Facile combustion based engineering of novel white light emitting Zn2TiO4:Dy 3+ nanophosphors for display and forensic applications

Prashanth, Neodymium doped yttrium aluminate synthesis and optical properties A blue light emitting nanophosphor and its use in advanced forensic analysis, Dyes Pigm. Murukeshan, Fluores[r]

Original Article

Facile combustion based engineering of novel white light emitting

K.M Girisha,b, S.C Prashanthab,c,*, H Nagabhushanad

a Department of Physics, Dayanand Sagar Academy of Technology and Management, Bengaluru 560082, India

b 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

a r t i c l e i n f o

Article history:

Received 18 March 2017

Received in revised form

2 May 2017

Accepted 22 May 2017

Available online xxx

Keywords:

Zn 2 TiO 4 :Dy3þ

Nanophosphor

CIE and CCT

JuddeOfelt

Latent fingerprint

a b s t r a c t

Nanomaterialsfind 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 latentfingerprints and display applications, we explored the super-structures of dysprosium (Dy3þ) doped Zn2TiO4via a facile solution combustion route This method offers new potentials in surface-based science comprising display, latentfingerprint, and luminescent ink for anticounterfeiting applications The characteristic emissions of intra-4f shell Dy3þcations in blue, yellow and red regions corresponding to4F9/2to6H15/2,6H13/2, and6H11/2transitions 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:Dy3þnanophosphors for research in display,fingerprint 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/)

1 Introduction

In recent years, luminescent phosphors have gained particular

attention in white light generation for future technologies such as

electroluminescent devices, integrated optics, biomedical

applica-tions, 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 (RE3þ) 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 (Dy3þ)

is selected as a good activator for the emission of light in blue,

yellow and red regions related to the transitions4F9/2/6H15/2,4F9/

2/6H13/2, and4F9/2/6H11/2, respectively The combination of

these colours leads to white emission, which is suitable for the

manufacture of WLEDs[5,6] It was noticed that the crystal struc-ture 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 variousfields[7] Various methods such as solution combustion, solid-state re-actions, solegel, chemical co-precipitation, hydrothermal, spray paralysis[8e13]etc., have been used for the synthesis of pure and rare earth doped ZnOeTiO2nanophosphors

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 latentfingerprints (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 identi-fying people because of its immutable uniqueness Conventional

* 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.

Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d

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/ ).

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,

re-searchers 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

di-rection 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

op-tions to overhaul such obstacles like low sensitivity and selectivity,

excessive background problem and low contrastfingerprints going

through to make LFPs visible These factors provide new prospects

of nanomaterials in surface science as security inks to guard

high-value merchandise, documents, pharmaceuticals and currency

[20e22] In the present work, we report the structural, optical,

luminescent, photometric and forensic properties of Zn2TiO4:Dy3þ

nanophosphors prepared by a facile solution combustion method

2 Experimental

Zn2TiO4 nanophosphors doped with (1e11 mol%) Dy3 þ 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 CuKaradiation at a wavelength of 1.541Å

with a nickel filter at a scan rate of 2 min1) 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

per-formed in the range 200e800 nm using Shimadzu UVeVis

spec-trophotometer 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™

soft-ware is used for spectral analysis

3 Results and discussion

Powder X-ray diffraction (PXRD) patterns of the prepared

nanophosphors were recorded to study the phase, structure and

influence of the Dy3þions in the host lattice.Fig 1illustrates the

PXRD patterns of Zn2TiO4:Dy3þ(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 Zn2TiO4were estimated to be

7.89Å using 2d sinq¼ nlfor (2 2 0) plane Further, the average

crystallite size and other crystallographic parameters of the

pre-pared nanophosphors were estimated using the following relations

(Scherrer's and WilliamsoneHall method)[24,25]and all the ob-tained results are tabulated inTable 1

D¼ Kl

3 ¼bcosq

n¼ 4

3p
D 2V

bcosq

3 þD sinq

d¼ 1

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 Dy3þ 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-Fig 1 Powder X-ray diffraction patterns of Zn 2 TiO 4 :Dy3þnanophosphors.

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:Dy3þnanophosphor are shown inFig 2a, in

which the intense absorption band in the range 300e400 nm

corresponds to the ligand-to-metal charge-transfer (O2to La3þor

O2to Dy3þ) band, which consists of three absorption bands

situ-ated at 454 nm due to host material, and the other bands observed

were due to the electric dipole (ED) transition from the ground

state6H15/2of Dy3þto the different excited states such as4F9/2,6F7/2,

and6F5/2respectively[28,29]

Further, SchustereKubelkaeMunk (SKM) theory was used to

calculate optical band gap energy (Eg) (Fig 2b) as[30]

FðRÞhn¼ A
hneEg

n

(7) where n is the nature of the sample transition (n¼ 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:

