Effect of Composition and Synthesis Route on Structure and Luminescence of NaBaPO4:Eu 2+ and ZnAl2O4:Eu 3+

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1 Proc. 14th Int. Conf. on Glol Reserch nd Eduction, Inter-Acdemi 201 JJAP Conf. Proc. 4 (2016) The Jpn Society of Applied Physics Effect of Composition nd Synthesis Route on Structure nd Luminescence of NBPO4:Eu 2+ nd ZnAl2O4:Eu 3+ Vdim V. Bkhmetyev 1, Lev A. Leedev 1*, Vitlyi V. Mlygin 1, Ntly S. Podsypnin 1, Mxim M. Sychov 1, Victor V. Belyev 2 1 St. Petersurg Stte Institute of Technology (technicl university),, 26 Moskovsky Prospect, Sint-Petersurg, Russi 2 Moscow Regionl Stte University, Russi E-mil: 19lion@gmil.com (Received Octoer 13, 201) NBPO 4:Eu 2+ nd ZnAl 2O 4:Eu 3+ phosphors with different dopnt content were prepred y solution-comustion (SC) nd sol-gel (SG) method. SC route gives smples with high crystllinity, tht does not lwys leds to increse in luminescent properties due to formtion of dmixture phses. In NBPO 4 phosphor series, crystllite size reversly depends on dmixture B 3(PO 4) 2 phse content. Increse in europium concentrtion up to 10% led to decrese of crystllite size in smples prepred y SC method, ut increse of crystllite size in smples prepred y SG method. For ZnAl 2O 4:Eu 3+, prepred y sol-gel technique, increse in Eu 3+ concentrtion leds to morphiztion of structure. 1. Introduction Inorgnic phosphors re widely used in modern life in numer of different pplictions such s light sources, lsers, electronic devices, medicine etc. Phosphor s luminescent properties determines their qulity nd pplictions. Luminescence depend on numer of fctors, such s chemicl composition, crystl structure, dopnts, etc., nd cn e controlled using vrious synthetic technique nd tretments [1-4]. It is well known, tht for the efficient luminescence, especilly cthodoluminescence, crystllite size is very importnt, since oundries etween crystllites ply role of non-rditive recomintion sites [3]. Influence of synthesis temperture, time on crystllite size ws extensively studied for mny phosphors, however effect of ctivtor content on crystllite size is not well known suject [4,]. For exmple, effect of Eu 3+ concentrtion on crystl structure of Y 2O 3 phosphors, prepred y Pechini nd solution-comustion methods were descried [4,]. It ws shown tht increse of dopnt concentrtion leds to increse of crystllite size of Y 2O 3: Eu 3+ phosphor prepred y sol-gel method tht ws explined y ccelertion the phenomenon of nucletion of crystls in the presence of impurities. However it is lso known tht increse of impurities concentrtion leds to increse in numer of nucletion centers nd therefore decrese of crystllite size. In this work synthetic route influence on effect of dopnt concentrtion on crystl structure nd luminescent properties of phosphors prepred vi different synthetic methods ws studied. There were chosen sol-gel (SG) method, s one of the most well-known nd widely used synthetic route, which however consists of severl steps nd is time consuming, nd solution-comustion (SC) method, s fst nd energy efficient technique. Zinc luminte spinel nd mixed sodium-rium phosphte were used s host mteril with europium in three- nd divlent sttes s dopnt. NBPO 4:Eu 2+ phosphor is known s chemiclly stle nd promising mteril for W-LED ppliction. ZnAl 2O 4 my e used s UV emitting

2 cthode-ry phosphor for pulsed UV sources without further doption, Eu 3+ ctivtion mkes it source of red component in field emission displys or light uls. Europium ion emission is highly ffected y ion position in lttice, crystl field nd coordintion, thus it cn e used s indictor for structure nlysis [4-8]. 2. Experimentl Two types of mterils were otined y two synthetic routes tht gives four series of phosphors with different concentrtion of ctivtor in ech. All chemicls were nlyticl grde. For prepred smples X-ry diffrction (XRD) spectr were mesured using Difry X-ry diffrctometer, photoluminescence (PL) spectr on Avspec-3648 spectrofluorimeter nd rightness using IL rightness meter. 