Luminescence Dynamics of Eu2+ in LiBaF3 Crystals
- Abstract
- Pure and Eu2+ doped LiBaF3 single crystals have been grown by the Czochralski method. The detailed preparation procedure of crystal growth has been investigated. The melting point of LiBaF3 powder has been analyzed by the DTA measurement. The lattice parameters and phase identification have been measured by XRD. It has been confirmed that the different mole ratios of LiF:BaF2 powder and calcinations times can greatly influence the purity of LiBaF3 compounds. The substitution mechanism of Eu2+ ion has been discussed, and the Ba2+ site is reasonable in LiBaF3 crystal.
The absorption and excitation spectra show two band peaks due to the splitting of 5d states. The high resolution emission spectra show a line emission near 359 nm from 4f’ → 4f transition and a band emission maximum at 410 nm from the 5d → 4f transition. The zero-phonon line of the 4f’ → 4f transition is observed with some Stokes and anti-Stokes vibrations, and their intensity shows strong temperature dependence. The luminescent decays of line and band emissions monitoring at 359 and 410 nm have been measured in the temperature range from 15 to 300 K. The decay of band emission at 410 nm has two components: fast (~ μs) and slow (~ms) components. A three-level model of Eu2+ in LiBaF3 host was successfully built, and the energy barriers and transition rates of the excited 4f and 5d states were obtained by using the thermal quenching and three-level models, respectively.
The initial and integrated emission intensities, temperature-dependent decay values, rise times and non-exponential decay curves of line and band emissions show a quantum tunneling process resulting in unusual energy back transfer from the excited 4f to 5d states at low temperature. The luminescence dynamics of LiBaF3:Eu2+ from 15 to 300 K have been well discussed. The anomalous relaxation process is caused by the energy transfer and back transfer processes between 4f to 5d states assigned to competition of the thermal activated and quantum tunneling effects.
- Issued Date
- 2011
- Awarded Date
- 2011. 8
- Type
- Dissertation
- Publisher
- Pukyong National University
- Department
- 대학원 물리학과
- Advisor
- Seo Hyo Jin
- Table Of Contents
- 1. Introduction 1
2. Background of crystal growth and luminescence dynamics 5
2.1 Crystal growth by the Czochralski method 5
2.2 Crystal structure of ABF3 type fluorides 9
2.3 Site-occupation of RE ions in ABF3 lattices 12
2.4 Radiative and nonradiative transitions 16
2.5 Energy levels and excited states of Eu2+ ions in solid 19
2.6 Relaxation process of excited states in a three-level system 22
2.7 Mixing of Eu2+ 4f (6P7/2) and 5d (Eg) states by tunnelling process 25
3. Experimental procedure 28
3.1 Preparation of single crystals 28
3.1.1 Synthesis procedure of LiBaF3 powder 30
3.1.2 X-ray diffraction analysis 35
3.1.3 Growth of LiBaF3 single crystals 36
3.2 Spectroscopic measurements 39
3.2.1 Measurements of absorption spectrum 39
3.2.2 Luminescence excitation and emission spectra 41
3.2.3 Luminescence spectra and decay measurements by the pulsed laser excitation 43
4. Results and discussion 45
4.1 Growth of LiBaF3:Eu2+ single crystals 45
4.1.1 Different degrees of calcinations 45
4.1.2 Results of different ratios of the LiF and BaF2 powders 48
4.1.3 The initial temperature cooling rate 50
4.1.4 Rotation and pulling speeds 51
4.2 Energy level structure of LiBaF3:Eu2+ single crystal 52
4.2.1 Absorption and excitation spectra of Eu2+ in LiBaF3 52
4.2.2 Emission spectra of Eu2+ in LiBaF3 55
4.3 Zero-phonon lines and phonon side bands of the 6P7/2 8S7/2 transition 58
4.4 Relaxation process of excited states of Eu2+ in LiBaF3 66
4.4.1 Thermal activation and quenching of the excited 4f (6P7/2) and 5d (Eg) states in LiBaF3 66
4.4.2 Calculations of energy barriers E1 and E2 84
4.5 Quantum tunneling process in double wells of the 4f (6P7/2) and 5d (Eg) states of Eu2+ in LiBaF3 92
4.5.1 410-nm slow component by tunneling process 92
4.5.2 Anomalous spectral feature and nonexponential decay curves of 410-nm slow component 101
5. Conclusions 105
6. References 108
7. Publication 112
8. Acknowledgement 116
- Degree
- Doctor
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