绿黄色磷灰石热处理紫外可见光谱研究

绿蓝色磷灰石因其颜色和"帕拉伊巴"绿蓝色碧玺相似而为消费者所熟知。为了验证此种磷灰石颜色是否经过人工处理,将不同颜色的磷灰石样品分别置于空气气氛下进行400~800℃的热处理。结果表明绿黄色磷灰石经过650℃的热处理就可产生绿蓝色。根据热处理过程中样品的X射线粉末衍射数据,在热处理过程中并未发生相变。为了进一步研究热处理过程中样品颜色的变化行为和实验参数对热处理效果的影响,将绿黄色磷灰石样品分别置于空气和还原气氛下进行300~800℃的对比热处理实验。结果显示不同气氛下样品颜色的变化行为十分相似。因此这也表明绿黄色磷灰石颜色的改变和元素价态的变化没有直接关联。室温下样品的紫外可见吸收光谱(200~800 nm)主要表现在蓝紫区强烈吸收,红橙区有一宽缓的吸收带(620~720 nm),黄绿区透过,出现了515, 528, 578, 739和747 nm等一系列吸收峰。随着热处理温度的升高,样品在可见光范围内的吸收系数大幅降低颜色变浅,吸收截止边逐渐蓝移导致样品逐渐呈现蓝色。与此同时,随着温度升高至400℃, 620~720 nm吸收带中最强吸收峰位置会发生蓝移导致样品的黄色调减弱。当温度达到800℃时,样品褪色, 620~720 nm吸收带消失,但515, 528, 578, 739和747 nm等一系列吸收峰仍然存在。因此绿黄色磷灰石在热处理过程中颜色的变化主要和吸收截止边以及620~720 nm吸收带的变化有关。

The UV-Vis Spectral Study on Thermal Treatment of Yellowish-Green Apatites

Recently, a special kind of apatites in the gem trade has been popular for its charming color which is similar to "Paraiba" bluish-green tourmaline. In order to prove whether the color of this apatite is processed, this paper put apatite samples with different colors respectively in the air atmosphere heated from 400 to 800 ℃. The experimental results show that, after heated at 650 ℃, yellowish-green samples can be changed into bluish-green. With temperature adding up to 800 ℃, all samples’ color were vanished. According to X-ray diffraction data, there is no phase transformation during the treatment. Subsequently, some yellowish-green samples are treated with different experimental parameters. Results show that the color change of samples is very similar in both air atmosphere and reducing atmosphere, which indicates that the color change is not related to the variation of the valence states. The UV-Vis spectra(200~800 nm) obtained at room temperature show that there are three apparent regions: a strong absorption between 300 and 450 nm, a transmittance from 450 to 550 nm, and a wide absorption band between 620 and 720 nm. Besides, there are some tiny peaks at 515, 528, 578, 739 and 747 nm. With the increase of temperature, the absorption coefficient of the samples is decreased significantly, causing color light. The absorption edge shifts to short wavelength, which reduces the absorption in the blue region and makes sample bluer. When the temperature reaches 400 ℃, the maximum absorption position in 620~720 nm displays a blue-shift resulting in less yellow tone. In the following, the absorption in 620~720 nm disappear and the color of sample vanish for the absorption coefficient keeping at a low level when the temperature adds up to 800 ℃. However, those tiny peaks still exist. Therefore, the color change in the heat treatment process is mainly related to the absorption edge and 620~720 nm absorption band.