Effects Of High Magnetic Field And Two-wavelength Excitation On The Luminescence Properties Of Rare-earth-doped Glass-ceramics

Functional materials with both magnetic and optical properties have sparked considerable interest due to their potential applications in new magneto-optical multifunctional devices. Efficient broadband excited NIR to visible up-conversion for rare-earth ions can be achieved by two-wavelength excitation, which will be of great interest owing to their potential applications in solar cells. In this thesis, the effect of high pulsed magnetic field and two-wavelength excitation on the photoluminescence of rare-earth-doped nano-glass-ceramics has been investigated. We analyzed the observed phenomena and discussed the relevant mechanisms. This research includes these following topics:1. The effect of high magnetic field on the photoluminescence (PL) of Eu3+-doped nano-glass-ceramics. Eu3+-doped glass ceramics containing SrF2 nanocrystals have been successfully made by the conventional melt-quenching process and following heat treatment process. The dependence of the PL intensities of the Eu3+-doped glass ceramic on the magnetic field (0-42 T) at 77 K has been studied. We found that, the PL integrated intensities of Eu3+ ions excited by 392 nm laser are reduced with the increase in the strength of magnetic field. From a detailed analysis, we found that the integrated PL intensities of transitions from 5D0→7F1,5D0→7F2 and 5D0→7F4 all decrease with the enhancement of magnetic field. This result can be ascribed to the cooperation effect of the Zeeman splitting of Eu3+ ions. In addition, magnetic field splits 4f levels of RE ions due to Zeeman effect and this effect becomes prominent at higher magnetic field. The peaks of the Do— F4 transition of Eu 了 ions show clear blue shift at higher energy side and red shift at lower energy side. The functional materials we prepared can serve as a good optical-magnetic dual-functional materialfor various potential applications.2.The PL hysteresis behavior of Eu3+-doped glass ceramics induced by magnetic field. Eu2+-doped glass ceramics containing SrF2 or nanocrystals have been successfully made by the conventional melt-quenching and the following heat treatment process. The dependence of the PL of Eu2+-doped glass and glass ceramics on the magnetic field (0 ?39 T) at 80 K have been studied. We found that, on therising side of magnetic field, the integrated PL intensities of Eu〕十 ions decrease withthe increase of magnetic field; on the falling side of magnetic field, the integrated PL intensities of Eu2+ ions increase with the decrease of magnetic field. When the magnetic field decreases to 0 T, however, the integrated PL intensity is greater than the original value (without magnetic field). We believe the magnetization of Eu3+ ions under the magnetic field contribute to this PL hysteresis behavior. The functional materials we prepared are expected to be applied to develop new magneto-optical multifunctional devices.3. The effect of two-wavelength excitation on the photoluminescence of Ho3+ -doped glass ceramics. The influence of two-wavelength excitation and single-wavelength excitation on the photoluminescence of Ho3+-doped glass ceramics has been studied. We found that, when excited by a single 980 nm or 1150 nm laser, the PL intensities of Ho3+are quite weak and can hardly be detected. In contrast, when excited by 980 nm and 1150 nm simultaneously, the visible up-conversion emission intensity is greatly enhanced, showing strong red emission and weak green emission. We ascribe this enhancement of PL to the energy transfer up-conversion mechanism which is the most efficient of the various two-photon up-conversion processes. In addition, with the increase of Ho3+-doping concentration, the emission intensity of 5F5→5I8 transition goes down and the peak center of this transition shifts to lower energy side. In conclusion, the material we studied has efficient broadband excited up-conversion emission and may find potential application in solar cells.