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Origin of Violet‐Blue Emission in Ti‐Doped Gahnite
Author(s) -
Dereń Przemysław J.,
Stefańska Dagmara,
Ptak Maciej,
Mączka Mirosław,
Walerczyk Wiktoria,
Banach Grzegorz
Publication year - 2014
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.12858
Subject(s) - materials science , analytical chemistry (journal) , vacancy defect , annealing (glass) , titanium , doping , spinel , grain size , absorption spectroscopy , band gap , hydrothermal circulation , crystallography , chemistry , metallurgy , physics , optoelectronics , chromatography , quantum mechanics , seismology , geology
ZnAl 2 O 4 doped with Ti 4+ (2%) was synthesized by the hydrothermal method at 220°C at pressure of 25 bars. An average grain size of the as‐prepared sample was 3 nm, the samples with biggest grain size were obtained after annealing at 300°C, 500°C, 600°C, 700°C, and 900°C, diameter of the latter was about 33 nm. IR spectroscopy indicated that ZnAl 2 O 4 was partially inverted. The degree of the inversion decreases with increase in the annealing temperature but increases with increasing Ti 4+ content. Absorption and emission spectra as well as emission decay profiles were recorded at 300 and 77 K. The observed spectra are due to charge‐transfer O 2− ↔ Ti 4+ transitions. Color of the emission depends on the nanocrystal size and with increase in its diameter changes from violet to blue, accordingly the absorption bands exhibit redshift. The calculations based on Density Functional Theory confirmed the experimental results. 3 d electrons of titanium ions form the bottom of the ZnAl 2 O 4 : Ti 4+ conduction band, oxygen, aluminum or zinc vacancies create additional levels in the gahnite energy band gap. It was also found that in ZnAl 2 O 4 aluminum or zinc vacancy induces magnetism with relatively high magnetic moment close to 1 μ B per vacancy.