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

通过透射电子能谱分析，将直径为3nm的ZnS:Mn^<2+>纳米晶体包被二氧化硅，形成20±4nm的核壳颗粒。对于用二氧化硅修饰的ZnS:Mn^<2+>纳米晶体，Mn^<2+>的d-d跃迁引起的光致发光强度（PL）随着TEOS用量的增加而增加，从而随着二氧化硅壳厚度的增加而增加。这主要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（HLP）和二氧化硅改性的ZnS:Mn^<2+>纳米晶的发光强度随着TEOS用量的增加而降低。P CP/MAS NMR谱显示，磷酸基与ZnS:Mn^<2+>之间的化学相互作用被二氧化硅壳打断。这些结果表明，从PL增强的角度来看，HLP在ZnS:Mn^<2+>纳米晶体周围的表面改性比形成二氧化硅壳更有效。ZnS:Mn^<2+>/SiO_2核/壳胶溶液时效14天后，所得粉末样品的PL强度比时效1天后提高了3倍。这可能归因于更好的量子约束效应和Mn^<2+>通过时效更均匀地掺入ZnS。ZnS:Mn^<2+>/SiO_2核/壳纳米磷分散片的透明度高于ZnS:Mn^<2+>体磷分散片的透明度。这是由于前者可见光的瑞利散射明显较低。由于颗粒尺寸为微米级，体磷分散片材发生米氏散射。纳米磷分散片的发光强度随荧光粉含量的增加而增加，体磷分散片的发光强度随荧光粉含量的增加而降低。这也可以用纳米荧光粉片的高透明度和可忽略不计的橙色发射的后向散射损失来解释。

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.