[10a-S223-1~10] 13.8 Optical properties and light-emitting devices

[10a-S223-9] Broadband-sensitive upconversion emission of Er³⁺, Ni²⁺-co-doped Ca₃Ga₂Ge₃O₁₂ garnet

〇Yasuhiko Takeda¹, Shintaro Mizuno¹, Hom Nath Luitel¹, Toshihiko Tani¹ (1.Toyota Central R&D Labs.)

Keywords:upconversion, erbium, crystalline silicon solar cells

We have developed a new broadband-sensitive photon upconversion (UC) material that can be used for transparent ceramic plates mounted on the rear faces of crystalline silicon solar cells. We selected the host material of a cubic crystal structure codoped with Er³⁺ and Ni²⁺ so that the Ni²⁺ dopants were fully activated to sensitize the Er³⁺ emitters. In garnet-type Ca₃Ga₂Ge₃O₁₂ with additional codopants of Nb⁵⁺ and Li⁺ for charge compensation, all the Ni²⁺ dopants occupied the six-coordinated Ga³⁺ sites, leading to highly efficient sensitization. Formation of four-coordinated Ni²⁺ that quenches the UC emission of the Er³⁺ was prevented, because four-coordinated Ni²⁺ is much smaller than four-coordinated Ge⁴⁺. Additional introduction of Y³⁺ and Li⁺ enhanced lattice distortion and consequently improved the UC performance. Thus, the synthesized powder sample exhibited a broadband sensitivity ranging from 1.1 um (the absorption edge of crystalline silicon) to 1.6 um for the UC emission at 0.98 um.