The Preparation And Near-Infrared Quantum Cutting Of Rare Earth Doped Oxyfluoride Glass Ceramics

Quantum cutting, which could generate two low energy photons for each incident high energy photon absorbed, has attracted great interest for its potential applications in the fields of photovoltaic applications. In silicon solar cells, by using quantum cutting, thermalization losses can be largely reduced, which can divide a photon with twice the energy of the band gap into two photons with exactly the energy of the band gap. In this way, the cell efficiency can be improved. Oxyfluoride glass ceramics are more appropriate for quantum cutting applications due to their excellent luminescent properties as well as high chemical durability and mechanical strength.In order to obtain transparent nano-structured glass ceramics, as near-infrared quantum cutting materials, in this paper oxyfluoride glass forming ability and crystallization properties of Pr3+-Yb3+codoped oxyfluoride glass ceramics containing CaF2 nanocrystals were studied. The glass ceramics heat treatment, microstructures and near-infrared quantum cutting fluores-cence of glass ceramics were illustrated, and the relationship among them was described.Compared the glass forming ability and crystallization ability of different composition, the formula of 55SiO2-5Na2O-20Al2O3-20CaF2 was chosen as the rare earth doped basis glass. The crystallization mechanism was analyzed by kinetics method, which showed that crystallization activation energy is 347.4kJ/mol, Avrami index is 1.87, and the crystallization is controlled by diffusion. The structure of nanocrystals in glass ceramic was illustrated by XRD, SEM, and EDS. The results indicate that the main phase is CaF2 nanocrystal sized at 30nm, and the incorporation of Pr3+and Yb3+into CaF2 nanocrystal lattice is confirmed by EDS directly and XRD indirectly.Infrared quantum cutting involving Yb3+980nm and 1015nm (2F5/2→2F7/2) emission is achieved upon the excitation of the 3P0 energy level of Pr3+at 482nm in Pr3+-Yb3+codoped oxyfluoride glass ceramics. With the increase of Yb3+concentration, the near infrared emission at 980 and 1015 nm intensifies rapidly, while the emission at visible region weakens monotonically. The fluorescence lifetime decreases sharply and quantum efficiency increases, and the optimal quantum efficiency reaches 191%.With improving the heat treatment temperature or extending insulation time, the overall emission intensity in visible region is enhanced, and emission peaks do not change obviously, while the emission peaks in near infrared region increase, which shows there is no substantial increase of Pr3+ions radiative transition probabilities, on the contrary the energy transfer probability increases between Pr3+ and Yb3+. In addition, calculations show that the efficiency of energy transfer and the total quantum efficiency are improved.