Spectroscopic investigation of indium bromide for lighting purposes
Spectroscopic investigation of indium bromide for lighting purposes
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照明用溴化铟的光谱研究
DOI：
10.6100/ir657962
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
Hcj Hjalmar Mulders
中科院分区：
文献类型：
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作者：
Hcj Hjalmar Mulders
在现代社会，光的存在被认为是理所当然的，但它是有代价的。今天我们所有人消耗的大部分能源用于照明：占总用电量的20%。在能源变得越来越稀缺和昂贵的世界里，高效的照明变得越来越重要。有几种不同的灯设计被用来提高白炽灯的效率：人类第一次尝试电灯。目前备受关注的一项新技术是发光二极管（LED），虽然这项技术在未来有很大的前景，但在可预见的未来，这项技术的一个主要问题将是每单位的采购价格。其他常用的技术有低压放电灯和高压放电灯。低压放电灯以荧光灯的形式为人所知。这种灯通过低压汞放电来工作，它可以非常有效地产生紫外线光子，然后将其转换为可见光，效率略低。高压放电灯是商店照明中常见的一种。它的工作原理是通过高压汞放电直接发射可见光，其中含有一些（通常是金属卤化物）添加剂。高压排放条件使排放效率降低。然而，这两种放电的产光效率是相当的(?？100 lm / W)。理想情况下，放电灯应该像低压放电灯那样，将高放电效率与直接产生可见光结合起来。为了做到这一点，设想了一种直接产生光的中压灯。产生光的种类不能与低压灯或高压灯相同。建议溴化铟作为研究的模式种。将研究溴化铟的光谱，以找到最佳的操作条件以及分子的基本性质。为此，设计并建立了激光诱导荧光实验。直径为3厘米，长度为30厘米的圆柱形管被安置在一个烤箱里，在管的体积上提供均匀的温度。激光束可以通过管的轴向照射，为所研究的分子提供激发。所使用的激光要么是YAG激光器的4次谐波，要么是由YAG泵浦激光器的3次谐波泵浦的高重复率（1 kHz）可调谐染料激光器。高重复频率是必要的，以防止饱和效应，同时仍然能够测量有意义的荧光光谱。荧光在垂直方向上被检测到。荧光光子被引导通过单色仪，然后被用于光谱分辨率的iCCD相机或连接到用于时间分辨率的多通道标尺的光电倍增管检测。在光谱分辨LIF测量中，激发波数和探测波数都覆盖一定的波数范围。为了解释光谱分辨的LIF数据，引入了所谓的分辨图。检测图显示荧光发射的彩色编码，检测波长在横轴上，激发波长在纵轴上。这些图对振动谱的解释很有帮助。在检测器图中可见的前所未有的细节使光谱的解开比以前可能的更好。这样就可以更精确地测定各种光谱常数。精细图有助于生成旋转转换列表，但是这些列表的开头通常是缺失的。为了仍然能够为观测到的跃迁分配正确的旋转量子数，基于未知旋转常数必须与附近能级的旋转常数相似的假设，开发了一种方法。该方法也可用于测定其它物质的旋转常数。可以看出，随着波数的增加，衰减时间逐渐减小。在较高的波数和较高的旋转量子数下，由于分子中化学键的拉伸，核间距离增加。一般来说，核间距离越长，跃迁概率越高，但它也会导致分子在几何上更大。换句话说，高激发态InBr分子的碰撞截面可能比基态InBr分子大。本文采用两种方法来确定等离子体的旋转温度：一种是强度法，用改进的玻尔兹曼分布来拟合旋转峰的强度；另一种是拟合法，用计算机程序根据已知的光谱常数来拟合整个光谱。这两种方法都被证明能够确定气体中的温度，其中由拟合方法发现的温度的准确性似乎（可以预见）略好一些。拟合的结果精度为？？强度法获得的精度为？？25 - 30%。使用这种方法来确定感应等离子体中的温度被证明是不可能的，因为在感兴趣的区域没有InBr荧光。在266nm激发下的实验表明，InBr分子间的碰撞对所设想的灯的典型工作温度下的弛豫过程有非常显著的贡献。在电感耦合等离子体上进行的测量证实了这一点，在等离子体最亮的部分没有分子辐射。由此得出结论，InBr放电产生的辐射中的分子成分（强烈地）受到碰撞弛豫过程的限制。当然，铟本身也是一种强辐射原子，所以将铟（可能以铟溴的形式）作为灯的化学混合物的添加剂并不是绝对不明智的。然而，InBr分子可以作为中压灯主辐射体的候选材料而被丢弃。
In the modern world, the presence of light is taken for granted, but it comes at a cost. A large portion of the energy that is consumed by all of us today is used for lighting: 20% of the total electricity consumption. In a world where energy is becoming increasingly scarce and expensive, efficient lighting becomes more and more important. There are a few different lamp designs that are used to improve on the efficiency of the incandescent lamp: man’s first attempt at electric lighting. A new technology that is receiving a lot of attention currently is the light emitting diode (LED), and while this technology holds a great promise for the future, a major issue with this technology will be the purchase price per unit for the foreseeable future. Other commonly known technologies are the low pressure discharge lamp and the high pressure discharge lamp. The low pressure discharge lamp is known in the form of the fluorescent tube. This lamp works via a low pressure mercury discharge that produces UV-photons very efficiently that it then converts to visible light somewhat less efficiently. The high pressure discharge lamp is often seen in shop lighting. It works by the direct emission of visible light from a high pressure mercury discharge that has some (usually metal halides) additives in it. The high pressure discharge conditions make for a less efficient discharge. However, the light production efficiency of both these discharges is comparable (?? 100 lm/W).Ideally, a discharge lamp would combine a high discharge efficiency, like the low pressure discharge lamp has, with the direct production of visible light. To do this an intermediate pressure lamp is envisioned that produces light directly. The light producing species can not be the same as in the low or high pressure lamps. Indium Bromide is suggested as a model species to study. The spectrum of Indium Bromide will be studied to find optimal operating conditions as well as fundamental properties of the molecule. To do this, a laser induced fluorescence experiment is designed and built. A cylindrical tube with a diameter of 3 cm and a length of 30 cm is housed inside an oven that