Y_2O_2S∶Er,Yb纳米晶的制备及其上转换和下转换发光

The preparation and the up and down-conversion luminescence of Y_2O_2S∶Er,Yb nanocrystals

采用共沉淀法,结合固-气硫化工艺制备了平均粒径约40nm的类球形Y2O2S∶Er,Yb纳米晶,并对其在980nm红外激发下的上转换和下转换发射进行了较为详细的研究。Er3+的上转换特征发射分别位于530、550和660nm附近。在表面吸附OH-和CO32-所形成的特殊声子环境下,Er3+的4S3/2→4F9/2和4I11/2→4I13/2多声子弛豫显著提高了4F9/2能级的粒子布居,致使纳米晶具有很强的660nm红光发射。并且红绿光荧光分支比会随Yb3+浓度的提高而显著增大。首次报导了Y2O2S纳米晶中Er3+的红外特征发射。源于Er3+离子4I13/2→4I15/2辐射跃迁的较强红外发射,在晶场作用下分化为峰位分别位于1501、1534和1577nm的3个发射峰。由于4I13/2能级是660nm红光发射的主要布居能级之一,该红外发射与红光发射存在明显竞争。但在较高Yb3+掺杂浓度下,高效的Yb3+→Er3+能量传递可有效削弱红外发射的竞争作用。

The near-spherical YzO2S ： Er^3＋, Yb^3＋ nanocrystals （NCs） were prepared by coprecipitation method followed by a solid-gas sulfuration technic. The average Particle size was 40nm. Under the excitation of 980nm laser diode （LD）, the up- and down-conversion luminescence was investigated. The up-conversion character emission peaks of Er^3＋ in Y2O2S nanocrystals are located at 530,550 and 660nm, respectively. Under the special phonon condition formed by surficial adsorbent OH- and CO3^2-, the 4 S3/2→4 F9/3 and 4 I11/2→4I13/3 multiphoton relaxations of Er^3＋ remarkably improves the population of 4 F9/3 level, which makes the Y3O2 S ： Er, Yb nanocrystal shows a strong red emission at 660nm. Moreover, the intensity radio of red to green emission was greatly increased with the increase in Yb^3＋ doping concentration. In addition,the inferred （IR） character emission of Er^3＋ in Y2O2S nanocrystals was reported for the first time. The stronger IR emission arising from the 4I13/2→4I15/3 radiative transition of Er^3＋ is divided into three peaks under the effect of crystal field, and the peak positions of which are located at 1501,1534 and 1577nm,respectively. Since 4I13/2 level is one of the major population levels of 660nm red emission, there is strong competition function between the IR and red emissions. However, under higher Yb^3＋ doping concentration, the highly-efficient Yb^3＋ →Er^3＋ energy transfer can effectively weaken the competition function of IR emission.