In the agent community, emotional aspects receive more and more attention since they were proven to be essential for intelligent agents. Indeed, from a theoretical point of view, results from cognitive psychology and neuroscience have established the close links that exist in humans between emotions and reasoning or decision making. And from a practical point of view, numerous research findings show the interest of emotions in agents communicating with humans: interface agents, pedagogical agents... However, among the logical frameworks used to formalize these `rational agents', very few integrate these emotional aspects. In this paper, we characterize some emotions, as defined in cognitive psychology, in a BDI (Belief, Desire, Intention) modal logic. We then validate our framework with a case study illustrating the problematic of Ambient Intelligence.