Yukun Li

Near infrared quantum cutting in heavy Yb doped Ce0.03Yb3xY(2.97-3x)Al5O12 transparent ceramics for crystalline silicon solar cells

Near infrared (NIR) quantum cutting involving the conversion of an absorbed blue photon into two NIR photons emission has been realized in heavy Yb doped Ce0.03Yb3xY(2.97−3x)Al5O12 (x=0.1, 0.25, and 0.5) transparent ceramics. Upon the 467 nm excitation, the energy transfer process was dominated by the cooperative downconversion from the 5d1 state of one Ce3+ ion to the F25/2 state of two Yb3+ ions. The influence of the Ce4+–Yb2+ charge transfer state (CTS) should not contribute much to the energy transfer process for the large energy gap between Ce3+:5d1 and the CTS. The calculated quantum yield of Yb3+ for the x=0.25 sample without concentration quenching was 175.4%.

The preparation and photoluminescence properties of ZnO-MCM-41

Abstract ZnO crystallites have been anchored within the pore channels of silica MCM-41 (named ZnO-MCM-41) through a chelation method of Zn2+ by ethyldiamino group (EN) on the inner surface. The structural and elemental composition analyses of the material were characterized by the SAXRD, XRD, BET, XPS and EDS under HRTEM techniques. The ZnO crystallites were about 1.7 nm estimated from the UV–Vis spectra. The bright UV (377 nm), violet (420 nm) and blue–green (480 nm) photoluminescence (PL) bands have been detected. The unfamiliar violet PL band is related to the oxygen vacancies on the ZnO–SiO2 interface traps.

Down-Conversion From Blue to Near Infrared in Tm

Down-conversion from blue to near infrared (NIR) has been demonstrated in Tm3+-Yb3+ codoped Y2O3 transparent ceramics. Upon the 464-nm excitation, the energy transfer (ET) mechanisms consisted of the Tm3+ : 1G4 → 2Yb3+ : 2F5/2 cooperative down-conversion and the phonon assisted Tm3+ : 1G4 + Yb3+ : 2F7/2 → Tm3+ : 3H5 + Yb3+ : 2F5/2 cross relaxation. The low quantum yield of the latter process, together with the low absorption cross section of Tm3+ at 464 nm and the low quenching concentration of Yb3+ in the Y2O3 host, made the Yb3+ 1030-nm NIR emission too weak for practical application.

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Tm3+/Yb3+ codoped Y2O3 transparent ceramics were fabricated and characterized from the point of upconversion luminescence. All the samples exhibited high transparency not only in near-infrared band but also in visible region. Under 980 nm excitation, the ceramics gave upconversion luminescence with very intense blue (485 nm) and considerably intense violet (360 nm) emissions. It was worthy to point out that the upconversion luminescence contained six emission bands, which dispersed in the region from 294 to 809 nm. The strongest blue emission (485 nm) was obtained with (Tm0.002Yb0.03Y0.958Zr0.01)2O3 ceramic (Yb/Tm=15). The mechanism of all upconversion emission bands were investigated in detail. The absorption, emission, and gain cross-section of blue emission (485 nm) were calculated, which indicated that Tm3+/Yb3+ codoped Y2O3 transparent ceramic has tremendous potential in short wavelength laser.