Bo Fan

Near-infrared down-conversion in rare-earth-doped chloro-sulfide glass GeS2–Ga2S3–CsCl: Er, Yb

Chloro-sulfide glass with low phonon energy, GeS2–Ga2S3–CsCl, is co-doped with Er and Yb. This active glass is a potential downconversion material for modifying the solar spectrum to improve the efficiency of solar cells. Two downconversion processes from visible to near infrared are observed. In the first process, an energy transfer between Er3+ ions and Yb3+ ions occurs. In that case, one photon is absorbed by the 4I15/2→2H11/2 (Er3+) transition and then two photons are emitted by 2F5/2 →2F7/2 (Yb3+) and 4I13/2→4I15/2 (Er3+), respectively. In the second process, downconversion takes place from the charge-transfer state of Yb3+–S2− to the 4f states of Yb3+ ions, which leads to an intense excitation band between 400 nm and 600 nm, and an emission at 1000 nm. Quantum yields for downconversion are measured. The highest quantum yields of emission below 1200 nm and 1650 nm are equal to 51% and 76%, respectively.

Quantum cutting in Pr3+-Yb3+ codoped chalcohalide glasses for high-efficiency c-Si solar cells.

Downconversion materials, which can convert one high-energy photon to two low-energy photons, have provided a promising avenue for the enhancement of solar cell efficiency. In this work, the Pr3+-Yb3+ codoped 25GeS2-35Ga2S3-40CsCl chalcohalide glasses were synthesized in a vacuumed silica ampoule by the melting-quenching technique. Under 474 nm excitation, the visible and near-IR emission spectra reveal the energy transfer from Pr3+ to Yb3+ ions, resulting in the intense 1008 nm near-IR emission for the c-Si solar cells. By tuning the excitation laser power, it is determined that one visible photon has been cut into two near-IR photons during the energy transfer process. With the help of an integrated sphere, the real quantum yields of near-IR emissions were calculated. For the 0.2Pr2S3-0.2Yb2S3 (in mol.%) codoped chalcohalide glass, the quantum yield equals 10.8%. Although this efficiency is still low, this result will open a new route to realize the efficient spectral modification of the solar spectrum.

Yb 3+ -doped GeS 2 -Ga 2 S 3 -CsCl glass with broad and adjustable absorption/excitation band for near-infrared luminescence

The luminescent property of Yb(3+) ions in GeS(2)-Ga(2)S(3)-CsCl glasses with different CsCl contents has been studied. All the samples demonstrate a broad excitation band in the UV or/and visible range, depending on the composition, which is attributed to the charge transfer of the Yb(3+)-S(2-)/Cl(-) couple. The width of the excitation/absorption band can be as large as 150 nm. Moreover, with the increase of CsCl content, the peak position of the band can be continuously adjusted from 458 to 380 nm, due to the increase of the local average electronegativity around Yb(3+) ions. The broad and adjustable excitation band makes the Yb(3+)doped GeS(2)-Ga(2)S(3)-CsCl glass interesting for modifying the solar spectrum by absorbing strongly in the UV/blue region for emission around 1 μm. This kind of material is the key to adapting the solar spectrum to the response of silicon photovoltaic solar cells.

Towards ultra-broad emission band by luminescent film with continuously tunable emission wavelength

Abstract: Thin films of Ca1-xSrxS:Eu with tunable photoluminescence are fabricated by cathodic magnetron-assisted co-sputtering. Broad and intense luminescence has been observed, and its color shifts progressively from yellow to dark red by changing thin film composition. One promising application of these thin films is for improving the color rendering index of YAG:Ce-coated blue LEDs up to 93. Still broader emission is expected by creating a continuous composition gradient which can be realized by adjusting the power ratio applied on the two targets during the film deposition.