FðRÞ ¼ð1  RÞ2

where K is a molar absorption coefficient and S is the scattering

coefficient The energy gap of Zn2TiO4:Dy3þ (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 3illustrates the excitation spectra of Dy3þ(3 mol%) doped

Zn2TiO4nanophosphor 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 Dy3þ activator, known as a ligand-to-metal

charge-transfer 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 Dy3þto O2charge transfer[31] In addition to

CTB, the excitation bands between 350 and 450 nm were due to fef

transitions of Dy3þions (4f6configuration) in the host lattice The

excitation maxima situated at 420 nm correspond to the electronic

transition6H15/2/4G11/2and the emission spectrum was recorded

with the same excitation energy, since, the wavelength

corre-sponding 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:Dy3þ

(1e11 mol%) nanophosphors were recorded under a 420 nm

excitation energy and the results are shown inFig 4 The three

main emission peaks at 496 (blue region), 572 (yellow region), and 685 nm (red region) corresponding to the transitions 4F9/

2/6H15/2,4F9/2/6H13/2, and4F9/2/6H11/2respectively were the characteristic emissions of Dy3þ luminescence Out of these, the transition 4F9/2 / 6H15/2 is a magnetic dipole and 4F9/

2 / 6H13/2 is due to the hypersensitive transition, which is strongly affected by the crystal field environment [32,33] Dy3þ 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 non-radiative (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 3 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 (Dy3þeDy3þ) interactions The dopant ion was substituted in the host site (Zn2þ) of Zn2TiO4 when the Dy3þwas doped as follows:

2½DyO12 þ ½VZnO12/2½DyO12xþVxZnO12 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 lumines-cence intensity may affect the energy transfer process with Dy3þ ions and Zinc vacancies



VxZnO12 complexþ eexcited/hV1ZnO12

i complex h

V1ZnO12i complexþ eexcited/hV11ZnO12i

complex Fig 6 shows a schematic diagram of the energy transfer be-tween Dy3þions and zinc vacancies (VZn)[34] From the energy match rule, the probable cross-relaxation channels (CRC1, CRC2 and CRC3) for Dy3þ ions were responsible for depopulation of 4F9/2 level:

4F9=2þ6H15=2/6H9=2

6F11=2þ6F5=2

4F9=2þ6H15=2/6H7=2

6F9=2þ6F3=2

4F9=2þ6H15=2/6F1=2þ6H9=2

6F11=2

In this process, the excitation energy was transferred from the higher state Dy3þions into neighbouring Dy3þions, excited from the ground state to the metastable4F9/2level, and then was de-excited via these three cross-relaxation processes Finally, all the

Dy3þ ions would go to their ground states as a result of the quenching of luminescence emission[35,36]

Table 1

Estimated crystallite parameters of Zn 2 TiO 4 :Dy3þnanophosphors.

Crystal planes Crystallite size (nm)

Scherrer's

Dislocation density,

d(10 14 m2)

Micro-strain, 3 (10 3 ) sstress (10 8 Pa) N Crystallite size (nm)

WeH plot

Size-strain (10 4 )

K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 3

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

non-radioactive 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

Rcz2

 3V

4pXcN

1

(9) Fig 2 a) Diffused reflectance spectra of Zn 2 TiO 4 :Dy3þnanophosphors b) Energy gap spectra of Zn 2 TiO 4 :Dy3þnanophosphors.

In the present case, V¼ 604.63 Å3, N¼ 4, Xc¼ 0.03, and Rc¼ 20 Å

which is greater than 5Å, 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]

1

By assumingb(X)Q/3 1, it can be written as[38]

log



1

X

¼ K0Q3log X ðK0¼ log K  logbÞ (11)

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

QE¼ Number of photons emitted

Number of photons absorbed¼Ec Ea

La Lc (12) where Ec is related to the integrated luminescence caused by a

direct excitation, Eais associated with the integrated luminescence

from the empty integrating sphere (blank, without sample), Lais

the integrated excitation profile from the empty integrating sphere,

Lcis the integrated excitation profile when the sample is directly

excited by the incident beam The QE for the Zn2TiO4:Dy3þ(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:Dy3þ [41],

CeO2:Eu3þ[42]and YAlO3:Ho3þ[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

the line strengths of RE3þions, 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 J0in terms of JeO in-tensity parameters can be expressed as

Sed¼ X

l¼2;4

Ul 4j  UðlÞ 40

j 0

2

(13)

For RE3þions, 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

AR¼

(

64p4e2n3 3hð2J þ 1Þ

n

n2þ 22 9

) X

JUJ

UðJÞ 2

(14)

where n is the refractive index of the medium, nðn2þ 2Þ2

=9 is the Lorentz localfield correction,  UðJÞ is the doubly reduced matrix elements and e is the the charge of an electron The total transition probability ATand the radiative lifetime can be estimated by[46]

trad¼ 1

Also, the branching ratio, or the fraction of a population that will decay to a given lower level, can be calculated from

b

4j¼A 4j;4

0

j 0

AT

The calculated values of the JeO parameters for the

Zn2TiO4:Dy3þ nanophosphors are summarized in Table 2 It

is noticed thatU2>U4, which indicates a more symmetric structure

Fig 3 Excitation spectra of Zn 2 TiO 4 :Dy3þnanophosphors.

