Lithuanian Journal of Physics article / Lietuvos fizikos žurnalo straipsnis

²⁷Al MAS NMR SPECTROSCOPY STUDY OF Eu²⁺-DOPED AND Dy³⁺-CO-DOPED SrAl₄O₇
Martynas Misevičius^a,b, Laurynas Dagys^c, Arūnas Maršalka^a, Kristina Kristinaitytė^a, and Vytautas Balevičius^a
^aInstitute of Chemical Physics, Vilnius University, Saulėtekio 3, 10257 Vilnius, Lithuania
^bInstitute of Chemistry, Vilnius University, Naugarduko 24, 03225 Vilnius, Lithuania
^cDepartment of Chemistry, University of Southampton, SO17 1BJ, Southampton, UK
Email: vytautas.balevicius@ff.vu.lt

Received 6 December 2019; accepted 16 December 2019

The Eu²⁺-doped strontium aluminate SrAl₄O₇ samples have shown the blue-green persistent luminescence at 490 nm while the co-doping with Dy³⁺ shifts the maximum of emission to 475 nm. Undoped, 3% Eu-doped and 6% Dy-co-doped SrAl₄O₇ samples were prepared by the solid state-reaction method and studied by the solid-state ²⁷Al MAS NMR applying the single pulse-acquire and Hahn-echo pulse sequences. It was shown that the Eu²⁺ with Dy³⁺ ion doping did not affect the bulk structure as well as the local Al environment in SrAl₄O₇. This means that large shifts of the emission maximum cannot be caused by changes in the local environment upon the co-doping of SrAl₄O₇:Eu²⁺ with Dy³⁺. However, the spectral features observed in the range between the signals of 4- and 6-coordinated Al (20–40 ppm) indicate that certain phase imperfections are present in all studied samples, and most probably amorphous/glassy domains were formed. Note that such amount of phase impurities was not detected by standard XRD or FTIR methods. This has revealed the ²⁷Al MAS NMR technique to be a very effective tool monitoring the phase perfectness in series of strontium aluminate samples.

Keywords: solid-state NMR, magic-angle spinning, strontium aluminate, europium, dysprosium
PACS: 61.72.Hh, 76.60-k, 82.56.-b

Eu²⁺ LEGIRUOTŲ IR Dy³⁺ KOLEGIRUOTŲ SrAl₄O₇ TYRIMAI ²⁷Al MAS BMR SPEKTROMETRIJOS METODU
Martynas Misevičius^a,b, Laurynas Dagys^c, Arūnas Maršalka^a, Kristina Kristinaitytė^a, Vytautas Balevičius^a

^aVilniaus universiteto Cheminės fizikos institutas, Vilnius, Lietuva
^bVilniaus universiteto Chemijos institutas, Vilnius, Lietuva
^cSautamptono universiteto Chemijos katedra, Sautamptonas, Jungtinė Karalystė

Eu²⁺ legiruoti stroncio aliuminatai SrAl₄O₇ pasižymi mėlynai žalia išliekančiąja liuminescencija ties 490 nm, o juos kolegiravus Dy³⁺ jonais emisijos maksimumas pasislenka link 475 nm. Kietafazių reakcijų metodu buvo paruošti nelegiruoti, 3 % Eu legiruoti ir 6 % Dy kolegiruoti SrAl₄O₇ mėginiai, kurie ištirti taikant kietojo kūno ²⁷Al MAS („magiško kampo sukimo“) BMR spektrometrijos metodą. Naudotos pavienio impulso ir Hahno sukinių aido impulsų sekos. Nustatyta, kad SrAl₄O₇ legiravimas Eu²⁺ ir Dy³⁺ jonais neturi įtakos kristalinei struktūrai visame bandinio tūryje bei lokaliai Al atomų aplinkai. Tai reiškia, kad toks pastebimas emisijos maksimumo poslinkis SrAl₄O₇:Eu²⁺ kolegiruojant Dy³⁺ nėra nulemtas lokalios kristalinės struktūros pokyčių. Kita vertus, BMR spektro dalis, stebima tarp keturių ir šešių koordinuotų Al signalų (20–40 m.d.), parodo, kad šiuose bandiniuose yra kitų fazių priemaišų, ir, labiausiai tikėtina, amorfinių / stikliškų domenų. Pažymėtina, kad tokie maži fazinių priemaišų kiekiai nebuvo aptikti įprastais ir bene dažniausiai šiam tikslui pasiekti taikomais rentgeno difrakcijos (XRD) bei Furjė vaizdavimo infraraudonosios spektrometrijos (FTIR) metodais. Tai rodo, kad ²⁷Al MAS BMR metodas gali būti labai efektyvus įrankis kontroliuojant stroncio aliuminatų serijos junginių fazinį grynumą.

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