Anisotropic photoluminescence properties of oriented poly( p -phenylene-vinylene) films: Effects of dispersion of optical constants
Anisotropic photoluminescence properties of oriented poly( p -phenylene-vinylene) films: Effects of dispersion of optical constants
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取向聚（对亚苯基亚乙烯基）薄膜的各向异性光致发光特性：光学常数色散的影响
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发表时间：
2007
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通讯作者：
D. Moses
中科院分区：
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作者：
C. Soci;D. Comoretto;F. Marabelli;D. Moses
本文报道了色散光学常数对高取向聚苯乙烯薄膜各向异性光致发光光谱的影响。偏振透射率、反射率和光致发光光谱在不同温度下的宽光谱范围内进行了测量。由于聚合物薄膜中具有高度的链取向，其发射特性具有高度的各向异性。聚合物薄膜内部的自吸收和聚合物-空气界面处的折射效应对PL光谱形状和外量子效率有显著影响。为了阐明这些方面，我们确定了复介电常数$({ensuremath{epsilon}}_{1}+i{ensuremath{epsilon}}_{2})$的平行和垂直分量的色散，并据此根据菲涅耳方程对PL谱进行了校正。修正后发现，当激发方向与拉伸方向垂直极化时，PL强度更高，我们将这一事实归因于电荷诱导的PL猝灭。我们还考虑了折射率对PL自发发射率和聚合物膜光提取的影响。校正后的PL光谱的发射各向异性函数的光谱依赖性表明存在两种不同的发射物质，它们可能来自分子内和分子间状态。
We report on the effects of dispersive optical constants on the anisotropic photoluminescence spectra of highly oriented poly($p$-phenylene-vinylene) films. Polarized transmittance, reflectance, and photoluminescence (PL) spectra have been measured over a broad spectral range, at different temperatures. Due to the high degree of chain orientation in the polymer films, the emission properties are highly anisotropic. The PL spectral shape and external quantum efficiency are significantly affected by self-absorption inside the polymer film and by refractive effects at the polymer-air interface. In order to elucidate these aspects we have determined the dispersion of the parallel and perpendicular components of the complex dielectric constant $({ensuremath{epsilon}}_{1}+i{ensuremath{epsilon}}_{2})$, by which the PL spectra have been corrected according to Fresnel equations. After correction, the PL intensity is found to be higher when the excitation is polarized perpendicular to the stretching direction, a fact that we attribute to charge-induced PL quenching. We have also considered the influence of the refractive index on the PL spontaneous emission rate and on the light extraction from the polymer film. The spectral dependence of the emission anisotropy functions of the corrected PL spectra indicates the presence of two distinct emitting species, which may originate from intramolecular and intermolecular states.