AC electroluminescence with Zn2SiO4:Mn2+/CaSiO3:Ce3+ phosphor bilayer on silicon substrate

Abstract

A green-emitting electroluminescent device was fabricated by sequentially coating CaSiO₃:Ce³⁺ and Zn₂SiO₄:Mn²⁺ phosphors onto a silicon substrate to induce energy transfer within the bilayer structure. The phosphor thin films were synthesized using a combination of sol–gel and solid-state reaction methods, forming a stacked configuration of Zn₂ SiO₄:Mn²⁺/CaSiO₃:Ce³⁺/SiOₓ/Si. The CaSiO₃:Ce³⁺ layer was annealed at 1100 °C for 4 hours, followed by the annealing of the Zn₂SiO₄:Mn²⁺ layer at 900 °C, 1000 °C, and 1100 °C, respectively. Electrodes were then deposited on both sides of the device to evaluate its electrical and optical characteristics. At annealing temperatures of 900 °C and 1000 °C, all combinations of Ce- and Mn-doped calcium silicate and zinc silicate exhibited luminescence, indicating that both activators were effectively incorporated into their respective host lattices. However, at 1100 °C, only weak luminescence from CaSiO₃:Ce³⁺ was observed, while efficient energy transfer from the CaSiO₃:Ce³⁺ layer facilitated d–d transitions in Mn²⁺ ions within the Zn₂SiO₄:Mn²⁺ layer. The device exhibited a breakdown voltage of 41 V and achieved a luminance approximately seven times higher than that of a single-layer Zn₂SiO₄:Mn²⁺ device. Furthermore, the luminance decreased gradually rather than abruptly as the applied voltage was reduced from its maximum value. This study demonstrates that when dopant ion substitution is hindered by a significant ionic radius mismatch with the host matrix, a stacked thin-film architecture can promote optical interactions, such as energy transfer, between discrete phosphor layers. By employing various phosphor combinations, it is possible to overcome ionic radius limitations and expand the design possibilities for advanced electroluminescent materials.