2.1 Synthesis of NBPO 4:Eu 2+ vi solution-comustion method NBPO 4:Eu 2+ phosphor ws synthesized y solution-comustion method using -lnine s fuel. The strting mterils were B(NO 3) 2, NH 2PO 4, Eu 2O 3, HNO 3, NH 4NO 3 nd -lnine. Firstly, Eu 2O 3 ws plced in thin wll qurtz eker nd dissolved in concentrted nitric cid to form nitrte solution. Then solution of B(NO 3) 2, NH 2PO 4, NH 4NO 3 nd -lnine in smll mount of distilled wter ws dded. The mount of -lnine ws douled from stoichiometric nd NH 4NO 3 ws used to increse temperture of rection. The precursor solution ws plced on hot plte to evporte wter nd form viscous mss tht self ignites nd urns producing lrge mount of gses nd forms white sponge like product. To produce NBPO 4:Eu 2+ phosphor, product ws milled in mortr nd plced in corundum ots nd introduced in tue furnce for nneling under reductive tmosphere (%H 2 + 9% N 2) t C for two hours. 2.2 Synthesis of NBPO 4:Eu 2+ vi sol-gel method Required mount of europium oxide ws plced in eker nd dissolved in 3% nitric cid on mgnetic stirrer to form nitrte solution. Brium nitrte solution ws mixed in the eker with europium nitrte nd sodium phosphte solution ws dded dropwise to form trnslucent sol. Product ws filtered nd wshed with distilled wter on Buchner funnel nd dried t С in vcuum drying cinet. The xerogel ws milled in mortr, plced in corundum crucile nd introduced in muffle furnce for two hours t C. Then reduction nneling ws done s descried ove. 2.3 Synthesis of ZnAl 2O 4:Eu 3+ vi solution-comustion method ZnO, Eu 2O 3, Al(NO 3) 3*9H 2O, HNO 3 nd ure were used s strting mterils. Oxides were plced in qurtz eker nd dissolved in concentrted nitric cid to form cler solution. Aluminum nitrte nd ure were dissolved in minimum mount of distilled wter nd dded to eker. The precursor solution ws plced on hotplte to remove wter nd then introduced in preheted furnce t C to strt rection with formtion of porous white product with fom structure. Fom ws nneled t C for two hours nd milled. 2.4 Synthesis of ZnAl 2O 4:Eu 3+ vi sol-gel method Synthesis strts from prepring nitrte solution y dissolving required mounts of europium nd zinc oxides in nitric cid in orosilicte glss eker under mgnetic stirring. Aluminum nitrte nd wt% solution of PEG-4000 were dded to resulting solution. The ZnAl 2O 4 sol ws formed cused y n ddition of mmoni solution until ph reched vlue 6-7. Product ws filtered on Buchner funnel, dried t С, milled nd nneled in furnce t C for two hours.

3 Results nd discussion 3.1 NBPO 4:Eu 2+ phosphors Figure 1 shows XRD dt of NBPO 4 smples. Using Shrer formul crystllite sizes were clculted, results re shown in the Tle I. Smples prepred using solution-comustion rout Fig. 1(), 1() nd 1(c) represents NBPO 4 with lower content of dmixture phse, in contrst to smples prepred y sol-gel method Fig. 1(d), 1(e) nd 1(f) tht contin B 3(PO 4) 2 nd B 2P 2O 7 phses. It cn e esily seen, tht crystllite size hs opposite correltion to B 3(PO 4) 2 phse content since formtion of dmixture phse prevents crystllite growth. Crystllites of smples prepred y SC method with increse of dopnt concentrtion decrese in size nd for those prepred vi SG increse in size with europium concentrtion increse up to 10%, this is similr to wht ws oserved in works [4,] for Y 2O 3 phosphors. % Eu h % Eu 1% Eu k 7% Eu c 20% Eu l 10% Eu d m 20 % Eu % Eu e 1% Eu n 7% Eu f 20% Eu o 10% Eu g NBPO B3(PO4) B2P2O p Ghnite -669 AlEuO Thet-Scle (degrees) 2-Thet-Scle (degrees) Fig. 1. XRD ptterns of NBPO 4 phosphors prepred y SC (,,c) nd SG method (d,e,f) nd ZnAl 2O 4 phosphors prepred y SC (h,k,l) nd SG method (m,n,o); (g,p)-pdf dt. Tle I. Crystll properties of mixed sodium-rium phosphte phosphors. Synthetic route Solutioncomustion Sol-gel Prmeter Europium concentrtion, % Crystllite size, nm B 3(PO 4) 2 phse content, % Crystllite size, nm B 3(PO 4) 2 phse content, %

