Triboluminescence modulated by humidity

Triboluminescence (TL) reflects the characteristics of real-time optical signals generated in the process of friction, hence is promising in real-time monitoring and surface study. By studying the sliding between SiO2 and Al2O3, we found that triboluminescence can be modulated quantitatively by modifying ambient humidity. The trend of TL intensity varies at different ranges of humidity and there exists a critical humidity. TL intensity rises initially and reaches its peak at critical humidity before it diminishes and eventually decreases to zero. It results from the decrease of energy barrier of tribo-charging and the increase of electric field intensity below critical humidity, and for humidity above critical humidity, the rapid growth of surface conductivity and a shorter distance account for smaller possibility of gas collision.