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首页> 外文会议>IUPAC 10th International conference on novel materials and their synthesis: Book of abstracts >ANALYSIS OF ENERGY UP-CONVERSION PROCESS OF ZNO VIA INTERMEDIATE STATE BY PHOTOLUMINESCENCE
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ANALYSIS OF ENERGY UP-CONVERSION PROCESS OF ZNO VIA INTERMEDIATE STATE BY PHOTOLUMINESCENCE

机译：光致发光分析ZNO通过中间态的能量上转换过程

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Energy up-conversion process is a candidate to improve the conversion efficiency of solar cells. The process via quantum dot is applied but that via intermediate state is not. This is because the mechanism via intermediate state has not been clarified. The up-conversion is, however, observed in ZnO and GaN. The mechanism is discussed here, since we found a state in ZnO by photoluminescence (PL), which was probably the origin of the up-conversion process of anti-Stokes PL (ASPL). The near band edge (NBE) ASPL at around 3.28 to 3.38 eV was observed at 5 K with 441.6 ran He-Cd laser excitation from cap-annealed ZnO crystals. The spectrum of the NBE ASPL was the same as the Stokes PL excited by 325.0 nm excitation. This shows that the ASPL process is two-step two-photon absorption. An intermediate localized state is required for the process which has the characteristics that photo generated electron from valence band relaxes thermally and the relaxed electron is re-excited to conduction band by another photon. Well-known state in ZnO is green luminescence (GL) with 2.40 eV peak. Recently, yellow luminescence (YL) with 2.25 eV peak was found after light turned-off with anti-Stokes excitation of 441.6 nm. Comparing the GL and YL, YL was related with the ASPL because the order of the excited intensity of YL was almost the half of that for NBE. The YL was found to be highly compensated D-A pair luminescence with tunneling from the peak shift dependency on the excited intensity and to have very long life time over us order. Hypothesizing the excited electron is the same for the GL and YL, YL is assumed to be originated from a lattice-relaxed deep trap. This lattice relaxation probably affects to the internal motion of D-A pair changed from s-orbital-like to p-orbital-like. This change probably semi-prohibits the light-emitting recombination of the D-A pair and allows the re-excitation to conduction band.
机译：能量上转换过程是提高太阳能电池转换效率的候选方法。应用通过量子点的过程，但不应用通过中间状态的过程。这是因为尚未阐明通过中间状态的机制。但是，在ZnO和GaN中观察到上转换。由于我们通过光致发光（PL）在ZnO中发现了一种状态，因此在这里讨论了该机理，这可能是反斯托克斯PL（ASPL）上转换过程的起源。在5 K下，通过帽盖退火ZnO晶体的441.6 nm He-Cd激光激发，在3.28至3.38 eV处观察到了近带边缘（NBE）ASPL。 NBE ASPL的光谱与通过325.0 nm激发激发的Stokes PL相同。这表明ASPL过程是两步两光子吸收。该方法需要中间的局部状态，该状态具有以下特征：从价带产生的光生电子热弛豫，并且另一电子将弛豫的电子重新激发到导带。 ZnO中众所周知的状态是具有2.40 eV峰值的绿色发光（GL）。最近，在以441.6 nm的反斯托克斯激发光熄灭后，发现具有2.25 eV峰值的黄色发光（YL）。比较GL和YL，YL与ASPL有关，因为YL的激发强度的顺序几乎是NBE的一半。 YL被发现是高度补偿的D-A对发光体，具有峰移对激发强度的依赖性，并且在我们的订单中具有很长的使用寿命。对于GL和YL，激发电子的假设是相同的，假定YL是源自晶格松弛的深陷阱。这种晶格弛豫可能影响D-A对的内部运动，该运动从s轨道状变为p轨道状。这种变化可能会半禁止D-A对的发光重组，并允许重新激发到导带。

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