Effects of Sr/Al non-stochiometry and B2O3 flux on the crystal phase evolution and long-afterglow luminescence of the SrAl2O4: Eu2+, Dy3+ phosphor.
Sr/Al 비화학양론성 및 B2O3 융제 첨가량이 SrAl2O4: Eu2+, Dy3+ 축광체의 결정상 및 축광 성능에 미치는 영향.
- 주제(키워드) Effects of Sr/Al non-stochiometry and B2O3 flux on the crystal phase evolution and long-afterglow luminescence of the SrAl2O4: Eu2+ , Dy3+ phosphor.
- 발행기관 강릉원주대학교 일반대학원
- 지도교수 신현호
- 발행년도 2015
- 학위수여년월 2015. 2
- 학위명 박사
- 학과 및 전공 일반대학원 재료공학과
- 원문페이지 xxxviii, 188
- 실제URI http://www.dcollection.net/handler/kangnung/000000006865
- 본문언어 영어
초록/요약
The effects of Sr/Al non-stochiometry and B2O3 flux on the crystal phase evolution and long-afterglow luminescence of the SrAl2O4: Eu2+, Dy3+ phosphor were investigated. Through a series of investigations on (1) the effect of B2O3 amount, (2) the effect of the nominal substitution of Dy3+ for the cation sites in the host phase, (3) the effect of the dosage of the activators, (4) the effect of the [Sr]/[Al] ratio of the host phase, (5) the effect of the addition of the alkaline ions, the best long-afterglow luminescence was achieved when (1) Dy3+ nominally substituted for the Al site, (2) the dosage of the activators was 0.04Eu2+ and 0.04Dy3+, and (3) the amount of the B2O3 flux was 0.3 mole (per moe of the host phase): Sr0.96Al1.96O4: 0.04Eu, 0.04Dy + 0.3B2O3 (0.35 cdm-2 at 10 min data). In the process of seeking the correlation between the quantified amount of the crystalline phases and the long-afterglow luminescence, it was analyzed that: (1) the actually incorporated quantity of activators is very small as compared to the nominally added quantity in the starting batch (the actually required quantity of Dy is even smaller than Eu); (2) the governing parameter of the LAG performance is not the incorporation of Eu to the main host phase (related to enhanced PL excitation and emission) but rather the incorporation of Dy (related to the enhanced charge storage in a richer thermal trap), and; (3) the LAG performance is not governed simply by the quantity of the main luminescent host but rather by the quality of the main host (i.e. efficient incorporation of Dy into the host). As a criterion for the efficient incorporation of Dy to the main host, it was deduced that if the number of Al available for the formation of the main host was less than the stoichiometric value of 2 with reference to the number of the Sr lattice site in the main host, i.e., =[Al]/[Sr+Eu+Dy+VSr] < 2, boron would suitably join the [Al,B]O4 structural unit. The enhanced Dy incorporation due to the active boron incorporation was interpreted to yield the high-quality main host, demonstrating the superior LAG performance despite the sacrifice of the main host in the case of Al-site nominal substitution. It was shown that the value calculated simply from the starting batch itself may serve as a practical parameter to control the LAG performance within a given composition series, provided that the types of secondary phases and glass composition are not significantly different in the composition series. Briefing each chapters, chapter one gives a brief and general background of phosphor materials, mechanisms for the underlined phosphors, apparatus, methodology utilized for the synthesis and analysis of the strontium aluminate phosphors. The chapter focuses on solid state reaction route which was employed throughout this work. Chapter two presents an overview of persistent luminescence phosphors as well as the role lanthanides play in such phosphors. Then, an in-depth analysis of the mechanisms of persistent luminescence is provided. Chapter three describes the optimal effect of applied B2O3 variation on the excess addition and nominal substitution of Dy3+ to Sr and Al sites in SrAl2O4: 0.04Eu2+ phosphors. At 10 min data, the maximal long-afterglow luminescence was found at x = 0.3 with slightly decrease at x = 0.4 for all of the three series. The quantified results of the phases by rietveld refinement show that the quantity of SrAl2O4 main phase increases up to x = 0.3, while the quantity of non-luminescent phases like AlDyO3, Dy3Al5O12, Dy4Al2O4, and EuSrAl3O7 degrade for the excess addition and Al-site series. Where for the Sr-site series, the quantity of the SrAl2O4 decrease up to x = 0.2 but afterwards it increase from x = 0.3, which explain the increase in LAG luminescence up to x = 0.3. While the decrease in quantity of SrAl2O4 main phase is compensate by another luminescent phase i.e., Sr4Al14O25 at x = 0.4 for the excess addition and Al-site series, while for the Sr-site series it compensate the main phase from x = 0 ~ 0.4. These quantified results are well correlated with the increase in LAG luminescence, however, through the comparison of the PL excitation/emission with LAG luminescence, not only the quantity of luminescence phase but also the quality of luminescence phase co-operate with