Characterization of hybrid nanoparticle phosphors synthesized in reverse micelle nano-reactors

通过透射电子能谱（TEM）观察到，直径为3 nm的ZnS：Mn^<2+>纳米晶体表面包覆了二氧化硅，形成了20± 4 nm的核/壳结构粒子。对于用二氧化硅修饰的ZnS：Mn^<2+>纳米晶体，由于Mn^<2+>的d-d跃迁引起的光致发光（PL）强度随着TEOS量的增加而增加，从而随着二氧化硅壳层厚度的增加而增加。这归因于表面缺陷的钝化和量子限制效应。与此相反，经十二烷基磷酸酯（HLP）和二氧化硅修饰的ZnS：Mn^<2+>纳米晶的荧光强度随着TEOS用量的增加而降低。~ 1 <31>P CP/MAS NMR光谱表明磷酸根基团与ZnS：Mn^&lt;2+&gt;之间的化学相互作用被二氧化硅壳层中断。结果表明，从荧光增强的角度看，ZnS：Mn ^&lt;2 +&gt;/SiO_2核/壳胶体溶液的表面修饰比形成SiO_2壳层更有效，ZnS：Mn^&lt;2+&gt;/SiO_2核/壳胶体溶液老化14 d后，所得粉末样品的荧光强度比老化1 d的提高了3倍。这可能是由于时效处理使Mn^&lt;2+&gt;更均匀地掺入到ZnS中，从而获得更好的量子限制效应。ZnS：Mn^2+/SiO2核/壳纳米荧光粉分散片的透光率高于ZnS：Mn^2+本体荧光粉分散片。这是由于前者明显较低的可见光瑞利散射。由于微米级的颗粒尺寸，本体磷光体分散片发生米氏散射。纳米荧光粉分散片的荧光强度随着荧光粉含量的增加而增加，而体相荧光粉分散片的荧光强度随着荧光粉含量的增加而降低。这也可以通过纳米磷光体片的高透明度和可忽略的橙子发射的背散射损失来解释。

ZnS:Mn^<2+> nanocrystals of 3nm in diameter were coated with silica to form 20±4nm core/shell particles, as observed by transmission electron spectroscopy. For ZnS:Mn^<2+> nanocrystals modified with silica, the intensity of photoluminescence (PL) due to d-d transition of Mn^<2+> increases with increasing the TEOS amount and hence the thickness of silica shell. This is attributed to the passivation of surface defects and quantum confinement effect. On the contrary, the PL intensity of ZnS:Mn^<2+> nanocrystals modified by both lauryl phosphate (HLP) and silica decreases with increasing the TEOS amount. ^<31>P CP/MAS NMR spectroscopy reveals that chemical interaction between phosphate groups and ZnS:Mn^<2+> is interrupted by silica shell. These results suggest that surface modification of HLP around ZnS:Mn^<2+> nanocrystals is more effective than the formation of silica shell from the viewpoint of PL enhancement.Aging of the of ZnS:Mn^<2+>/SiO_2 core/shell colloidal solution for 14 days increases the PL intensity of the obtained powder sample by a factor of three, as compared with that for 1 day. This is possibly attributed to the better quantum confinement effect and the more homogeneous incorporation of Mn^<2+> to ZnS by aging. The transparency of the ZnS:Mn^<2+>/SiO_2 core/shell nano-phosphor-dispersed sheet was higher than that of ZnS:Mn^<2+> bulk-phosphor- dispersed sheet. This is attributed to the markedly lower Rayleigh scattering of visible light for the former. The Mie scattering occurs for the bulk-phosphor-dispersed sheet because of the micrometer particle size. The PL intensity of the nano-phosphor-dispersed sheet increased with increasing the phosphor's content, while the PL intensity of the bulk-phosphor-dispersed sheet decreased with increasing the phosphor's content. This is also explained by the high transparency and the negligible backscattering loss of the orange emission for the nano-phosphor's sheet.