provides a homogenous temperature over the volume of the tube. Axally through the tube, a laser can be shone that provides excitation of the studied molecules. The laser used is either the 4th harmonic of a YAG laser or a high repetition rate (1 kHz) tunable dye laser which is pumped by the 3rd harmonic of a YAG pump laser. The high repetition frequency is necessary to prevent saturation effects, while still being able to measure meaningful fluorescence spectra. The fluorescence is detected in a perpendicular direction. The fluorescence photons are guided through a monochromator and then detected by either an iCCD camera for spectral resolution or a photomultiplier tube connected to a multichannel scaler for time resolution. In spectrally resolved LIF measurements both the excitation wave number and the detection wave number cover a certain wave number range. For the interpretation of the spectrally resolved LIF data, the so-called detex plots were introduced. A detex plot shows the fluorescence emission colorcoded in a graph with the detection wave length on the horizontal axis and the excitation wavelength on the vertical axis. These plots are very helpful for the interpretation of rovibronic spectra. The unprecedented detail visible in the detex plots enables a better unraveling of spectra than previously possible. This enabled the determination of various spectroscopic constants with greater accuracy. The detex plots helped produce lists of rotational transitions, however the beginning of these lists was generally missing. To still be able to assign the correct rotational quantum number to the observed transition, a method was developed based on the assumption that the unknown rotational constant must be similar to the rotational constant of a level nearby. This method can be useful in the determination of rotational constants for other species too.It can be seen that the decay time decreases gradually with increasing wave number. At higher wave numbers, and therefore higher rotational quantum numbers, the internuclear distance increases due to stretching of the chemical bonds in the molecule. In general, a higher internuclear distance is associated with a higher transition probability, but it also leads to a geometrically larger molecule. In other words, the collisional cross section for an InBr molecule in a highly excited rotational state may be larger than for a ground state InBr molecule. Two methods were used to determine the rotational temperature of a plasma:The intensity method, where the intensities of the rotational peaks is plotted and fitted with a modified Boltzmann distribution, and the fitting method, where the whole spectrum is fitted with a computer program based on the known spectroscopic constants. Both methods have been shown to be able to determine the temperature in a gas, where the accuracy of the temperature found by the fitting method seemed to be (predictably) slightly better. The fitting method yielded results with an accuracy of ?? 10-15%, whereas the achieved accuracy for the intensity method was of the order of ?? 25 - 30%. Using this method to determine the temperature in an inductive plasma proved to be impossible, due to the absence of InBr fluorescence in the region of interest. The experiments with the 266 nm excitation showed that collisions between InBr molecules contribute very significantly to the relaxation processes at temperatures typical for the operation of the envisioned lamp. This was confirmed by the measurements performed on the inductively coupled plasma, where molecular radiation was absent in the brightest part of the plasma. This leads to the conclusion that the molecular component in the radiation produced by an InBr discharge is (strongly) limited by the collisional relaxation processes. Indium itself is of course also a heavily radiating atom, so the use of Indium (perhaps in the form of InBr) as an additive to a chemical mix for a lamp is not categoricaly deemed as unwise. However the molecule InBr can be discarded as a candidate to be the primary radiator in an intermediate pressure lamp.