Enhancement of the up-conversion luminescence from NaYF sub(4):Yb super(3+), Tb super(3+)

• Published in: Physica. B, Condensed matter Condensed matter, 2014-04, Vol.439, p.20-23
• Main Authors: Holsa, Jorma, Laihinen, Tero, Laamanen, Taneli, Lastusaari, Mika, Pihlgren, Laura, Rodrigues, Lucas CV, Soukka, Tero
• Format: Article
• Language: English
• Subjects: Condensed matter; Energy transfer; Ethyl alcohol; Fluorides; Luminescence; Stoichiometry; Upconversion; Washing
• ISSN: 0921-4526
• DOI: 10.1016/j.physb.2013.11.020

The synthesis conditions of the Yb super(3+) and Tb super(3+) co-doped NaYF sub(4) were optimized by reducing the number of washings to include only ethanol. The avoidance of the loss of amorphous NaF prior to post-annealing of the as-prepared materials resulted in the enhancement of the otherwise rather weak up-conversion from Tb super(3+) by 1-2 orders of magnitude. At the same time, the temperature of formation of the hexagonal NaRF sub(4) phase with high up-conversion could be lowered by 100 [degrees]C down to 350 [degrees]C. This improvement in up-conversion was concluded to result from the better stoichiometry of the material without washing with water. The deficit of Na super(+) would result in the excess of fluoride which, although not as fatal to the luminescence as the fluoride vacancies, has serious implications to the up-conversion intensity. A further enhancement in the up-conversion luminescence was observed to be due to the Er super(3+) ion impurity frequently associated with high-concentration Yb super(3+) materials. The mechanism involving the unintentional Er super(3+) sensitizer and the resonance energy transfer in the Yb super(3+) -Er super(3+) -Tb super(3+) co-doped NaYF sub(4) were discussed based on the energy level schemes of the Yb super(3+), Er super(3+), and Tb super(3+) ions in NaYF sub(4).