K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 5

of the environment, the ionic nature of the bonding between the

activator and the surrounding ligands

The optimized Zn2TiO4:Dy3þ(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 thefingers on the surfaces of various substrates systematically and very little

Fig 4 Emission spectra of Zn 2 TiO 4 :Dy3þ(1e11 mol%) nanophosphors: a) 2D view (inset: variation of PL intensity with Dy 3þ concentration), b) 3D view.

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 7

Fig 8depicts a magnified spatial image of the black background

fingerprint developed by Zn2TiO4:Dy3þnanophosphor The white

luminescent nanophosphor was checked for being used in the latent fingerprint identification and the image shows a better contrast to the ridges offinger 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

Fig 5 Energy level diagram indicating emission probabilities of Dy3þin Zn 2 TiO 4 nanophosphors.

Fig 6 Schematic diagram of the energy transfer mechanism between Dy3þions and zinc vacancies in the Zn 2 TiO 4 :Dy3þnanophosphors.

K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 7

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 un-changeable for individuals like fingerprints, due to which lip grooves, provides information and evidence in personal identi fica-tion, 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, unde-termined and the general pattern of lip print is shown inFig 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 pat-terns 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

Table 2

JuddeOfelt intensity parameters (U2 , U4 ), radiative transition probability (A T ),

calculated radiative (trad) lifetime and branching ratio of Zn 2 TiO 4 :Dy3þ

nanophosphors.

Dy3þconc

(mol%)

JeO intensity parameters

(10 20 cm 2 )

Wavelength (nm)

A T trad

(ms) b

570 689

570 689

570 689

570 689

570 689

570 689

Fig 7 Illustration of the development of latent finger marks using Zn 2 TiO 4 :Dy3þnanophosphors during process.

Fig 8 Magnified spatial images of black background fingerprint.

equations and the calculated coordinates lie in the white region of

the CIE spectra (Fig 10) show a possible candidature for WLEDs

In addition to this, Correlated Colour Temperature (CCT) was

estimated by CIE coordinates, used to define the colour

tempera-ture 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

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 inTable 3

U0¼ 4x

Also, colour purity (CP) was calculated to check the colour po-tentiality[5]of the prepared phosphor as

Fig 9 a) Patterns of lip prints b) Various lip print patterns identified using Zn 2 TiO 4 :Dy3þnanophosphors.

K.M Girish et al / Journal of Science: Advanced Materials and Devices xxx (2017) 1e11 9

color purity¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

ðxs xiÞ2þ ðys yiÞ2

q

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

ðxd xiÞ2þ ðyd yiÞ2

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:Dy3þ(1e11 mol%) nanophosphors was found to be in the

range of 10e15%, which is close to the white light source, indicating

that the Dy3þdoped Zn2TiO4phosphor is a prominent candidate for

use in WLEDs and display applications

4 Conclusion

Zn2TiO4:Dy3þ (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

reflec-tance studies was shown to correspond to the ligand-to-metal

charge-transfer (O2to Zn2þor O2to Dy3þ) band All the

charac-teristic emissions 4F9/2 / 6Hj (j¼15/2, 13/2, 11/2) of Dy3þ 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

appli-cations From the CIE chromaticity coordinates, the detection of

fingerprint marks on different surfaces and lip print images

in-dicates that Zn2TiO4:Dy3þis very promising for warm WLEDs, solid

state lighting, forensic sciences and Cheiloscopy applications

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Fig 10 CIE diagram of Zn 2 TiO 4 :Dy3þ(1e11 mol%) nanophosphors.

Table 3

Photometric characteristics of the Zn 2 TiO 4 :Dy3þnanophosphors.

Phosphor Concentration

(mol%)

CIE coordinates CCT coordinates Average

CCT (K)

Zn 2 TiO 4 :Dy3þ 1 0.36905 0.40246 0.20817 0.51078 4449

3 0.36593 0.40153 0.20655 0.50995

5 0.36961 0.40885 0.20628 0.51342

7 0.36600 0.40119 0.20671 0.50982

9 0.36635 0.40156 0.2068 0.51002

11 0.36874 0.40184 0.20636 0.50991

Mg SiO :Cr3ỵnanophosphors for solid state lighting... Zn2TiO4:Dy3ỵis very promising for warm WLEDs, solid

state lighting, forensic sciences and Cheiloscopy applications

References

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