustereKubelkaeMunk (SKM) theory was used to calculate optical band gap energy (Eg) (Fig 2b) as [30] n FRịhn ẳ A hneEg (7) where n is the nature of the sample transition (n ¼ 1/2, 2, 3/2, 3; direct allowed, indirect allowed, direct forbidden, indirect forbidden transitions respectively) and F(R) is KubelkaeMunk function, which can be calculated by using the following equation: FRị ẳ Rị2 K ẳ S 2R (8) where K is a molar absorption coefficient and S is the scattering coefficient The energy gap of Zn2TiO4:Dy3ỵ (1e11 mol%) was determined to be in the range 3.13e3.18 eV, which indicates that the present material has a suitable energy gap to create excited electronehole pairs, leading to an improved photoluminescence [30] Fig illustrates the excitation spectra of Dy3ỵ (3 mol%) doped Zn2TiO4 nanophosphor The spectrum was composed of two parts: the broadband in the range 250e350 nm was the charge transfer band (CTB) due to the electronic excitation of O(2p) to the empty 4f orbital of Dy3ỵ activator, known as a ligand-to-metal chargetransfer transition (LMCT), which was then resolved into three Gaussian peaks due to (a) the band to band transition, (b) the ZneO charge transfer band (O2p electron occupy one of the empty Zn orbital), and (c) the Dy3ỵ to O2 charge transfer [31] In addition to CTB, the excitation bands between 350 and 450 nm were due to fef transitions of Dy3ỵ ions (4f6 conguration) in the host lattice The excitation maxima situated at 420 nm correspond to the electronic transition 6H15/2 / 4G11/2 and the emission spectrum was recorded with the same excitation energy, since, the wavelength corresponding to the intense excitation band can give intense emissions It shows that the present nanophosphor can be effectively excited by energies in the visible region, which is useful for fabrication of WLEDs Characteristic emission probabilities of Zn2TiO4:Dy3ỵ (1e11 mol%) nanophosphors were recorded under a 420 nm excitation energy and the results are shown in Fig The three (Â10À3) sstress (Â108 Pa) N Crystallite size (nm) WeH plot Size-strain (Â10À4) 1.35 1.40 1.74 1.80 1.92 1.94 11.84 12.40 15.32 15.79 16.81 16.81 ~20 ~13 main emission peaks at 496 (blue region), 572 (yellow region), and 685 nm (red region) corresponding to the transitions 4F9/ 6 / H15/2, F9/2 / H13/2, and F9/2 / H11/2 respectively were the characteristic emissions of Dy3ỵ luminescence Out of these, the transition 4F9/2 / 6H15/2 is a magnetic dipole and 4F9/ / H13/2 is due to the hypersensitive transition, which is strongly affected by the crystal eld environment [32,33] Dy3ỵ ions absorb the energy and get excited to the metastable excited states from the ground state, and after the excitation, part of the electrons was depopulated into the 4F9/2 level giving nonradiative (NR) transitions while the rest was depopulated as mentioned (Fig 5) It can be observed that the intensity of the emission peak increased with the increase of dopant concentration up to mol% and diminished beyond this concentration, due to concentration quenching The marvel of concentration quenching is expected to occur in a non-radioactive resonance energy transfer process by the creation of ion vacancies between the neighbouring dopant ions and the host matrix or due to multipolar (Dy3ỵeDy3ỵ) interactions The dopant ion was substituted in the host site (Zn2ỵ) of Zn2TiO4 when the Dy3ỵ was doped as follows: 2ẵDyO12 ỵ ẵVZn O12 /2ẵDyO12 x ỵ VxZn O12 where [DyO12] is a donor while, [VznO12] is an acceptor The following equations indicate self-trapping of electrons after exciting the prepared sample, which suggesting that the luminescence intensity may affect the energy transfer process with Dy3ỵ ions and Zinc vacancies  VxZn O12 à complex h i V1Zn O12 complex i h ỵ e excited/ V1Zn O12 complex i h ỵ e excited/ V11 Zn O12 complex Fig shows a schematic diagram of the energy transfer between Dy3ỵ ions and zinc vacancies (VZn) [34] From the energy match rule, the probable cross-relaxation channels (CRC1, CRC2 and CRC3) for Dy3ỵ ions were responsible for depopulation of 4F9/2 level: F9=2 ỵ H15=2 /6 H9=2 F9=2 ỵ H15=2 /6 H7=2 F9=2 ỵ H15=2 /6 F1=2 ỵ H9=2 F11=2 ỵ F5=2 F9=2 ỵ F3=2 F11=2 In this process, the excitation energy was transferred from the higher state Dy3ỵ ions into neighbouring Dy3ỵ ions, excited from the ground state to the metastable 4F9/2 level, and then was deexcited via these three cross-relaxation