SUNLIGHT-EXCITED INFRARED LONG PERSISTENCE OF 2+ 3+ 3+ 3+ SRAL2O4: EU , DY , ER / ND NANOPHOSPHORS by NAIYIN YU (Under the Direction of Zhengwei Pan) ABSTRACT Strontium aluminate co-doped with divalent europium, trivalent dysprosium ions 2+ 3+ (SrAl2O4: Eu , Dy ) shows a green demonstrated long persistence lasting for up to 15 hours under sunlight excitation. The research presented in this thesis focus on the Er3+/ Nd3+ activated 2+ infrared (IR) long persistence due to the persistent energy transfer process in SrAl2O4: Eu , Dy3+, Er3+/ Nd3+ nanophosphor system. The XRD, SEM, EDX and optical spectra analysis method are employed to characterize the phosphors synthesized by combustion route. The 2+ 3+ 3+ efficient energy transfer process from sensitizer Eu to the activator Er / Nd in SrAl2O4 host system is investigated. Meanwhile, the long persistence luminescence in IR region is obtained. To our knowledge, there is no related material system regarding sunlight-excited infrared long persistence nanophosphor reported. 2+ 3+ 3+ 3+ INDEX WORDS: SrAl2O4: Eu , Dy , Er / Nd , Infrared (IR) long persistence, Persistent energy transfer SUNLIGHT-EXCITED INFRARED LONG PERSISTENCE OF 2+ 3+ 3+ 3+ SRAL2O4: EU , DY , ER / ND NANOPHOSPHORS by NAIYIN YU B.S., Shanghai Jiao Tong University, China, 2006 A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE ATHENS, GEORGIA 2008 © 2008 NAIYIN YU All Rights Reserved SUNLIGHT-EXCITED INFRARED LONG PERSISTENCE OF 2+ 3+ 3+ 3+ SRAL2O4: EU , DY , ER / ND NANOPHOSPHORS by NAIYIN YU Major Professor: Zhengwei Pan Committee: Loris Magnani Heinz-Bernd Schüttler Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia August 2008 iv ACKNOWLEDGEMENTS Thanks to Dr. Zhengwei Pan who gave me all the support and inspiration to finish this thesis. Thanks to Dr. Loris Magnani and Dr. Heinz-Bernd Schüttler who served as my committee members. Thanks also to all the other group members, Yiying Lu, Yanjun Chuang and especially Dr. Feng Liu and Dr. Zhanjun Gu for their support during my two years research. v TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ........................................................................................................ⅳ LIST OF TABLES.....................................................................................................................ⅶ LIST OF FIGURES.................................................................................................................. ⅷ CHAPTER 1 INTRODUCTION........................................................................................................... 1 REFERENCES .......................................................................................................... 3 2 BACKGROUND REVIEW............................................................................................... 4 2.1 LONG PERSISTENT PHOSPHOR........................................................................... 4 2+ 3+ 2.2 MECHANISMS FOR THE PHOSPHORESCENCE OF SRAL2O4: EU , DY ................ 5 2.3 RARE EARTH ELEMENTS .................................................................................. 8 2.4 ENERGY TRANSFER IN INORGANIC SYSTEM BETWEEN RE IONS ....................... 10 REFERENCES ........................................................................................................ 11 3 SYNTHESIS AND CHARACTERIZATION OF SRAL2O4 HOST NANOPHOSPHORS ............... 12 3.1 PREPARATION OF RE-DOPED SRAL2O4 NANOPHOSPHORS ................................ 12 3.2 CHARACTERIZATION METHODS ...................................................................... 14 REFERENCES ........................................................................................................ 17 2+ 2+ 3+ 4 SRAL2O4: EU AND SRAL2O4: EU , DY OPTICAL PROPERTIES AND LONG PERSISTENCE PHENOMENON................................................................................. 18 4.1 STRUCTURE OF SRAL2O4 SYNTHESIZED BY COMBUSTION METHOD ................. 18 vi 2+ 2+ 3+ 4.2 OPTICAL SPECTRA ANALYSIS OF SRAL2O4: EU / EU , DY SYSTEM ............ 24 2+ 3+ 4.3 LONG PERSISTENCE LUMINESCENCE IN SRAL2O4: EU / DY NANOPHOSPHORS ........................................................................................... 30 4.4 CONCLUSIONS ................................................................................................ 34 REFERENCES ........................................................................................................ 35 2+ 3+ 3+ 3+ 5 IR LONG PERSISTENCE IN SRAL2O4: EU , DY , ER / ND NANOPHOSPHORS THROUGH PERSISTENT ENERGY TRANSFER ............................................................ 36 2+ 3+ 5.1 ENERGY TRANSFER BETWEEN EU AND ER IONS IN SRAL2O4....................... 