What causes color change in powders during XRD testing?

[Secpia]

I was performing XRD earlier, and I came across this odd occurrence in the powders that were being inspected - After it was performed, the crystalline powder I had been testing had gone off color into this yellowish appearance (Originally was white). Upon disturbance, the powder become white again.

I asked around, but the only answer my associates could tell me is it was "color core displacement", but I haven't been able to find anything on this. Does anyone happen to know the term, or what it is? Very curious.

Admittedly XRD is not my specialisation, so apologies if it's something incredibly obvious.

 

[Lord Jestocost]

Generally, ionizing radiation like X-rays can induce changes in the physical properties of materials owing to the generation of defects, for example, color centers which are point defects/point defect clusters associated with trapped electrons/holes. Such "radiation damages" extend from the material’s surface roughly to an depth of the order of the penetration depth of the respective ionizing radiation (in case of X-rays this is the µm-range). In case of XRD measurements on powder batches, thus the uppermost layer of the powder batch is mainly affected.