Zavala-Sanchez Luz A, Hirata Gustavo A, Novitskaya Ekaterina, Karandikar Keyur, Herrera Manuel, Graeve Olivia A
Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Km 107 Carretera Tijuana-Ensenada, Ensenada, Baja California C.P. 22800, Mexico.
Department of Mechanical and Aerospace Engineering, University of California, San Diego, 9500 Gilman Drive, MC 0411, La Jolla, California 92093-0411, United States.
ACS Biomater Sci Eng. 2015 Dec 14;1(12):1306-1313. doi: 10.1021/acsbiomaterials.5b00378. Epub 2015 Nov 20.
We present a cathodoluminescence study of the spatial distribution of Eu and Eu dopants in hydroxyapatite powders. The results demonstrate that the distribution of europium ions in the hydroxyapatite lattice depends on their valence state. Monochromatic cathodoluminescence images from prismatic powders show that although the Eu is distributed homogeneously in the entire powder volume, the Eu is present mainly at the powder edges. The luminescence spectrum of the Eu ions displayed a wide and strong blue emission centered at 420 nm, while the luminescence spectrum of the Eu ions displayed several orange-red emissions covering the range from 575 to 725 nm. These emissions correspond to transitions between levels 4f5d-4f (S) of the Eu ions and D-F levels of the Eu ions. Micro Raman measurements reveal that europium doping generates two phonon signals with frequencies of 555 and 660 cm, both of which have not been reported earlier. The powders were synthesized by the combustion synthesis method, maintaining constant the concentration of the europium salt used, and varying the pH of the precursor solutions to modify the concentration ratio of Eu with respect to Eu. X-ray photoelectron spectroscopy measurements were used to determine values of 0.32 and 0.55 for the ratio Eu/Eu in samples synthesized at pH values of 6 and 4, respectively. Thermal treatments of the samples, at 873 K in an oxygen atmosphere, resulted in a strong quenching of the Eu luminescence due to oxidation of the Eu ions into Eu, as well as probable elimination of calcium vacancy defects by annealing.
我们展示了对羟基磷灰石粉末中铕（Eu）和铕掺杂剂空间分布的阴极发光研究。结果表明，铕离子在羟基磷灰石晶格中的分布取决于它们的价态。来自棱柱形粉末的单色阴极发光图像显示，尽管铕在整个粉末体积中均匀分布，但铕主要存在于粉末边缘。Eu离子的发光光谱显示出以420nm为中心的宽且强的蓝色发射，而Eu离子的发光光谱显示出覆盖575至725nm范围的几种橙红色发射。这些发射对应于Eu离子的4f5d - 4f（S）能级与Eu离子的D - F能级之间的跃迁。显微拉曼测量表明，铕掺杂产生了频率为555和660cm的两个声子信号，这两个信号此前均未被报道。通过燃烧合成法合成粉末，保持所用铕盐浓度恒定，并改变前驱体溶液的pH值以改变Eu相对于Eu的浓度比。利用X射线光电子能谱测量分别确定了在pH值为6和4时合成的样品中Eu/Eu比的值为0.32和0.55。在氧气气氛中于873K对样品进行热处理，由于Eu离子氧化成Eu以及可能通过退火消除钙空位缺陷，导致Eu发光强烈猝灭。
