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Solid State Sciences 33 (2014) 19e24

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Solid State Sciences

journal homepage: www.elsevier .com/locate/ssscie

Combustion synthesis and luminescent properties of metal yttriumborates M3Y2 (BO3)4:Eu3þ (M ¼ Ba, Sr) for PDPs applications

J.T. Ingle a,*, R.P. Sonekar b, S.K. Omanwar c, Yuhua Wang d, Lei Zhao d

aDepartment of Physics, J.D. Institute of Engineering & Technology, Yavatmal, IndiabDepartment of Physics, G. S. Science, Arts & Commerce College, Khamgaon, IndiacDepartment of Physics, S.G.B.Amravati University, Amravati, IndiadDepartment of Materials Science, School of Physical Science and Technology, Lanzhou University, Lanzhou, PR China

a r t i c l e i n f o

Article history:Received 9 February 2014Received in revised form16 April 2014Accepted 19 April 2014Available online 28 April 2014

Keywords:Borates phosphorCombustion synthesisPhotoluminescencePDPs

* Corresponding author.E-mail address: jitendra.ingle@yahoo.com (J.T. Ing

http://dx.doi.org/10.1016/j.solidstatesciences.2014.04.01293-2558/� 2014 Elsevier Masson SAS. All rights re

a b s t r a c t

The polycrystalline powder samples of Eu3þ activated; mixed metal yttrium borate phosphorsM3Y2(BO3)4 (M ¼ Ba, Sr) with improved color purity of red emission for plasma display panels (PDPs)were prepared by solution combustion technique. The synthesis is based up on the exothermic reactionbetween the fuel (Urea) and oxidizer (Ammonium nitrate) .The heat generated in the reaction is utilizedfor auto combustion of ingredients. The formation of desired product and crystal structure wasconfirmed by powder XRD technique; while particle morphology was studied using FE-SEM. Samplesunder 254 and 147 nm excitation showed intense and pure red emission around 613 nm correspondingto the electric dipole 5D0 /

7F2 transition of Eu3þ, CIE chromaticity coordinates of synthesized phosphorswas found to be (x ¼ 0.67, y ¼ 0.32) close to National Television Standard Committee (NTSC) for red color;found suitable to employ in plasma display panels (PDPs) applications.

� 2014 Elsevier Masson SAS. All rights reserved.

1. Introduction

The plasma display panels (PDP) is a modern and distinguishtechnique to fabricate and developed a media for large formatdisplay; it considerably attract attention of researchers for thedevelopment of next generation display devices, such as highdefinition TV (HDTV), field emissive display (FED), vacuum fluo-rescent display (VFD), color plasma display panels (PDPs) andmercury free lamps, as it provides a full viewing angle, large screen,less energy utilization, stable and enhance performance and oper-ates in entirely non harmful environment of neon and xenon gas[1e4]. In the PDP’s domain the key factors between success andfailure are going to be quality and longevity; both factors directlydepend on luminous efficiency and color rendering which in turndepends on the nature and the quality of the phosphors; further-more it is still possible to improve the color rendering by using newluminescent materials able to have better color coordinates, i.e. acolor more saturated, especially for red component. Amongstborate phosphors (Y, Gd)BO3:Eu is widely used in PDP as a redcomponent. However, in addition to the brightness problem, the

le).

07served.

color purity of (Y, Gd)BO3:Eu cannot satisfy the requirement forapplication in PDPs [5e8]. Accordingly, the main interest has beenpaid in the development of new and efficient VUV excited redphosphors for application in PDP [9e13]. In the present work weundertake preparation of M3Y2(BO3)4:Eu3þ (M ¼ Ba, Sr) by solutioncombustion synthesis and study of photo luminescent propertiesunder UV and VUV excitation.

2. Experimental

2.1. Combustion synthesis of M3Y2(BO3)4:Eu3þ (M ¼ Ba, Sr)

The samples were prepared by a simple solution combustiontechnique [14e18]. The starting ingredients Y(NO3)3 & Eu(NO3)3 (IRLtd.), Ba(NO3)2, Sr(NO3)2, H3BO3, NH4NO3 & NH2eCOeNH2 (S D FineAR) were used. The stoichiometric amounts of the ingredientsrequire for preparation of samples were calculated by using co-efficients of multiplier in balanced chemical reaction describe inTable 1. Ingredients were thoroughly mixed in an Agate Mortar,adding little amount of double distilled water an aqueous homo-geneous solution was obtained. The aqueous solution was thentransferred in to a china basin. The China basinwas introduced in topreheated muffle furnace maintained at 550 �C. The solution boils,foams and ignites to burn with flame and obtained a voluminous,

Table 1The molar ratios of ingredients used in the synthesis and corresponding chemicalreactions.

