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

用透射电子能谱观察到，直径为3 nm的ZnS：Mn^&lt；2+&gt；纳米晶表面包覆了二氧化硅，形成了20±4 nm的核/壳颗粒。对于二氧化硅修饰的ZnS：Mn^&lt；2+&gt；纳米晶，其d-d跃迁引起的光致发光强度随正硅酸乙酯含量的增加而增加，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。相反，经十二烷基磷酸酯(HLP)和二氧化硅修饰的ZnS：Mn^&Lt；2+&Gt；纳米晶的荧光强度随着TEOS用量的增加而降低。~lt；31&gt；P CP/MAS核磁共振谱表明，硅壳中断了磷酸基与ZnS：Mn^&lt；2+之间的化学作用。这些结果表明，从发光增强的角度来看，对纳米晶ZnS：Mn^&lt；2+&gt；进行HLP表面修饰比形成二氧化硅壳层更有效。将ZnS：Mn^&lt；2+&gt；/SiO_2核/壳胶体溶液老化14天，得到的粉末样品的发光强度比老化1天时提高了3倍。这可能归因于较好的量子限制效应和老化后在硫化锌中掺入更均匀的Mn~(2+)。所制备的ZnS：Mn^&lt；2+&gt；/SiO_2核/壳纳米荧光粉分散片的透过率高于块体荧光粉分散片。这归因于前者可见光的瑞利散射明显较低。由于微米级的颗粒尺寸，块状荧光粉分散的薄膜发生了Mie散射。纳米级荧光粉分散片的荧光强度随着荧光粉含量的增加而增加，而块状荧光粉分散片的荧光强度随着荧光粉含量的增加而降低。这也是由于纳米荧光粉的高透明度和橙色发射的后向散射损失可以忽略不计。

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.