1. Excitation: An atom absorbs energy, causing an electron to jump to a higher energy level, leaving the atom in an excited state. This energy can come from various sources like:
* Absorption of light: A photon of light with the right energy is absorbed by the atom.
* Collision with other atoms or molecules: Kinetic energy is transferred to the atom during collisions.
* Chemical reactions: Energy released in chemical reactions can excite an atom.
2. Emission: The excited atom is unstable and wants to return to its more stable ground state. It releases the excess energy as a photon of light, causing the electron to drop back down to its original energy level.
There are two main types of emission:
* Spontaneous Emission: This occurs randomly, with no external influence. The excited atom simply releases a photon and returns to the ground state.
* Stimulated Emission: This occurs when an external photon with the same energy as the energy difference between the excited state and the ground state interacts with the excited atom. This interaction stimulates the excited atom to emit another photon of the same energy and phase as the incident photon. This is the principle behind lasers.
Key points to remember:
* The energy of the emitted photon corresponds to the energy difference between the excited state and the ground state.
* The process of emission is governed by the laws of quantum mechanics.
* The lifetime of an excited state varies depending on the specific atom and energy level.
Examples:
* Neon signs: Neon atoms are excited by an electric current. They release photons of red light when they return to their ground state, creating the characteristic glow.
* Fluorescent lights: Mercury vapor is excited by an electric current, emitting ultraviolet light. This ultraviolet light then excites phosphor molecules on the inside of the bulb, which then emit visible light.
Understanding how excited atoms return to their ground state is crucial for various fields, including spectroscopy, lasers, and astrophysics.