S.N. Phosphors Corresponding reaction with balanced molar ratiosof precursors

1. Ba3Y(2-x) (BO3)4:Eu3þ

(2-x) Y(NO3)3 þ 3Ba(NO3)2 þ 4H3BO3 þ 10CO(NH2)2þ 2.5 NH4NO3 þ x Eu(NO3)3 550 �C / Ba2Y2(BO3)4:Eu3þ þ Gaseous products (H2O[, NH3[ and NO2[)(x ¼ 0.03, 0.05, 0.07)

2. Sr3Y(2-x) (BO3)4:Eu3þ

(2-x) Y(NO3)3 þ 3Sr(NO3)2 þ 4H3BO3 þ 10CO(NH2)2þ 2.5 NH4NO3 þ x Eu(NO3)3 550 �C / Sr3Y2(BO3)4:Eu3þ þ Gaseous products (H2O[, NH3[ and NO2[)(x ¼ 0.03, 0.05, 0.07)

Fig. 2. Crystal structure of M3Y2(BO3)4 (M ¼ Ba, Sr) formed by SreY and BaeYpolyhedra.

J.T. Ingle et al. / Solid State Sciences 33 (2014) 19e2420

foamy substrate. The entire combustion process was completewithin 5min. The foamy substrate crushed and grinded to obtainedfine powder which then annealed at temperature 900 �C for about2 h and suddenly cooled to room temperature to improvecrystallinity.

2.2. Characterization of samples

The X-ray diffraction (XRD) pattern of host samples ofM3Y2(BO3)4:Eu3þ(M ¼ Ba, Sr) were recorded on Rigaku MiniFlexdiffractometer with scan speed 2.000 deg/min. The morphology ofphosphor particles were studied by using Hitachi model S-4800type-2 FE-SEM & elemental analysis by Bruker EDS. UV PL and PLEmeasurements at room temperature were performed on a HitachiF-7000 spectrofluorometer equipped with a 450W Xenon lamp inthe range 200e600 nm, with spectral slit width of 2.5 nm. VUV PLspectra were measured by FLS-920T fluorescence spectrophotom-eter with a VM-504-type vacuum monochromator using a deute-rium lamp as the lighting source the emission spectra recordedunder 147 nm.

2.3. XRD and crystal structure analysis

Fig. 1 shows powder XRD of host lattice Ba3Y2(BO3)4 which isgood agreement with ICDD Card No.01-072-7110 has an ortho-rhombic structure with Pc21n space group. The structure ofBa3Y2(BO3)4 is formed by isolated BO3 triangles, bariumeoxygenpolyhedral and yttriumeoxygen polyhedral shown in Fig. 2. Thetrivalent yttrium ions occupy two different crystallographic sites(Y1 and Y2) and every Y3þ has an eight-fold coordination to form

Fig. 1. Powder XRD Pattern of host of Sr3Y2 (BO3)4 (ICDD Card No.01-073-7307).

Y2O8 polyhedra. The bond valence of Y1 is stronger than that of Y2,so the Eu3þ prefers to occupy the Y2 site. Y2O8 polyhedra columnsare built by sharing edges along the c-axis [19]. The distance be-tween two corresponding Y3þ is equal to the value of the c-parameter and the environment around Y3þ is not symmetric.While, Fig. 3 shows structural confirmation and XRD analysis ofhost lattice of Sr3Y2(BO3)4 which match with ICDD Card No.01-073-7307, the structure information of Sr3Y2(BO3)4 indicated that longerdistance between the rare-earth ions can predict to result in higherdoping concentration, and the lowered local symmetry aroundEu3þwill induce of the pure red emission results are analogs andagreed with explanation suggested by LI. Panhi et al. [20].

2.4. Particle morphology and elemental analysis

The FE-SEM micrographs of Ba3Y2(BO3)4:Eu3þand Sr3Y2(BO3)4:Eu3þ prepared under the same conditions are shown inFig. 4. The SEM images show that particles are having well definedrod like structure and rosette morphology with some agglomera-tions are observed. The average size of particles is about 1 mmsuitable for high energy VUV absorption and emission from outersurface of phosphor particles. Fig. 5 shows EDS photographs whichpredict the rare earth elements are included in sample.

Fig. 3. Powder XRD pattern of host lattice of Ba3Y2(BO3)4 (JCPDS data file .48-0307).

