The Preparation And Luminescence Properties Of Rare Earth Ions Doped Luminescent Glass Ceramics

This thesis described an overview of recent developments of phosphor convert materials for white LEDs, including red, green and blue tri-color phosphors, and the UV and near UV LED chip excited white phosphor converts. And then the novel rare earth doped glass ceramics, which can be used for the white LEDs, were prepared.Eu2+doped glass ceramics containing CaF2, SrF2, BaF2 nanocrystals were studied as blue phosphors for near UV LEDs. The Eu2+ions in the glass ceramics could be excited by broad band from 300 to 420 run, showing excellent overlap with the main emission region of a near UV LED chip, therefore it could be used as potential blue emitting phosphors. With increasing the concentration of Eu2+ concentration quenching that originated from quadrupole-quadrupole interactions with a critical content as 2.0 mol% was observed in the glass ceramics containing SrF2 nanocrystals.Eu2+-Mn2+ codoped glass ceramics containing MgF2 nanocrystals and Eu2+-Tb3+ codoped glass ceramics containing SrF2 nanocrystals were prepared for the application of near UV LEDs excited red, and green phosphors materials. According to the Deter's energy transfer theory, the energy transfer between Eu2+ and Mn2+ was found to be dipole-quadrupole interactions with the maximum energy transfer efficiency about 74%. The energy transfer between Eu2+ and Tb3+ was a dipole-dipole interaction mechanism with a max energy transfer efficiency as 47%. Based on the efficient energy transfer of Eu2+→Mn2+ and Eu2+→Tb3+, it was possible that the white light could be obtained under the excitation of single wavelength.The Ce3+ and Tb3+ codoped glasses and glass ceramics containing SrF2 nanocrystals were prepared by melt quenching and subsequent heat treating. The XRD patterns and photoluminescence spectra revealed that the Ce3+ and Tb3+ ions have been incorporated into SrF2 nanocrystals. It was revealed that the energy transfer between Ce3+ and Tb3+ was dipole-dipole interactions. The emission intensity of Tb3+ ions in the glass ceramics was much stronger than that in the precursor glass. indicating more efficient energy transfer from Ce3+ to Tb3+ in the glass ceramics due to the enrichment of Ce3+ and Tb3+ ions and the shortening of the distance between Ce3+ and Tb3+ ions in the precipitated SrF2 nanocrystals. The glass ceramics could emit bright green light by adjusting concentration ratio of Ce3+ to Tb3+ and heat treatment temperature.Ce3+-Dy3+ codoped glass ceramics containing LaF3 nanocrystals were prepared for the application of UV LED excited white light phosphor. The emission intensity and CIE chromaticity coordinates of the Ce3+ and Dy3+ codoped glasses significantly changed with concentration ratio of Ce3+ to Dy3+. The emission intensity of both Ce3+ ions and Dy3+ ions in the 3.0 mol% Ce3+ and 3.0 mol% Dy3+ codoped glass ceramics increased significantly in comparison with that in the glass. In the glass ceramics, much higher energy transfer efficiency from Ce3+ to Dy3+ could be attributed to shorter distance between the rare earth ions. These glasses and glass ceramics have great potential application in white LEDs since it could emit bright white light by adjusting the concentration ratio of Ce3+ to Dy3+ and heat treatment temperature.Rare earth ions doped glass ceramics were studied to improve the efficiency of solar cells. Efficient near infrared emission of Yb3+was obtained in the Ln3+-Yb3+ codoped glass ceramics due to downconversion energy transfer from Ln3+ to Yb3+ ions. Among the Nd3+-Yb3+, Pr3+-Yb3+, Eu3+-Yb3+,Tb3+-Yb3+, and Tm3+-Yb3+pairs, the Nd3+-Yb3+ pairs had the highest infrared quantum yield nearly 200%.The infrared downconversion quantum cutting between Pr3+ and Yb3+ occurred through two step cross relaxation energy transfer with the'G4 energy level acting as the intermediate state. It could be described as:Pr3+(3P0→1G4)-Yb3+(2F7/2→2F5/2), and flllowed by Pr3+(1G4→3H4)-Yb3+(2F7/2→2F5/2). The emission intensity of Yb3+ improved largely in the glass ceramics containing SrF2 nanocrystals.Yb3+doped glass and glass ceramics containing ZnO dots sized about 8～15 nm were prepared. Intense near infrared emission around 1000 nm that originated from the transition of Yb3+:2F5/2→2F7/2 was generated as a result of energy transfer from oxygen interstitials in ZnO nano-dot to Yb3+ with an energy transfer efficiency about 10%. The quantum yield of the near infrared emission of Yb3+ under the excitation of 390 nm was about 16.7%. These materials have potential application in achieving high efficiency c-Si solar cells via spectrum modification.