Not quite. This quasi particle is actually unstable. Two opposite cases would be a recombination process when the electron drops into the hole, and dissociation of excitons into the free electron and the free hole. The later process depends on the binding energy that holds the electron-hole pair together and the strength of the electric field (whatever the origin of the field could be: laser, interface etc.). The binding energy can vary from say, 4.3 meV ( GaAs) to 400 meV (KBr). Think about it as of a process of breaking a bond, for example. There is nothing special about it: just the strength of the bond vs. the strength of the electric field acting on the particle. There are some details peculiar to excitons, like tightly-bound Frenkel excitons and weakly-bound Mott-Wannier excitons, condensation of excitons into electron-hole drops at high exciton concentrations in Ge and Si at very low temperatures.

Most textbooks on solid state physics would give a pretty good picture of the subject.

P.S. I should have mentioned that temperature also affects the stability of the exciton (via kT vs. the binding energy).

Dear Colleagues,

Adding to colleague Sege,

The excitons are bound electron hole pairs and thereby needs some of energy to dissociate them producing free electrons and free holes. This ca be accompished by:

-heating as the thermal energy can break the bond of the excitons if it is sufficient.

- The electric field as the electric field can push the electrons and holes in the excitons away from each others separating them if it is greater than the binding force. So, it is not just right to say that that the electric field do not affect the excitons ad they form electric dipoles.

- The last method is extracting their electrons by contacting their parent molecules by acceptor molecules where the acceptor molecules have more affinity to electrons than their parent molecules.

Therefore you find the acceptor molecules lumolevels lies under that of the donor molecules.

Best wishes

Dear Sanjoy Paul

Interesting question, so I found the following in a Russian site by Profs. V. F. Agekyan and N. R. Grigoryeva:

Люминесценция полупроводниковых кристаллов В.Ф. Агекян, Н.Р. Григорьева

http://solid.phys.spbu.ru/ag_lum.html

(Luminescence of semiconductor crystals by V. F. Agekyan and N.R. Grigoryeva)

First, I must say that excitons as quasiparticles well behave as cuasi-stationary states, hereby they exist.

The link is:

http://solid.phys.spbu.ru/uploads/%D0%B0%D0%B3_4.pdf

The physical mechanism for dissociation is luminiscence in the following way:

Excitons bound on an ionized donor are destroyed as a result of successive separation from the system of the main hole, and then the electron (1,2).

1. [(+) eh] +E+, eh→ [(+)]+[e,h]; then [e, h] + G→e + h,

2. [(+) eh] +E+, eh + G→ [(+)] + e + h where G is the bound energy.

Another option for the destruction of excitons is the separation of exciton completely (3,4).

3. [(+) eh] +E[+, e],h→ [(+), e]+[h]; then [(+), e] + ED→ [(+)] + e

4. [(+) eh] +E_affinity + Eel_do→ [(+)] + e + h.

For example the initial state is an exciton ionized donor, and the final state is an ionized donor plus free electron hole (1).

Regards.

when excitons receive enough enough energy (high temperature, photo-induced, strong E-field) to break the binding energy, it will dissociate into electron and hole.

charge carriers are moving.so they having the kinetic energy.Due to this kinetic energy charge carriers are colloid with immovable charges.because of that collision electron and holes are created.

Generally we have 3 types of materials

1)conductors: the current can pass through it easily , that means electrons move freely. It consists full of free electrons..(no holes).

2)semiconductors: these are partially conductors, that means it requires some force (heat,temperature) to make the electrons as free to move for conducting electricity. As electron move from place to another place it leaves a hole behind,if force is applied. That's how Excitons get dissociated into free electron and hole.

3)insulator: it doesn't conduct electricity, because no free electron. Even if you apply force also it doesn't conduct.