Fig. 4. FE-SEM micrograph of (a)Ba3Y2(BO3)4:Eu3þ(b)Sr3Y2(BO3)4:Eu3þ.

Fig. 5. EDS Photograph of (a) Ba3Y2(BO3)4:Eu3 (b) Sr3Y2(BO3)4:Eu3þ.

J.T. Ingle et al. / Solid State Sciences 33 (2014) 19e24 21

Fig. 6. UVPL Spectra Ba3Y2(BO3)4:Eu3þ (a) Excitation monitored at lem ¼ 613 nm (b)Emission at lex ¼ 254 nm.

Fig. 8. UVPL Spectra Sr3Y2(BO3)4:Eu3þ (a) Excitation monitored at lem ¼ 614 nm (b)Emission at lex ¼ 254 nm.

J.T. Ingle et al. / Solid State Sciences 33 (2014) 19e2422

3. Results & discussion

3.1. Photoluminescence of Ba3Y2(BO3)4:Eu3þ

Fig. 6 (a) and (b) shows the UV Excitation and emission spectraof Ba3Y2(BO3)4:Eu3þ.The excitation spectrummonitored for 613 nmemission mainly consists of an intense double humped broad bandpeaking at 242e248 nm corresponds to charge transfer band (CTB)of Eu-oxygen The emission spectrum under 254 nm UV excitationconsists of a sharp intense line peaking at 613 nm which corre-sponds to the 5D0 /

7F2 transition of Eu3þ indicates that the Eu3þ

ions occupies a non centro-symmetric Cs positions in theBa3Y2(BO3)4 lattice. The other weak lines 589, and 630 nm occurswhich assigned to the 5D0 /

7F1 and 5D0 /7F3 transition of Eu3þ

ions. Fig. 7 shows the emission spectrum of Ba3Y2(BO3)4:Eu3þ un-der VUV excitation of 147 nm; there are three prominent emissionpeaks between 550 and 750 nm that ascribed to the 5D0 / 7F1(w592 nm), 5D0 / 7F2 (w613 nm) and 5D0 / 7F3 (w627 nm)transitions for Eu3þ ions. It is well known that the magnetic dipoletransitions 5D0 /

7F1 are insensitive to the site symmetry, becausethey are parity-allowed. However, the 5D0 /

7F2 transition belongs

Fig. 7. VUV Emission Spectra of Ba3Y2(BO3)

to the electric dipole transition due to an admixture of oppositeparity 4fn-15d states by an odd parity crystal-field component. Inaddition, 5D0 / 7F2 transition (DJ ¼ 2) is a hypersensitive transi-tion, and the intensity can vary by orders of magnitude, dependingon the local environment. In orthorhombic phase of this host Eu3þ

is located at a low symmetry site (without inversion symmetry),which enhanced 5D0 /

7F2 transition to emit intense and pure redlight at 613 nm [15]. Other weak peaks were corresponding totransitions of 5D0 / 7Fj (j ¼ 4, 5, 6). This phosphor have CIE co-ordinates (x ¼ 0.67, y ¼ 0.31) very close to the chromaticity coor-dinate (0.67, 0.33) of the National Television Standard Committee(NTSC) for red color [22].

3.2. Photoluminescence of Sr3Y2(BO3)4:Eu3þ

UV PL of Sr3Y2(BO3)4 is depicted in Fig. 8(a) in excitation spec-trum broad band at 248 nm was observed which is due to thecharge transition(CT) band of O2�eEu3þ. This can be concluded that

4:Eu 3þ (3, 5, 7%) under lex ¼ 147 nm.

Fig. 9. VUV Emission spectra of Sr3Y2(BO3)4:Eu3þ (3, 5, 7%) under lex ¼ 147 nm.

Table 2The CIE chromaticity (x, y) of M3Y2(BO3)4(M ¼ Ba, Sr) with optimal amountsof Eu3þ Concentration.

Phosphor Color coordinates (x, y)

NTSC (x ¼ 0.670, y ¼ 0.330)(Y, Gd)BO3:Eu (x ¼ 0.632, y ¼ 0.355)Ba3Y1.95 Eu0.05(BO3)4 (x ¼ 0.670, y ¼ 0.317)Sr3Y1.95 Eu0.05(BO3)4 (x ¼ 0.670, y ¼ 0.323)

Fig. 10. CIE Chromatic point & spectral locus of x, y co-ordinate

J.T. Ingle et al. / Solid State Sciences 33 (2014) 19e24 23

the strong absorption and high quantum efficiency of Eu3þ forexcitation in the ultraviolet region. There are groups of lines be-tween 590 nm and 630 nm in the emission spectrum under 254 nmexcitation. The main peak at 614 nm is corresponding to 5D0 /

7F2of Eu3þ. The other peaks at 592 nm, 627 nm, are due to 5D0 /

7F1,5D0 / 7F3 transitions of Eu3þrespectively shown in Fig. 8(b). Theemission spectra of Sr3Y(2-x)Eux(BO3)4 under 147 nm excitation wasshown in Fig. 9.The main peak was observed at 614 nm .It is wellknown that, intensities of transitions between different J levels are

s of wavelength (a) Ba3Y2(BO3)4:Eu3þ (b) Sr3Y2(BO3)4:Eu3þ.

