论文标题
基于灯笼的纳米晶体中状态的声子密度
Phonon density of states in lanthanide-based nanocrystals
论文作者
论文摘要
我们报告了一项对纳米和微晶灯笼状态的声子密度的混合非弹性中子和X射线散射研究，基于lanthanide的材料nay $ _ {0.8} $ yb $ _ {0.18} $ _ {0.18} $ nagd $ _ {0.8} $ yb $ _ {0.18} $ er $ _ {0.02} $ f $ _4 $。虽然大（20 nm）纳米晶体显示与微晶的振动光谱相同，但我们在低能量处发现了增强的状态声子密度，$ e \ e \ leq 15 \，\ rm {mev} $，在Ultra-S-M-S-Mall（5 nm）中nagd $ _ {0.8} $ yb $ _ {0.18} $ er $ _ {0.02} $ f $ _4 $ nanocrystals，我们分配给表面声子模式的相对光谱重量增加。基于我们对超小纳米晶体的观察，我们合理地认为，由于表面声子而导致的大纳米晶体中状态的声子密度的增加太小，无法在当前测量中观察到。本报告中描述的实验方法构成了迈向尺寸影响对上转换纳米晶体的绝对上转换量子产率的修改的第一步。
We report a combined inelastic neutron and X-ray scattering study of the phonon density of states of the nano- and microcrystalline lanthanide-based materials NaY$_{0.8}$Yb$_{0.18}$Er$_{0.02}$F$_4$ and NaGd$_{0.8}$Yb$_{0.18}$Er$_{0.02}$F$_4$. While large (20 nm) nanocrystals display the same vibrational spectra as their microcrystalline counterparts, we find an enhanced phonon density of states at low energies, $E \leq 15\,\rm{meV}$, in ultra-small (5 nm) NaGd$_{0.8}$Yb$_{0.18}$Er$_{0.02}$F$_4$ nanocrystals which we assign to an increased relative spectral weight of surface phonon modes. Based on our observations for ultra-small nanocrystals, we rationalize that an increase of the phonon density of states in large nanocrystals due to surface phonons is too small to be observed in the current measurements. The experimental approach described in this report constitutes the first step toward the rationalization of size effects on the modification of the absolute upconversion quantum yield of upconverting nanocrystals.
