A broadband‐sensitive upconverter: Garnet‐type Ca₃Ga₂Ge₃O₁₂ codoped with Er³⁺, Y³⁺, Li⁺, Ni²⁺, and Nb⁵⁺

Abstract

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 energy transfer from the Ni2+ to the Er3+. Formation of four‐coordinated Ni2+ that quenches the UC emission of the Er3+ was prevented, because Ni2+ cannot substitute the four‐coordinated Ge4+ much smaller than Ni2+. Consequently, energy dissipation from the Er3+ to the Ni2+ was well reduced compared with the previously developed Gd3Ga5O12:Er,Ni,Nb in which the Ni2+ dopants partially occupied the four‐coordinated Ga3+ sites. Additional introduction of Y3+ and Li+ enhanced optical transitions and improved the UC performance, owing to more enhanced lattice distortion, along with eliminating different phases. The optimal composition (Ca0.6Er0.1Y0.1Li0.2)3(Ga0.98Ni0.01Nb0.01)2Ge3O12 exhibited a broadband sensitivity ranging from 1.1 μm (the absorption edge of silicon) to 1.6 μm for the UC emission at 0.98 μm.

Improving the efficiency of upconversion by light concentration using nanoparticle design

“…In all but the most trivial cases no analytical solution exists for (81)- (83). Therefore, the design field and the physical model problem(s) must be discretized in space, using, for example, the finite element method [49], as described in section 3 and illustrated in figure 15(d), and solved to obtain approximate solutions 6 . This discretization results in the design field being represented by N ξ ∈ N continuous design variables.…”

“…At present, the best candidate is PbS nanocrystals [4], which however are not environmentally friendly due to the presence of lead. In another approach, absorption of 1.1-1.45 µm by Ni 2+ ions and subsequent energy transfer to neighboring Er 3+ ions has been realized to achieve broadband upconversion to 980 nm [5,6]. The present review will also not discuss spectral conversion of sun light in a broader sense, which can be found elsewhere [7].…”

Broad-band sensitized visible up-conversion in Y2Mg3Ge3O12:Ni2+,Er3+,Nb5+ phosphors

“…29,30 Similarly, UC emission of Er 3+ /Tm 3+ sensitized by Ni 2+ has also been realized in phosphors such as (Mg, Ca, Sr, Ba)TiO 3 :Ni 2+ ,Er 3+ , MgGa 2 O 4 :Ni 2+ ,Er 3+ , LiGa 5 O 8 :Ni 2+ ,Tm 3+ , La(Ga, Sc, In)O 3 :Ni 2+ ,Er 3+ , etc. 31–37 Therefore, Ni 2+ sensitized UC phosphors might be promising materials for up-converting photons in a wide near infrared wavelength region into a higher energy photon due to the broad band absorption of Ni 2+ .…”

“…29,30 Similarly, UC emission of Er 3+ /Tm 3+ sensitized by Ni 2+ has also been realized in phosphors such as (Mg, Ca, Sr, Ba)TiO 3 :Ni 2+ ,Er 3+ , MgGa 2 O 4 :Ni 2+ ,Er 3+ , LiGa 5 O 8 :Ni 2+ ,Tm 3+ , La(Ga, Sc, In)O 3 :Ni 2+ ,Er 3+ , etc. [31][32][33][34][35][36][37] Therefore, Ni 2+ sensitized UC phosphors might be promising materials for up-converting photons in a wide near infrared wavelength region into a higher energy photon due to the broad band absorption of Ni The weighed raw materials were fully ground and mixed in an agate mortar, and the mixtures were subsequently transferred into corundum crucibles. The mixtures were calcined at a temperature of 1500 1C for 7 hours in an electric furnace under an air atmosphere.…”