J.T. Ingle et al. / Solid State Sciences 33 (2014) 19e2424

dependent on local symmetry and crystal field environment aboutEu3þ [21]. In strontium yttrium borates; bond valence along Y1 andY2 are different which affect concentration of rare earth ion towardhigher level which incorporates disturbance in local symmetry andprovides an uneven ambient to Eu3þ ion which occupied noncentrosymmetric site in the crystal structure of Sr3Y2(BO3)4, in-crease the more probability of electric dipole transition of5D0 /

7F2 of Eu3þ causing line emission at 614 nm. This phosphorhave CIE coordinates (x ¼ 0.67, y ¼ 0.32) close to the chromaticitycoordinate indicated in Table 2 of (NTSC) for red color [22]. Chro-matic point is shown in Fig. 10.

3.3. Concentration quenching in Eu3þ activated Ba3Y2(BO3)4 (BYB)and Sr3Y2(BO3)4(SYB)

Figs. 7 and 9 shows the VUV emission spectra (lex ¼ 147 nm) ofphosphors with different Eu3þ concentrations. Emission peaks arelocated in the same region of spectrum with regular pattern andpositions each curve resembles except the intensity. Withincreasing Eu3þ ions concentration, the emission intensities areincrease firstly and reach a maximum at x ¼ 0.05, then decreasewith further increasing Eu3þ ions concentration (shown in inset).The excessive doping leads to concentration quenching of the Eu3þ

emission. Concentration quenching may occur because the excita-tion energy migrates among a large number of centers before beingemitted [23]. Thus the energy transfer strongly depends on thedistance between the Eu3þ ions. For this reason, it is necessary toobtain the critical distance (Rc), which is the critical separationbetween donors (activators) and acceptors (quenching site), and itcan be estimated according to the following equation:

Rc ¼ 2�

3V4pXcZ

�13

(1)

where Xc is the critical concentration, Z is the number of the Y3þ

ions in the unit cell and V is the volume of the unit cell. By takingthe experimental and analytic values of Xc, Z and V (0.05, 4,1027.07�A3 and 0.05, 4, 936.23 �A3 respectively), the critical transferdistance of Eu3þ in the Ba3Y2(BO3)4 and Sr3Y2(BO3)4 host was foundto be about 20.96 �A and 19.10 �A respectively. Moreover, concen-tration quenching usually occurs as a result of non-radiative energytransfer among luminescent centers. Non-radiative energy transferfrom one Eu3þ to another Eu3þ can be controlled by three differentmethods: radiation re absorption, exchange interaction, or electricmultipolar interaction [24]. The mechanism of radiation re ab-sorption comes into effect only when the excitation and theemission spectra have broad overlap. Thus, the small spectraoverlap for these phosphors indicates that the radiation of re ab-sorption can be ignored in this case. The exchange interactionneeds a large direct or indirect overlap between donor andacceptor, which is responsible for the energy transfer for forbidden

transitions and shorter critical distances of less than 5 �A. In Eu3þ

activated BYB, SYB phosphors the Rc is much larger than 5�A, hence,the mechanism of exchange interaction is ineffective. As a result,the process of energy transfer of Eu3þ ions in these phosphorswould be due to electric multipolar interaction.

4. Conclusion

Eu3þ activated metal yttrium borates M3Y2(BO3)4 (M ¼ Ba, Sr)(BYB) and (SYB) red phosphors were prepared by a simple, timesaving, low temperature and inexpensive solution combustiontechnique. The phosphors were effectively excited under UV, VUVradiations. Under 254 nm 147 nm both sample exhibits sharpintense line peaking at around 613 nm which corresponds to the5D0 /

7F2 transition of Eu3þ. With respect color purity issue of redemission these phosphors have CIE coordinates (x ¼ 0.67, y ¼ 0.32)close to the chromaticity coordinate (0.67, 0.33) by NTSC for redcolor could be efficiently employed in PDPs applications.

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