processes Finally, all the Dy3ỵ ions would go to their ground states as a result of the quenching of luminescence emission [35,36] Please cite this article in press as: K.M Girish, et al., Facile combustion based engineering of novel white light emitting Zn2TiO4:Dy3ỵ nanophosphors for display and forensic applications, Journal of Science: Advanced Materials and Devices (2017), http://dx.doi.org/10.1016/ j.jsamd.2017.05.011 K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 Fig a) Diffused reectance spectra of Zn2TiO4:Dy3ỵ nanophosphors b) Energy gap spectra of Zn2TiO4:Dy3ỵ nanophosphors Generally, the energy transfer without radiation occurs due to the exchange or multipoleemultipole interaction among dopant ions, the gap among the activator ions reduces at higher dopant density, leading to the decrease of emission intensity due to a nonradioactive energy transfer For this kind of energy transfer mechanism, it is essential to calculate the critical distance (Rc) between the dopant ions and can be estimated as Rc z2 3V 4pXc N !1 (9) Please cite this article in press as: K.M Girish, et al., Facile combustion based engineering of novel white light emitting Zn2TiO4:Dy3ỵ nanophosphors for display and forensic applications, Journal of Science: Advanced Materials and Devices (2017), http://dx.doi.org/10.1016/ j.jsamd.2017.05.011 K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 Fig Excitation spectra of Zn2TiO4:Dy3ỵ nanophosphors In the present case, V ¼ 604.63 Å3, N ¼ 4, Xc ¼ 0.03, and Rc ¼ 20 Å which is greater than Å, indicating that multipolar interaction is responsible for the concentration quenching in the present nanophosphor Dexter theory was used to examine the exact kind of interaction involved in the quenching mechanism [37] the line strengths of RE3ỵ ions, and their radiative transitions are predominately ED in nature because the transitions of MD are much smaller than the forced ED transitions As a result, MD transitions are often neglected in the JeO calculations The line strength of the ED transition between J and J0 in terms of JeO intensity parameters can be expressed as h i Q 1 ẳ k ỵ bXị X Sed ¼ (10) l¼2;4 By assuming b(X)Q/3 ) 1, it can be written as [38]   Q ¼ K À log X log X ðK ¼ log K À log bÞ (11) Number of photons emitted Ec À Ea ¼ Number of photons absorbed La À Lc    2  Ul 4j U ðlÞ 40j0 (13) For RE3ỵ ions, it was essential to estimate radiative transition probabilities and radiative lifetime The total transition probability of spontaneous emission from a level of angular momentum J is À Á2 ) X  2 64p4 e2 n3 n n2 ỵ U Jị  3h2J ỵ 1ị ( by the plot of log I/X vs log X, the value of Q was found to be 6.4 (z6) This indicates that the dipoleedipole interaction plays a role in the concentration quenching The method described by De Mello and Palsson [39,40] was used to calculate the quantum efficiency (QE) of the optimized phosphor QE ¼ X (12) where Ec is related to the integrated luminescence caused by a direct excitation, Ea is associated with the integrated luminescence from the empty integrating sphere (blank, without sample), La is the integrated excitation profile from the empty integrating sphere, Lc is the integrated excitation profile when the sample is directly excited by the incident beam The QE for the Zn2TiO4:Dy3ỵ (3 mol%) phosphor was estimated by the integrated emission counts from the 450 to 700 nm The value was found to be ~58%, indicating the high QE of the present sample In our previous studies, the high QE was also found to be 56%, 65% and 61% for MgO:Dy3ỵ [41], CeO2:Eu3ỵ [42] and YAlO3:Ho3ỵ [43] respectively The JuddeOfelt (JeO) theory has a significant achievement in the explanation of radiative transitions in rare-earth doped different host materials [44,45] The electric-dipole (ED) and magnetic-dipole (MD) transitions are generally used to estimate AR ¼ (14) J UJ where n is the refractive index of the medium, nn2 ỵ 2ị2 =9 is the    Lorentz local field correction, U ðJÞ  is the doubly reduced matrix elements and e is the the charge of an electron The total transition probability AT and the radiative lifetime can be estimated by [46] AT ¼ X trad ¼ AR AT (15) (16) Also, the branching ratio, or the fraction of a population that will decay to a given lower level, can be calculated from   À Á A 4j; 4j0 À Á b 4j ¼ AT 4j; (17) The calculated values of the JeO parameters for the Zn2TiO4:Dy3ỵ nanophosphors are summarized in Table It is noticed that U2 > U4, which indicates a more symmetric structure Please cite this article in press as: K.M Girish, et al., Facile combustion based engineering of novel white light emitting Zn2TiO4:Dy3ỵ nanophosphors for display and forensic applications, Journal of Science: Advanced Materials and Devices (2017), http://dx.doi.org/10.1016/ j.jsamd.2017.05.011 K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 Fig Emission spectra of Zn2TiO4:Dy3ỵ (1e11 mol%) nanophosphors: a) 2D view (inset: variation of PL intensity with Dy3ỵ concentration), b) 3D view of the environment, the ionic nature of the bonding between the activator and the surrounding ligands The optimized Zn2TiO4:Dy3ỵ (3 mol%) nanophosphor may be utilized as a luminous naming marker for an upgraded latent fingerprint detection on an assortment of surfaces in forensic science for individual identification Initially, the finger marks were collected from the washed hand by pressing the fingers on the surfaces of various substrates systematically and very little Please cite this article in press as: K.M Girish, et al., Facile combustion based engineering of novel white light emitting Zn2TiO4:Dy3ỵ nanophosphors for display and forensic applications, Journal of Science: Advanced Materials and Devices (2017), http://dx.doi.org/10.1016/ j.jsamd.2017.05.011 K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 Fig Energy level diagram indicating emission probabilities of Dy3ỵ in Zn2TiO4 nanophosphors Fig Schematic diagram of the energy transfer mechanism between Dy3ỵ ions and zinc vacancies in the Zn2TiO4:Dy3ỵ nanophosphors amount of the prepared sample was sprinkled on the substrate, when the sprinkled substrate exposed to UV light reveals the finger impression giving intense white emission as shown in Fig Fig depicts a magnified spatial image of the black background fingerprint developed by Zn2TiO4:Dy3ỵ nanophosphor The white luminescent nanophosphor was checked for being used in the latent fingerprint identification and the image shows a better contrast to the ridges of finger mark with the background, since the particles were nano in size as confirmed by TEM [47] It consists of clear ridges and mainly secondary details like ridge termination, ridge splitting, crossover and, lake bifurcation which are unique to Please cite this article in press as: K.M Girish, et al., Facile combustion based engineering of novel white light emitting Zn2TiO4:Dy3ỵ nanophosphors for display and forensic applications, Journal of Science: Advanced Materials and Devices (2017), http://dx.doi.org/10.1016/ j.jsamd.2017.05.011 K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 Table JuddeOfelt intensity parameters (U2, U4), radiative transition probability (AT), calculated radiative (trad) lifetime and branching ratio of Zn2TiO4:Dy3ỵ nanophosphors Dy3ỵ conc (mol%) JeO intensity parameters (1020 cm2) U2 U4 2.77 1.68 2.89 1.78 2.81 1.69 2.69 1.64 2.75 1.67 11 2.75 1.67 trad b Wavelength (nm) AT 495 570 689 495 570 689 495 570 689 495 570 689 495 570 689 495 570 689 31 3.2 74.1 33 3.0 74.5 32 3.1 73.6 30 3.3 76.0 31 3.2 75.2 31 3.2 74.6 (ms) form the basics of personal identification and are helpful in the identification of fingerprints [17,18] Further, it is noticed that lip prints are permanent and unchangeable for individuals like fingerprints, due to which lip grooves, provides information and evidence in personal identification, criminal investigation in dentistry, sex determination and age estimation Lip prints were used in Cheiloscopy to identify persons on the basis of the arrangement of lines on red parts of the lips [48,49] Lip prints were labeled based on geometric dominance of lines present like vertical, intersected, branched, reticular, undetermined and the general pattern of lip print is shown in Fig 9a Sharma et al noticed that vertical and intersected patterns are dominant in females whereas branched and reticular patterns are predominant in males [50] In the present study, the different patterns on different parts of the lips were identified and, marked as shown in Fig 9b, in which the female dominant nature was observed Generally the colour of the phosphor can be identified by Commission International de I' Eclairage (CIE) colour coordinates The CIE plot is drawn using a colour calculator software, and the CIE coordinates (x, y) can be calculated