SrAl 12 O 19 :Pr 3+ nanodisks and nanoplates: New processing technique and photon cascade emission Zhaogang Nie Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China; and BK21 Physics Program and Department of Physics, Chungbuk National University, Cheongju 361-763, Korea Jiahua Zhang a) and Xia Zhang Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China Ki-Soo Lim b) BK21 Physics Program and Department of Physics, Chungbuk National University, Cheongju 361-763, Korea (Received 27 October 2008; accepted 13 January 2009) High-quality SrAl 12 O 19 :Pr 3+ nanodisks and nanoplates were fabricated via a new processing technique based on a modified polymer steric entrapment method. Serious agglomeration and large particle size distribution of final products, which usually occurred in the conventional method, were eliminated completely. The effects of new synthetic processes on the morphology, crystallization, and yield of products and the relevant mechanisms were discussed. As far as we know, SrAl 12 O 19 :Pr 3+ nanodisks with mean diameter 60 nm and thickness between 5 and 10 nm were successfully synthesized for the first time by this low-cost technique. The new synthetic method may provide a general route to synthesize other refractory mixed-oxide nanocrystals. Photon cascade emission involving transitions 1 S 0 – 1 I 6 followed by 3 P 0 – 3 H 4 in SrAl 12 O 19 :1% Pr 3+ nanodisks was investigated. Size-effect-induced blue shift of the 4f 5d states of Pr 3+ was observed in SrAl 12 O 19 :1% Pr 3+ nanodisks, in which the quantum efficiency was preserved, as in the bulk counterparts. I. INTRODUCTION Rare earth doped oxide nanocrystalline phosphors at- tract considerable attention because of their potential application in lighting and display. With the progress of nanoscience, people are now equipped with various fab- rication methods with novel properties on the nanoscale level. These so-called “size-dependent properties” are of great interest and significance. However, the processing methods necessary to produce high-crystallization phos- phor, which usually helps to achieve high luminous effi- ciency, generally involve processing at high temperature, which tends to agglomerate the primary crystallites and thus lose the possible benefits of the nanosize materials. Furthermore, the quantum efficiency (QE) of oxide phosphors fabricated in nanosize regime is usually much lower than their microsize counterparts due to surface effects. They are always assumed as the main hindrances to their practical applications. 1–5 Thus, much attention should be paid to developing more new methods to control the morphology of the nanoparticles and preserve their QEs. Some refractory mixed oxides, such as SrAl 12 O 19 (SAO; melting point > 1800  C) or other strontium aluminates, have significant technological importance because of their unique combination of mechanical, ther- mal, and optical properties, making them candidates for industries of lighting and displays, 6 laser, 7,8 cement, and even steel. 9,10 Despite their importance, the research about their synthesis is still scarce compared with other materials, such as metals and semiconductors, because they are high-temperature phase species that are very difficult to prepare and get in control. 11–14 Recently, a polymer steric entrapment (PSE, or other similar names) method using polyvinyl alcohol (PVA) or other long- chain polymer as organic carrier was developed to fabri- cate various multioxide ceramics, but usually not suit- able for synthesis of well-dispersed nanocrystals. 15–22 Herein, this method was modified, and high-quality SAO:Pr 3+ nanodisks and nanoplates were fabricated by this low-cost technique. Large particle sizes, wide parti- cle size distribution, and the phenomenon of agglomera- tion of final products, which usually occurred in conventional the PSE method, 15–22 and some other Address all correspondence to these authors. a) e-mail: zhangjh@ciomp.ac.cn b) e-mail: kslim@chungbuk.ac.kr DOI: 10.1557/JMR.2009.0193 J. Mater. Res., Vol. 24, No. 5, May 2009 © 2009 Materials Research Society 1771