Jung Taeyoung, Jo Hong Li, Nam Sang Hwan, Yoo Byeongjun, Cho Youngho, Kim Jongwoo, Kim Hyung Min, Hyeon Taeghwan, Suh Yung Doug, Lee Hohjai, Lee Kang Taek
Department of Chemistry, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, Korea.
Phys Chem Chem Phys. 2015 May 28;17(20):13201-5. doi: 10.1039/c5cp01634g.
Lanthanide-doped upconverting nanoparticles (UCNPs, NaYF4:Yb(3+),Er(3+)) are well known for emitting visible photons upon absorption of two or more near-infrared (NIR) photons through energy transfer from the sensitizer (Yb(3+)) to the activator (Er(3+)). Of the visible emission bands (two green and one red band), it has been suggested that the red emission results from two competing upconversion pathways where the non-radiative relaxation occurs after the second energy transfer (pathway A, (4)I15/2 → (4)I11/2 → (4)F7/2 → (2)H11/2 → (4)S3/2 → (4)F9/2 → (4)I15/2) or between the first and the second energy transfer (pathway B, (4)I15/2 → (4)I11/2 → (4)I13/2 → (4)F9/2 → (4)I15/2). However, there has been no clear evidence or thorough analysis of the partitioning between the two pathways. We examined the spectra, power dependence, and time profiles of UCNP emission at either 980 nm or 488 nm excitation, to address which pathway is preferred. It turned out that the pathway B is predominant for the red emission over a wide range of excitation powers.
镧系掺杂上转换纳米粒子（UCNPs，NaYF4:Yb(3+)，Er(3+)）因通过从敏化剂（Yb(3+)）到激活剂（Er(3+)）的能量转移吸收两个或更多近红外（NIR）光子后发射可见光子而闻名。在可见发射带（两个绿色带和一个红色带）中，有人提出红色发射源于两条相互竞争的上转换途径，其中非辐射弛豫发生在第二次能量转移之后（途径A，(4)I15/2 → (4)I11/2 → (4)F7/2 → (2)H11/2 → (4)S3/2 → (4)F9/2 → (4)I15/2）或在第一次和第二次能量转移之间（途径B，(4)I15/2 → (4)I11/2 → (4)I13/2 → (4)F9/2 → (4)I15/2）。然而，对于这两条途径之间的分配，尚无明确证据或深入分析。我们研究了在980 nm或488 nm激发下UCNP发射的光谱、功率依赖性和时间分布，以确定哪种途径更受青睐。结果表明，在很宽的激发功率范围内，途径B在红色发射中占主导地位。