36 2+ 3+ 3+ 5.2 IR LONG PERSISTENCE IN SRAL2O4: EU , DY , ER NANOPHOSPHOR .......... 41 2+ 3+ 3+ 5.3 IR LONG PERSISTENCE IN SRAL2O4: EU , DY , ND NANOPHOSPHOR THROUGH ENERGY TRANSFER ........................................................................ 42 5.4 METHODS FOR LONG PERSISTENCE PROPERTIES IMPROVEMENT ...................... 45 5.5 CONCLUSIONS ................................................................................................ 48 REFERENCES ........................................................................................................ 50 6 CONCLUSIONS .......................................................................................................... 51 vii LIST OF TABLES Page Table 4.1: Unit cell parameters for SrAl2O4 nanocrystallince .................................................... 20 2+ 3+ Table 4.2: Decay times of SrAl2O4: 0.8 % Eu , x % Dy Nanophosphors ............................... 33 2+ 3+ 3+ Table 5.1: Decay times of SrAl2O4: 0.8 % Eu , 1.0 % Dy , x % Er Nanophosphors at 1530 nm..................................................................................................................... 42 viii LIST OF FIGURES Page 2+ Figure 4.1: (a) XRD pattern of SrAl2O4: Eu ; (b) Standard SrAl2O4 XRD, JCPDS No. 34-379 ………………………………………………………………………………………...19 Figure 4.2: SEM images of SrAl2O4 with the magnifications of 15000 (a) and 30000 (b).......... 21 Figure 4.3: EDX spectra of SrAl2O4, (a) whole SEM image with a magnification of 60000, (b) EDX energy spectra, (c) SrK, (d) AlL, (e) OK, (f) EuM energy distributions ................ 22 2+ Figure 4.4: (a) Absorption and excitation spectra from SrAl2O4: Eu nanophosphor, (b) 2+ 3+ Absorption and excitation spectra from SrAl2O4: Eu , Dy nanophosphor .............. 23 2+ Figure 4.5: The influence of emission intensities from various Eu concentrations in SrAl2O4 host nanophosphors, λex = 350 nm. Inset is the relation between the 515 nm emission intensities and Eu2+ concentrations. ........................................................................... 25 2+ Figure 4.6: Excitation (Exc.) and emission (Em.) spectra of SrAl2O4: Eu nanophosphors at 77 K (a) and 300 K (b).............................................................................................. 26 Figure 4.7: Synchronous emission spectra and schematic energy levels diagram at 77 K from 2+ SrAl2O4: Eu nanophosphor..................................................................................... 29 2+ 2+ 3+ Figure 4.8: Excitation (Exc.) and emission (Em.) spectra of SrAl2O4: Eu / Eu , Dy nanophosphors.......................................................................................................... 31 2+ 3+ Figure 4.9: Decay curves of green long persistence from SrAl2O4: Eu , Dy nanophosphors .. 32 2+ 2+ Figure 5.1: 1530 nm IR excitation (Exc.) and emission (Em.) spectra from SrAl2O4: Eu / Eu , Er3+ nanophosphors................................................................................................... 37 ix 2+ 3+ Figure 5.2: Schematic diagram of energy transfer between Eu and Er ions in SrAl2O4 nanophosphors.......................................................................................................... 39 2+ 3+ Figure 5.3: 1530 nm IR excitation (Exc.) and emission (Em.) spectra of SrAl2O4: Eu , Er nanophosphors, Exc. and Em. are normalized at 519 nm........................................... 40 Figure 5.4: Schematic energy level diagram and optical spectra of Nd3+ ion.............................. 43 2+ Figure 5.5: 1059 nm IR excitation (Exc.) and emission (Em.) spectra from SrAl2O4: 0.8% Eu , 1.0% Dy3+, x% Nd3+ nanophosphors, Exc. and Em. are normalized at 582 nm .......... 44 2+ 3+ Figure 5.6: 1530 nm IR excitation (Exc.) and emission (Em.) spectra from SrAl2O4: Eu , Dy , 3+ Er nanophosphors additive with various amount of H3BO3 ..................................... 46 Figure 5.7: XRD patterns of (a) 20 % H3BO3 additive SrAl2O4 nanophosphor, (b) 800˚C produced SrAl2O4 nanophosphor............................................................................... 47 Figure 5.8: 1530 nm IR excitation (Exc.) and emission (Em.) spectra of SrAl2O4 Nanophosphors produced from different ignition temperatures........................................................... 49 CHAPTER 1 INTRODUCTION 2+ 3+ Green long persistent phosphor strontium aluminate, SrAl2O4 activated by Eu , Dy ions have long been of interest for its high quantum efficiency, long afterglow without radiation and good chemical stability [1, 2]. Up to now many efforts have been made on the study of infrared (IR) long persistence of SrAl2O4 host phosphor, while little extension is investigated. As we known, Er3+