Efficient Photoluminescence of Mn2+-Doped ZnS Quantum Dots Excited by Two-Photon Absorption in Near-Infrared Window II

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• 作者：Radhu Subha ; Venkatram Nalla ; Jung Ho Yu ; Samuel Woojoo Jun ; Kwangsoo Shin ; Taeghwan Hyeon ; C. Vijayan ; Wei Ji
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：October 10, 2013
• 年：2013
• 卷：117
• 期：40
• 页码：20905-20911
• 全文大小：428K
• 年卷期：v.117,no.40(October 10, 2013)
• ISSN：1932-7455

文摘

Highly fluorescing biological labels with excitation in near-infrared window II have attracted the interest of scientific community as they are capable of increasing both penetration depth and imaging quality. However, studies on the utilization of quantum dots (QDs) in biological imaging appear to be rather limited to the near-infrared window I (NIR-I: 650鈥?50 nm). We herein report on the observation of efficient photoluminescence (PL) in Mn²⁺-doped ZnS QDs excited by two-photon absorption (2PA) in near-infrared window II (NIR-II: 1000鈥?350 nm). Multiphoton-absorption-induced PL measurements indicate that these biocompatible QDs exhibit a two-photon action cross-section of 265 GM at 1180 nm, the highest value reported to date among conventional fluorescent probes on excitation in NIR-II. This value is 1鈥? orders of magnitude higher than that for organic dye molecules excited by NIR-I photons and 3鈥? times greater than that of fluorescent proteins excited in the NIR-II. The underlying NIR-II excitation mechanism for the Mn²⁺ emission at 586 nm on account of the ⁴T₁鈥?sup>6A₁ transition is attributed to the transitions from the valence subband of ZnS QDs (or ground states of Mn²⁺ ions) to the excited states of Mn²⁺ ions by direct two-photon absorption. Transient PL measurements reveal single exponential decay with a PL lifetime of 0.35 卤 0.03 ms irrespective of excitation wavelength, which are 4鈥? orders longer than that of conventional fluorescent probes. With the excitation in NIR-II window and the unique combination of photophysical properties such as a greater two-photon action cross-section, a longer PL lifetime, and larger anti-Stokes shift (450 nm or more), Mn²⁺-doped ZnS QDs appear to be a promising candidate for deep tissue imaging applications.