Dy3+ incorporation at x = 0.3, are interpreted to govern the LAG luminescence. Chapter four focuses on the effect of Dy3+ substitution to SrAl2O4: 0.04Eu2+, xDy3+, where x = 0.02, 0.04, 0.06, by three series: (1) excess addition, (2) Sr-site nominal substitution, and (3) Al-site nominal substitution, under the condition of fixed B2O3 addition (0.3 mol). SrAl2O4: Eu2+, Dy3+ long-afterglow (LAG) phosphors with nominal substitution of Dy for Al site demonstrated superior performance as compared to the cases of nominal substitution for the Sr site or excess addition, despite the fact that a reduced quantity of the SrAl2O4 main host phase existed when Dy3+ was nominally substituted for Al. It was deduced that if the number of Al available for the formation of the main host was less than the stoichiometric value of 2 with reference to the number of Sr lattice site in the main host, boron would suitably join the [Al,B]O4 structural unit, yielding an improved incorporation of Dy3+ to the SrAl2O4 main host which, in turn, improves the LAG luminescence. Chapter five reports a brief results of Eu2+/Dy3+ effect on Sr1-xAl2-yO4: xEu, yDy –0.3B2O3 series. Where for x = y = 0.04 shows the superior LAG luminescence intensity, while the crystal structure found different and only two phases SrAl12O19 and Sr4Al14O25 were noted. Chapter six is about the effect of Al/Sr series, i.e., SrAlxO4: 0.04Eu, 0.04Dy (x = 1.84, 1.88, …., 2.16). The intensity of PL excitation/emission spectra increases as Al content increases up to x = 2 with a stable 368 nm and 522 nm respectively, while above this there is decrease but variant trend of intensity. The specimen with x = 2 among the series shows the superior intensity of LAG luminescence and maintain the duration of 1 h. The quantified results of Rietveld refinement of XRD patterns also correlate that the dominant SrAl2O4 phase quantity increases up to x = 2, which explains the increase in LAG luminescence up to x = 2. It was also shown by the calculated value explained above from the starting batch itself may serve as a practical parameter to control the LAG performance within a given composition series. Chapter seven describes a series of SrAl2O4: Eu2+, Dy3+ long-afterglow phosphors with varying concentration of Li+, Na+ and K+, has been synthesized. As the concentration of each type of alkaline ion increases up to 4 mol%, the quantity of the main SrAl2O4 host phase generally decreases by forming glass phase or secondary phases, which results in a decreased PL excitation/emission, and decreased afterglow performance. The type of defect complex formed by the addition of an alkaline ion has been deduced and compared with that formed when no alkaline ion is added. Keywords: SrAl2O4, Oxide materials, Solid state reaction, Luminescence, Long after-glow phosphors, Alkaline ions, Defect complex, Optical properties.
more목차
Table of Contents
Chapter 1. General Introduction
1.1. The terminology and definition of phosphor
1.2. Fundamental of luminescence
1.3. Long After-glow Phosphors
1.3.1. Mechanism of the long persistent phosphorescence
1.3.2. Methods to design Long Persistent Phosphor
1.3.3. Experimental Techniques of Measuring in Long Persistent Phosphors
1.3.4. Methods of Preparation of Long Persistent Phosphors
1.4. Summary and objectives of the study
References
Chapter 2. Literature Review
References
Chapter 3. Optimal effect of B2O3 on the excess addition and nominal substitution of Dy3+ to Sr and Al sites in SrAl2O4: 0.04Eu2+ phosphors
3.1. Introduction
3.2. Experimental
3.3. Results
3.4. Discussions
3.4. Conclusion
Acknowledgments
Chapter 4. Effect of nominal substitution of Dy3+ for host cations in SrAl2O4: Eu2+ phosphor on phase evolution and long afterglow luminescenc
4.1. Introduction
4.2. Experimental Procedure
4.3. Data and Results
4.4. Discussion
4.4.1 Crystal phase evolution and Dy incorporation into the host
4.4.2 Afterglow property in terms of Sr site occupancy by Dy
4.4.3 Afterglow property in terms of the [Al]/[Sr] ratio of the starting batch
4.5. Conclusions
Acknowledgments
References
Chapter 5. The effect of Eu2+/Dy3+ substitution on the afterglow property of SrAl2O4 phosphor with a fixed 0.3 mole of B2O3
5.1. Introduction
5.2. Experimental
5.3. Results
5.4. Conclusions
Acknowledgments
References
Chapter 6. Effect of Al/Sr ratio on SrAlxO4: 0.04Eu, 0.04Dy -0.3B2O3 phosphors
6.1. Introduction
6.2. Experimental Procedure
6.3. Results
6.4. Conclusions
Acknowledgments
References
Chapter 7. Effect of alkaline ions on the phase evolution, photoluminescence, and afterglow properties of SrAl2O4: Eu2+, Dy3+ phosphor
7.1 Introduction
7.2 Experimental
7.3 Results and discussion
7.3.1 Effects of alkaline ions on the phase evolution, PL, and LAG property
7.3.2 Defects formed by the incorporation of the alkaline ions.
7.4 Conclusion
Acknowledgments
References
Chapter 8. General conclusion
8.1 Conclusion
