Department of Organic Chemistry, Faculty of Chemistry, Universidad Complutense de Madrid, 28040 Madrid, Spain.
ACS Appl Mater Interfaces. 2011 Oct;3(10):3846-54. doi: 10.1021/am2010509. Epub 2011 Oct 10.
Two new methods for covalent functionalization of GaN based on plasma activation of its surface are presented. Both of them allow attachment of sulfonated luminescent ruthenium(II) indicator dyes to the p- and n-type semiconductor as well as to the surface of nonencapsulated chips of GaN light-emitting diodes (blue LEDs). X-ray photoelectron spectroscopy analysis of the functionalized semiconductor confirms the formation of covalent bonds between the GaN surface and the dye. Confocal fluorescence microscopy with single-photon-timing (SPT) detection has been used for characterization of the functionalized surfaces and LED chips. While the ruthenium complex attached to p-GaN under an oxygen-free atmosphere gives significantly long mean emission lifetimes for the indicator dye (ca. 2000 ns), the n-GaN-functionalized surfaces display surprisingly low values (600 ns), suggesting the occurrence of a quenching process. A photoinduced electron injection from the dye to the semiconductor conduction band, followed by a fast back electron transfer, is proposed to be responsible for the excited ruthenium dye deactivation. This process invalidates the use of the n-GaN/dye system for sensing applications. However, for p-GaN/dye materials, the luminescence decay accelerates in the presence of O(2). The moderate sensitivity is attributed to the fact that only a monolayer of indicator dye is anchored to the semiconductor surface but serves as a demonstrator device. Moreover, the luminescence decays of the functionalized LED chip measured with excitation of either an external (laser) source or the underlying LED emission (from p-GaN/InGaN quantum wells) yield the same mean luminescence lifetime. These results pave the way for using advanced LEDs to develop integrateable optochemical microsensors for gas analysis.
提出了两种基于 GaN 表面等离子体激活的共价功能化新方法。这两种方法都可以将磺酸基发光钌(II)指示剂染料附着到 p 型和 n 型半导体以及未封装的 GaN 发光二极管（蓝色 LED）芯片表面。功能化半导体的 X 光电子能谱分析证实了 GaN 表面与染料之间形成了共价键。具有单光子定时（SPT）检测的共焦荧光显微镜已用于功能化表面和 LED 芯片的表征。虽然在无氧气氛下将钌配合物附着到 p-GaN 上会使指示剂染料的平均发射寿命显着延长（约 2000 ns），但 n-GaN 功能化表面显示出出乎意料的低值（600 ns），表明发生了猝灭过程。从染料到半导体导带的光致电子注入，随后是快速的反向电子转移，被认为是激发的钌染料失活的原因。这个过程使得 n-GaN/染料系统无法用于传感应用。然而，对于 p-GaN/染料材料，在存在 O(2)的情况下，荧光衰减会加速。适度的灵敏度归因于只有单层指示剂染料锚定在半导体表面上，但作为演示设备。此外，用外部（激光）源或底层 LED 发射（来自 p-GaN/InGaN 量子阱）激发测量的功能化 LED 芯片的荧光衰减产生相同的平均荧光寿命。这些结果为使用先进的 LED 开发可集成的光电化学微传感器用于气体分析铺平了道路。
