Elucidating the mechanism behind the significant changes in photoluminescence behavior after powder compression into a tablet†

Abstract

Nonconventional luminogens have great potential for applications in fields like anti-counterfeiting encryption. But so far, the photoluminescence quantum yield (PLQY) of most of these powders is still relatively low and the persistent room temperature phosphorescence (p-RTP) emission is relatively weak. To improve their PLQY and p-RTP, pressing the powder into tablets has been preliminarily proven to be an effective method, but the specific mechanism has not been fully elucidated yet. Here, D-(+)-cellobiose has been chosen as the representative to study the problem. The results showed that the PLQY and p-RTP lifetimes of the tablet of D-(+)-cellobiose were improved compared to those of the powder. Using the mechanism of clustering-triggered emission (CTE) and theoretical calculations, it has been demonstrated that the enhanced molecular interactions after compression are the key reason, which result in the formation of cluster emission centers with stronger emission capabilities. And the combination of the powder and tablet has been proven to have application potential for advanced anti-counterfeiting encryption. The above results not only provide possible references for understanding the emission mechanism of small molecules and cellulose based emission materials, but also promote the process of more intuitive observation of emission centers for explaining emission mechanisms.