An inorganic electroluminescent device using calcium phosphate doped with Eu3+ as the luminescent layer

In this work, the availability of calcium phosphates for the light emitting layer of a thin-film electroluminescent (TFEL) device was investigated. The goal of this work was to develop an electronic device with ordinary materials such as a calcium phosphate, the principal ingredient of the skeleton of the vertebrate. Compositions of 2CaO·P2O5 (Ca2P2O7), 3CaO·P2O5 (Ca3(PO4)2) and 4CaO·P2O5 (Ca4O(PO4)2) were examined as the candidates for the light emitting layer. Before composing the TFEL device, the photoluminescence (PL) properties of the three compositions were investigated in the powder form to evaluate the performance as the light emitting layer. Among the examined calcium phosphates, Eu-doped β-Ca3(PO4)2 showed the best PL properties. It showed typical red-emission from Eu3+. The PL intensity was enhanced with the heat-treatment temperature and the optimal temperature was 1250 °C. Then, a TFEL device was prepared by a spray pyrolysis method with the β-Ca3(PO4)2:Eu3+ phosphor layer on a BaTiO3 disk. The TFEL device exhibited the red emission originating in Eu3+ at 610 nm under applying alternating voltage. Different from the power sample, the intensity of EL decreased with the heat-treatment temperature from 1000 to 1250 °C. The deterioration of EL at the higher temperatures was attributed to chemical interaction between the phosphor layer and the BaTiO3 disk.

► A thin film electroluminescent device was fabricated with a calcium phosphate as the light emitting layer. ► The light emitting layer was formed on the BaTiO3 disk by a spray pyrolysis method. ► Among the examined calcium phosphates, β-Ca3(PO4)2:Eu3+ showed the best photo- and electroluminescent properties.