Dy 3+ /Tb 3+ co-doped oxyfluoride glass ceramics (GC) containing lithium tetrafluoroyttrium (LiYF 4 ) and yttrium fluoride (YF 3 ) nanograins were prepared by a traditional melt-quenching approach. The crystalline phases and morphologies of the GCs were investigated. The GCs showed enhanced green emission from Tb 3+ ions and the quenching of Dy 3+ emission because of the efficient energy transfer from Dy 3+ to Tb 3+ ions. The electric dipole-dipole interactions were responsible for the energy transfer mechanism between Dy 3+ and Tb 3+ ions. The energy transfer efficiencies of these glass ceramics were calculated from their decay curves. The Dy 3+ /Tb 3+ co-doped oxyfluoride GCs with various visible emissions were found to be potential candidates for white-light emitting diode applications.
Bin Zhou,Bing Xu,Huimei He,Zhanjun Gu,Bing Tang,Ying Ma,Tianyou Zhai
We report the enhancement of green upconversion luminescence in tetrahedral LiYF4:Yb/Er nanoparticles by Mn2+ ion doping, which is different from the enhanced single-band red emission dominated by Mn2+ ions in cubic NaLnF4:Yb/Er (Ln = Y, Gd, Lu) nanoparticles. The energy levels of the first excited state 4T1 of Mn2+ in tetrahedral LiYF4:Gd and cubic NaGd(Y)F4 are compared by detection of emissions from Mn2+via the energy transition from Gd3+ to Mn2+ with excitation at 275 nm. The coordination environments of Mn2+ in these two host lattices have been investigated by X-ray absorption fine structure measurements. The results demonstrate that the formation of tetrahedral MnF4 in tetragonal LiYF4 arising from the replacement of Ln3+ ions with Mn2+ ions leads to a higher energy level of the Mn2+ 4T1 state than that in octahedral MnF6 in cubic NaYF4. The high-lying excited state of tetrahedral MnF4 is close to the green emitting 4S3/2 state of Er3+ and thus enhances green upconversion emission in tetragonal LiYF4:Yb/Er, while the low-lying excited state of octahedral MnF6 dominates red emission in cubic NaYF4:Yb/Er. These findings provide direct evidence for the key roles of the host lattices and more possibilities in modulating the upconversion behaviour of lanthanide-based nanoparticles by transition-metal ion doping to achieve the desired goals of specific applications.
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