4 Photoluminescence spectr of smples re shown on the Fig. 2, their shpe wekly depends on dopnt concentrtion ut much stronger depends on synthetic route. The given spectr were decomposed into Gussin nds. Bnds with mximums t 420, 40 nd 480 nm re the most intense ones. According to literture dt, 40 nd 480 nm nds elong to Eu 2+ in 12 (EuII) nd 10 (EuIII) coordinted sttes tht corresponds to B 2+ nd N + /B 2+ sites in NBPO 4 mtrix nd 420 nm (EuI) to Eu 2+ in B 2+ sites of B 3(PO 4) 2 mtrix [9, 10]. It cn e seen tht peks of 12- coordinted europium ions decresing with increse of doping content. Pek t 420 nm tht elongs to Eu 2+ in B 3(PO 4) 2 hs no correltion to europium concentrtion, tht cn e cused y nonuniform distriution of dopnt etween phses. For sodium-rium phosphte phosphor series, europium concentrtion vries from to 20%. Fig. 3 shows rightness depending on Eu 2+ content, it cn e esily seen, tht optimum concentrtion does not depend on synthesis rout nd correspond to 10%, however smples prepred y solution-comustion method righter then those mde y sol-gel due to presence of dmixture phses, since luminescence of B 3(PO 4) 2:Eu 2+ is in shorter wvelength region thn those of NBPO EuI EuII EuIII EuI EuII EuIII Wvelength (nm) Wvelength (nm) Fig. 2. Photoluminescence spectr of NBPO 4 sed phosphors prepred y solution-comustion () nd sol-gel method () with 1 % Eu 2+ concentrtion. Brightness [.u.] NBPO4 Brightness [.u.] ZnAl2O Eu concentrtion [%] Eu concentrtion [%] Fig. 3. Brightness depending on Eu content in NBPO 4 nd ZnAl 2O 4 phosphors prepred y solutioncomustion () nd sol-gel method (). 3.2 ZnAl 2O 4:Eu 3+ phosphors Zinc luminte spinel XRD ptterns re shown on the Fig. 1, ccording to them ZnAl 2O 4:Eu 3+ phosphors produced y sol-gel route, hve stronger influence of Eu 3+ ions concentrtion on crystl structure. Nmely, increse of europium concentrtion leds to morphiztion, tht cn ee seen in rodening of XRD peks, with incresing of doping level. Smples prepred y solution-

5 comustion method hve higher crystllinity, due to high rection temperture, it cn e seen y nrrow peks on XRD ptterns. Using Shrer formul crystllite sizes were clculted, Tle II, it cn e seen tht increse in dopnt concentrtion leds to chnge in crystllite size tht hs different tendency depending on synthetic rout, similr ehvior for Y 2O 3:Eu 3+ phosphor ws oserved in our previous work [4] nd lso descried ove for NBPO 4. Europium ions my sustitute Zn 2+ or Al 3+ sites in spinel mtrix or locte on surfces of nnoprticles due to their porosity. Becuse of Eu 3+ ions rdii (0.9 Å) noticely lrger thn tht of Zn 2+ (0.68 Å) or Al 3+ (0.4 Å), surfce locliztion is more prole. Tle II. Synthetic route Solutioncomustion Sol-gel Crystll properties of ZnAl 2O 4 phosphors. Prmeter Europium concentrtion, % 7 10 Crystllite size, nm EuAlO 3 phse content, % Crystllite size, nm EuAlO 3 phse content, % <1 <1 <1 From luminescence spectr shown on the Fig. 4 it cn e seen tht 620 pek is the most intense for sol-gel prepred smples, it corresponds to D 0 7 F 2 electric-dipole trnsition of Eu 3+ nd is sensitive to the site symmetry, it is llowed when europium ions occupies sites without n inversion symmetry [11]. Due to morphous mtrix Eu 3+ ions occupies low symmetry sites tht intensifies nd t 620 nm, therey it confirms XRD dt tht increse of Eu 3+ concentrtion results in decrese of crystllite size nd morphiztion tht is similr to YAG smples descried in [4] nd it is importnt tht ZnAl 2O 4 nd Y 3Al O 12 my e clssified s doule oxide system. However, for smples prepred y SC, europium concentrtion does not noticely ffect crystllinity, tht lso shown y low intensity of 620 nm pek nd intense 610 nm pek tht elongs to D 0 7 F 1 mgnetdipole trnsition tht is low sensitive to symmetry. D0 7 F1 D0 7 F D0 7 F D0 7 F Wvelength (nm) Wvelength (nm) Fig. 4. Photoluminescence spectr of ZnAl 2O 4 sed phosphors prepred y solution-comustion () nd solgel method () with 7 % Eu 2+ concentrtion. Figure 3 shows rightness depending on Eu 3+ content, it cn e seen tht smples prepred y SG hs higher rightness then SC prepred, even thou the former one hs lower crystllinity. Tht cn e explined y presence of EuAlO 3 perovskite phse Fig. 1(h), 1(k) nd 1(l), tht s formed in smples prepred y SC route n its content increses proportionlly to europium concentrtion, this results in europium ion consumption, so there is smll mount of luminescent centers left in the spinel mtrix. The presence of the perovskite phse in SC smples cn e explined y the highly non-equilirium conditions of process due to short rection time nd lrge exothermic effect.

