The mechanism of long phosphorescence of $SrAl_{2-x}B_xO_4 (0 < x < 0.2)$ and $Sr_4Al_{14-x}B_xO_{25} (0:1 < x < 0.4)$ co-doped with $Eu^{2+}$ and $Dy^{3+}$

Nag, Abanti and Kutty, TRN (2004) The mechanism of long phosphorescence of $SrAl_{2-x}B_xO_4 (0 < x < 0.2)$ and $Sr_4Al_{14-x}B_xO_{25} (0:1 < x < 0.4)$ co-doped with $Eu^{2+}$ and $Dy^{3+}$. In: Materials Research Bulletin, 39 (3). pp. 331-342.

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Abstract

The role of $B_2O_3$ in realizing the long phosphorescence of Eu(II) + Dy(III) doped strontium aluminates has been investigated. IR and solid state $^{27}$Al MAS NMR spectra show the incorporation of boron as $BO_4$ in the $AlO_4$ framework of $SrAl_2O_4$ and $Sr_4Al_{14}O_{25}.$ Phosphor, made free of glassy phases by washing with hot acetic acid þ glycerol, did not show any photoconductivity under UV irradiation, indicating that the mechanism involving hole conduction in valence band is untenable for long phosphorescence. EPR studies confirm the presence of both electron and hole trap centers. $Dy^{3+}$ forms substitutional defect complex with borate; $[Dy–BO_4– V_{Sr}]^{2-},$ and acts as a hole trap center. The electron centers are formed by the oxygen vacancies associated with $BO_3^ {3-},$ i.e. $[BO_3–V_O]^{3-}.$ Under indigo light or near UV irradiation, the photoinduced electron centers are formed as $[BO_3–V_O(e’)]^{4-}.$ The holes are released from $[Dy–BO_4–V_{Sr}(h^\bullet)]^{1-}$ under thermal excitation at room temperature. The recombination of electrons with holes releases energy which is expended to excite $Eu^{2+}$ to induce long phosphorescence.

Item Type:	Journal Article
Publication:	Materials Research Bulletin
Publisher:	Elsevier
Additional Information:	The copyright belongs to Elsevier.
Keywords:	A. Inorganic materials;C. Infrared spectroscopy;C. Nuclear magnetic resonance (NMR);D. Electronic paramagnetic resonance (EPR);D. Luminescence
Department/Centre:	Division of Chemical Sciences > Materials Research Centre
Date Deposited:	30 May 2006
Last Modified:	19 Sep 2010 04:27
URI:	http://eprints.iisc.ac.in/id/eprint/7084

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