Plastic Material that will not Fluoresce at a wave length of 500 nanometers

I have an application where our part requires no fluorescence at 480-530 nanmoeters under an array of LED lights. We currently use a
styrene co-polymer that has worked in the past, but recently has failed. We are chasing down the root cause with no luck. My question is this:
1 - What will cause a material to not fluoresce? 2 - Does anyone know of alternate materials?
Thank you very much for your response!
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