Chemical control of the photoluminescent properties of up-converting phosphors

Rebollo Pedruelo, Maria del Puy (2007). Chemical control of the photoluminescent properties of up-converting phosphors. PhD thesis The Open University.



Up-conversion luminescence of Er3+ based phosphors was studied in the following host lattices: Y2O3, GCI2O3, Gd2-xYxO3, and YVO4, with a view to developing an understanding of how emission can be tailored by manipulating the local chemical environment of the activator ion.

Laser induced luminescence measurements of Y203:Er phosphors showed evidence of Stokes and Anti-Stokes emission bands arising from excited levels under 632.8 nm radiation. Emission from 4F7/2—> 4I15/2 transitions were found to be weaker in Gd203 phosphors and were not detected in YVO4 hosts. Relative intensity of Stokes / Anti-Stokes radiation were studied as a function of the host lattice, and variations found as a consequence of crystal field changes in the activator environment.

This work was extended to an investigation of the effect of co-dopants. Low levels of Yb3+ used as sensitizer, enhanced luminescence from 4F7/2—> 4I15/2 and 4F9/2—► 4I15/2 transitions, and a novel relaxation mechanism involving energy transfer from excited states is proposed to account for the variation observed in the intensity of the emission bands. Eu3+ used as co-dopant produced energy loss due to resonant energy transfer. This phenomenon was demonstrated by undertaking thermal studies on YV04:Er,Eu co-doped phosphors. Enhancement of 4H11/2 transitions from Er3+ ions in S6 symmetry sites was observed together with 4F7/2—> 4I15/2 transition activation with increasing Eu3+ concentration.

With a view to producing phosphor powders suitable for device application, wet chemical routes were investigated in order to prepare the materials studied in this work. The synthetic approaches studied were urea co-precipitation and combustion synthesis, the reaction conditions were carefully manipulated in order to optimise the composition and morphology of the product. Spherical uniform particles in the 300 - 600 nm range were routinely prepared.

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