Please any one reply...I am still waiting for expert answer....

Electroluminescence is the production of light by the flow of electrons where there is a direct conversion of electric energy into visible light without the generation of heat.

A perovskite like barium titanate (BaTiO3) is a common ferroelectric non stoichiometric substance possessing a high dielectric constant. It has a unique advantage as it has two types of ions [Ba (II) and Ti(IV)] which can be doped both with the trivalent donors (La, Y) normally substituting for the Ba (II) or with pentavalent donors (Sb, Nb, Ta) which substitute for Ti(IV) to make it a semiconductor that shows a PTCR( Positive Temperature Coefficient of Resistance) effect. The group 13th elements with three electrons after forming two covalent bonds with Ba (II) still has one free electon to conduct electricity in a normal way(n-type) . Similarly, the group 15th elements with five electrons after forming four covalent bonds with Ti (IV) also has one free electron to conduct electricity in a normal way(n-type).Still there can be the third case where the group 13th elements with three electrons after forming three covalent bonds with Ti (IV) leave one hole. Such holes can move across the crystal (p- type semiconductors) again giving rise to electrical conductivity. So BaTiO3 may act both n- type and p-type semiconductor. In such p-type semiconductors, the conductivity increases with the increase in temperature; a property unlike metals where reverse phenomenon is observed.

Dear Sir,

Thank you very much for your reply under this question. Sir, your answer given me good understanding related to BaTiO3. But, still I have some sort of further question that is "if BaTiO3 will use in electrolumniscence devices then this material will behave like dielectric or it should be semi-conductive (which is generally can be transform with high-temperature annealing)."

Please enlighten me further.

Thanks !!

Dear Vaseem,

Luminescence is the emission of light from a material when excited electrons in it drop to lower energy empty electronic states. If the excited electrons are produced by electrical energy , the luminescence is an eletroluminescence . While it will be termed photoluminescence when the excited electrons are produced by incident energetic photons. This phenomenon occurrs in the light emitting diodes where the excess excited electrons in the conduction band recombine with holes in the valance band producing light with a photon energy equals the the energy gap of the materials. If this electron transfer is direct without change in momentum. the probability of this transition will be larger and the light emitting efficiency will be larger. Electron transfer can occurr also between the energy bands and energy levels produced in the energy gap and even between the energy levels inside the energy gap . These allowed energy levels in the energy gap can be produced either by doping impurities or due to crystallographic disorder. These levels serve as trapping levels and recombination centers.

This is the concept of the luminescence in general and applies also for the emission of light from films of barium titanate when properly excited. As an example for the role of bariumtitanate as a luminescence material the paper in the link may be useful: http://www.cmdmc.com.br/redecmdmc/lab/arquivos_publicacoes/2780_Photoluminescence%20of%20Barium%20Titanate%20and%20Barium%20Zirconate%20in%20Multilayer%20Disordered.pdf

I hope i shed some light on this interesting topic.

Thank you for question

Dear Abdelhalim Zekry Sir,

Thanks for your reply over this topic and put forward some of the concept related to this. Thanks for the link also.

Dear Vaseem - Not sure if its still relevant to you. Basically in EL device BaTiO3 is useful to overcome short circuit as ACEL operating voltage is high and on the other hand it helps to reflect light being white reflector. Prerequisites - layer has to be thin and its dielectric constant should be as high as possible. Hope that helps.