6 On the other hnd, SG process occurs t low speed in solvent medium tht provides conditions close to equilirium in tht cse the formtion of solid solution is more likely. 3. Conclusion NBPO 4:Eu 2+ nd ZnAl 2O 4:Eu 3+ phosphors with different dopnt content were prepred y solution-comustion nd sol-gel method. Solution-comustion route gives smples with higher crystllinity, which does not lwys leds to increse of luminescent properties due to formtion of dmixture phses. In NBPO 4 phosphor series, crystllite size reversely depends on dmixture B 3(PO 4) 2 phse content. Below 10% increse in europium concentrtion led to decrese of crystllite size in smples prepred y SC method, ut increse of crystllite size in smples prepred y SG method. For ZnAl 2O 4:Eu 3+, prepred y sol-gel technique, increse in Eu 3+ concentrtion leds to morphiztion of structure, sme effect oserved in YAG smples, moreover this two host mterils cn e clssified s doule oxide systems. For ZnAl 2O 4:Eu 3+ prepred y SC increse in Eu concentrtion does not significntly ffect crystllinity nd leds to formtion of dmixture EuAlO 3 phse tht results in lower rightness. Thus doping llow to control crystllite size, tht is importnt in phosphor, cermic, nd electronics technologies. Acknowledgment This work ws supported y Ministry of Eduction nd Science of the Russin Federtion (Agreement , identifier RFMEFI7414X0002). References [1] Sychov M.M., Ogurtsov K.A., Leedev V.T., Kulvelis Yu.V., Török Gy., Sokolov A.E., V.A. Trunov, Bkhmetyev V.V., Kotomin A.A., Dushenok S.A., Kozlov A.S., Semiconductors Vol. 46, No., 2012, pp [2] Tsvetkov, M N; Chernovets, B V; Itkinson, G V; Korskov, V G; Sychev, M M., Journl of Opticl Technology, Vol. 78 Issue , pp [3] Sychov M.M., Nknishi Y., Kominmi H., Htnk Y., Hr K., Jp. J. of Appl. Phys.. Vol. 47, No. 9, 2008, pp [4] Bkhmetyev V.V., Leedev L.A., Vlsenko A.B., Bogdnov S.P., Sovestnov A.E., Minkov T.S., Minkov L.Yu., Sychov M.M., Key Engineering Mterils. Vol pp [] T.A. Pomelov, V.V. Bkovec, I.V. Korolkov, O.V. Antonov, I.P. Dolgovesov, Physics of Solid Stte, Vol. 6 issue , pp [6] Sun Jiyue, Zhng Xingyn, Du Hiyn, Journl of Rre Erths, Vol. 30, No. 2, 2012, pp [7] W. Strek, P. Deren, A. Bednrkiewicz, M. Zwdzki, J. Wrzyszcz, Journl of Alloys nd Compounds Vol , pp [8] Xing Ying Chen, Cho M, Shi Ping Bo, Zho Li, Journl of Colloid nd Interfce Science Vol , pp [9] Yong Go, Chun-Shd Shi, Chinese Journl of Chemistry Vol. 14 No. 1996, pp [10] Suyin Zhng, Ynlin Hung, Yosuke Nki, Tiju Tsuoi, Hyo Jin Seo, J. Am. Cerm. Soc., 94 [9] (2011), pp [11] Chong Peng, Guogng Li, Dongling Geng, Mengmeng Shng, Zhiyo Hou, Jun Lin, Mterils Reserch Bulletin Vol , pp