STRUCTURE AND OPTICAL ABSORPTION OF AGI MICROCRYSTALS
STRUCTURE AND OPTICAL ABSORPTION OF AGI MICROCRYSTALS
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DOI：
10.1103/physrev.161.848
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发表时间：
1967-01-01
期刊：
影响因子：
--
通讯作者：
BERRY, CR
中科院分区：
文献类型：
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作者：
BERRY, CR
对六方AgI标准粉末衍射图的x射线强度提出了较大的修正。根据这些强度，似乎一些在文献中被描述为纯六边形的沉淀物实际上含有大约30%的立方相。在沉淀过程中，仅通过缓慢结晶产生六方AgI，并且没有过量的Ag+或I−。更快的沉淀得到了立方相和六方相的混合物，以及平均直径为150 Å的晶体。这些悬浮液的瑞利散射足够小，可以很容易地测量晶体的吸收系数。在小晶体中没有420 μ左右的激子吸收峰。当晶体生长时，随着晶体尺寸的增大，晶体的激子峰略低于420 μ m，而随着晶体尺寸的增大，晶体的激子峰略高于420 μ m。在同样小尺寸的晶体中，激子区AgI的吸收下降幅度远大于AgBr的吸收边缘。与AgBr相比，AgI吸收损失的其他机制显然是明确指出的。这表明AgI中的激子半径太大，以至于激子不能在靠近表面的地方形成。
Large corrections to the x-ray intensities of the standard powder diffraction pattern of hexagonal AgI are proposed. Based on these intensities, it appears that some precipitates which have been described in the literature as pure hexagonal have actually contained about 30% of the cubic phase. Hexagonal AgI was produced during precipitation only by slow crystallization and without an excess of either Ag+ or I−. Faster precipitations gave mixtures of the cubic and hexagonal phases, and crystals whose average diameter was as small at 150 Å. The Rayleigh scattering of these suspensions was sufficiently small that the absorption coefficients of the crystals could be readily measured. The usually strong exciton absorption peak at about 420 mμ was missing in the small crystals. When the crystals were made to grow, the exciton peak appeared slightly below 420 mμ for crystals which became more hexagonal as they increased in size, and somewhat above 420 mμ for crystals which became more cubic. The decrease in absorption for AgI in the exciton region was much more than for the absorption edge of AgBr for crystals of comparable small size. Additional mechanisms for the loss of absorption in AgI compared with AgBr are apparently indicated. It is suggested that the exciton radius in AgI is so large that the exciton cannot be formed close to the surface.