based on the following Fig Illustration of the development of latent finger marks using Zn2TiO4:Dy3ỵ nanophosphors during process Fig Magnied spatial images of black background fingerprint Please cite this article in press as: K.M Girish, et al., Facile combustion based engineering of novel white light emitting Zn2TiO4:Dy3ỵ nanophosphors for display and forensic applications, Journal of Science: Advanced Materials and Devices (2017), http://dx.doi.org/10.1016/ j.jsamd.2017.05.011 K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 Fig a) Patterns of lip prints b) Various lip print patterns identified using Zn2TiO4:Dy3ỵ nanophosphors (18) chromaticity diagram, the average CCT was found to be 4499 K, indicating the warm white light used for residence appliances, since it is less than 5000 K [51,52] and all the photometric values are summarized in Table (19) U0 ẳ 4x 2x ỵ 12y ỵ (20) V0 ẳ 9y 2x ỵ 12y ỵ (21) equations and the calculated coordinates lie in the white region of the CIE spectra (Fig 10) show a possible candidature for WLEDs X XỵY ỵZ Y yẳ XỵY ỵZ xẳ In addition to this, Correlated Colour Temperature (CCT) was estimated by CIE coordinates, used to define the colour temperature of a light source CCT was calculated by transforming the (x, y) coordinates of the light source to (U0 , V0 ) using the following equations By determining the temperature of the closest point of the Planckian locus to the light source on the (U0 , V0 ) uniform Also, colour purity (CP) was calculated to check the colour potentiality [5] of the prepared phosphor as Please cite this article in press as: K.M Girish, et al., Facile combustion based engineering of novel white light emitting Zn2TiO4:Dy3ỵ nanophosphors for display and forensic applications, Journal of Science: Advanced Materials and Devices (2017), http://dx.doi.org/10.1016/ j.jsamd.2017.05.011 10 K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 Fig 10 CIE diagram of Zn2TiO4:Dy3ỵ (1e11 mol%) nanophosphors Table Photometric characteristics of the Zn2TiO4:Dy3ỵ nanophosphors Phosphor Concentration CIE coordinates (mol%) X Y Zn2TiO4:Dy3ỵ 11 0.36905 0.36593 0.36961 0.36600 0.36635 0.36874 0.40246 0.40153 0.40885 0.40119 0.40156 0.40184 CCT coordinates Average CCT (K) U0 V0 0.20817 0.20655 0.20628 0.20671 0.2068 0.20636 0.51078 4449 0.50995 0.51342 0.50982 0.51002 0.50991 q xs xi ị2 ỵ ys yi Þ2 color purity ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi  100% ðxd À xi ị2 ỵ yd yi ị2 (22) where (xs, ys), (xi, yi) and (xd, yd) are the chromaticity coordinates of the sample point, coordinates of the illuminant point, and the dominant wavelength point respectively The CP of Zn2TiO4:Dy3ỵ(1e11 mol%) nanophosphors was found to be in the range of 10e15%, which is close to the white light source, indicating that the Dy3ỵ doped Zn2TiO4 phosphor is a prominent candidate for use in WLEDs and display applications Conclusion Zn2TiO4:Dy3ỵ (1e11 mol%) nanophosphors were successfully prepared by the facile solution combustion method Pure, single cubic phase, porous, agglomerated and nanocrystallites were confirmed by PXRD and electron microscopy studies The intense absorption band in the range 300e400 nm in the diffused reflectance studies was shown to correspond to the ligand-to-metal charge-transfer (O2À to Zn2ỵ or O2 to Dy3ỵ) band All the characteristic emissions 4F9/2 / 6Hj (jẳ15/2, 13/2, 11/2) of Dy3ỵ ion in a Zn2TiO4 matrix were confirmed by the PL emission studies The estimated branching ratio was found to be ~74%, indicating the usefulness of the present nanophosphor for display device applications From the CIE chromaticity coordinates, the detection of fingerprint marks on different surfaces and lip print images indicates that Zn2TiO4:Dy3ỵ is 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Girish, et al., Facile combustion based engineering of novel white light emitting Zn2TiO4: Dy3 ỵ nanophosphors for display and forensic applications, Journal of Science: Advanced Materials and Devices... Girish, et al., Facile combustion based engineering of novel white light emitting Zn2TiO4: Dy3 ỵ nanophosphors for display and forensic applications, Journal of Science: Advanced Materials and Devices... Girish, et al., Facile combustion based engineering of novel white light emitting Zn2TiO4: Dy3 ỵ nanophosphors for display and forensic applications, Journal of Science: Advanced Materials and Devices