Temperature-dependent photoluminescence properties of Mn-doped ZnSe quantum dots
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摘要: 量子点(QD)照明器件中电流导致的焦耳热会使其工作温度高于室温,因此研究量子点的发光热稳定性十分重要。本文利用稳态光谱和时间分辨光谱研究了具有不同壳层厚度的Mn掺杂ZnSe(Mn: ZnSe)量子点的变温发光性质,温度范围是80～500 K。实验结果表明,厚壳层(6.5单层(MLs))Mn: ZnSe量子点的发光热稳定性要优于薄壳层(2.6 MLs)的量子点。从80 K升温到400 K的过程中,厚壳层Mn: ZnSe量子点的发光几乎没有发生热猝灭,发光量子效率在400 K高温下依然可以达到60%。通过对比Mn: ZnSe量子点的变温发光强度与荧光寿命,对Mn: ZnSe量子点发光热猝灭机制进行了讨论。最后,为了研究Mn: ZnSe量子点的发光热猝灭是否为本征猝灭,对具有不同壳层厚度的Mn: ZnSe量子点进行了加热-冷却循环(300-500-300 K)测试,发现厚壳层的Mn: ZnSe量子点的发光在循环中基本可逆。因此,Mn: ZnSe量子点可以适用于照明器件,即使器件中会出现不可避免的较强热效应。Abstract: Thermal stability of quantum dot(QD) luminescence is considered as an important factor for their applications in luminescent devices because of the Joule heat caused by inevitable current. The temperature-dependent photoluminescence(PL) properties of Mn-doped ZnSe(Mn: ZnSe) QDs with different shell thickness in the temperature range from 80 to 500 K were studied by steady-state and time-resolved PL spectra. It was found that the Mn: ZnSe QDs with thick shell(6.5 monolayers(MLs)) exhibited better PL thermal stability than the thin shell coated ones(2.6 MLs). Because almost no PL quenching occurred for thick shell-coated Mn-doped QDs from 80 to 400 K, their PL quantum yield(QY) could keep 60% even at 400 K. Moreover, based on the change in temperature-dependent PL intensities and lifetimes of Mn: ZnSe QDs, the thermal quenching mechanism was proposed. Finally, the stability of Mn: ZnSe QDs with different shell thickness are discussed on the basis of heating-cooling cycling examination(300-500-300 K). For Mn: ZnSe QDs with thick shell, the PL was nearly totally recovered after the cycling examination. Thus, Mn: ZnSe QDs are promising for applications in luminescent devices, where strong thermal effect is inevitable.
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Key words:
- quantum dots /
- nanocrystal /
- Mn-doped quantum dots /
- luminescence property /
- thermal quenching
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图 1 壳层厚度分别为2.6 MLs(a)和6.5 MLs(b)的Mn∶ZnSe量子点的变温光谱，温度范围为80~500 K，激发波长为356 nm，插图中给出的是相应的量子点电镜照片
Figure 1. Temperature-dependent PL spectra of Mn∶ZnSe(2.6 MLs)(a) and Mn∶ZnSe(6.5 MLs)(b) QDs from 80 to 500 K,under excitation at 365 nm. The inset shows the typical TEM image of the QDs
图 2 Mn∶ZnSe量子点的温度依赖的发光峰能量(a)和发光半高宽(b)，实线为拟合曲线
Figure 2. Temperature-dependent PL peak energy(a) and FWHM(b) of Mn∶ZnSe QDs. Solid lines represent the fitting curves
图 3 壳层厚度分别为2.6 MLs(a)和6.5 MLs(b)的Mn∶ZnSe量子点的温度依赖荧光衰减曲线，激发波长为365 nm
Figure 3. Temperature-dependent PL decay curves of Mn∶ZnSe(2.6 MLs)(a) and Mn∶ZnSe(6.5 MLs)(b) QDs under excitation at 365 nm
图 4 壳层厚度分别为2.6 MLs(a)和6.5 MLs(b)的Mn∶ZnSe量子点的发光积分强度(方块)与荧光寿命(圆环)随温度的变化曲线，其中发光积分强度在80 K处归一化
Figure 4. Temperature-dependent integrated PL intensities (square) and average lifetimes(circle) of Mn∶ZnSe(2.6 MLs) (a) and Mn∶ZnSe(6.5 MLs)(b) QDs,the integrated PL intensities were normalized at 80 K
图 5 壳层厚度分别为2.6 MLs(a)和6.5 MLs(b)的Mn∶ZnSe量子点的发光积分强度在加热-冷却循环过程中的变化，黑色实心方块为升温过程，红色空心圆环为降温过程
Figure 5. Temperature-dependent integrated PL intensities of Mn∶ZnSe(2.6 MLs)(a) and Mn∶ZnSe(6.5 MLs)(b) QDs in heating-cooling cycle processes. Black solid squares refer to the heating processes,while red open circles represent the cooling processes
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