Rozprawy doktorskie na temat „Rare-earth doped phosphors”

Photovoltaic solar cells can generate electricity directly from sunlight without emitting harmful greenhouse gases. This makes them ideal candidates as large scale future energy producers for the global energy economy. Ideally, solar cells should be efficient and inexpensive to compete in the global energy market. Unfortunately, a number of fundamental limitations exist for the efficiency due to fundamental loss mechanisms of the semiconductor materials used to make solar cells. One of the dominant loss mechanisms from a conventional silicon solar cell is the transparency of sub-bandgap near-infrared photons. Up-conversion is an optical process involving the sequential absorption of lower energy photons followed by luminescence of a higher energy photon. This mechanism could be exploited to minimise photovoltaic sub-bandgap losses. Rare-earth doped materials have ideal up-conversion luminescent properties and have been utilised for many near-infrared to visible applications. This thesis investigates the near-infrared to near-infrared up-conversion processes required for the sub-bandgap photon utilisation within a silicon photovoltaic device. Various sodium yttrium fluoride phosphors doped with rare-earths were characterised theoretically and experimentally. Erbium doped phosphors were found to be ideal for single wavelength power dependent investigations for the non-linear up-conversion processes. The radiative and non-radiative rates of various erbium doped sodium yttrium fluoride phosphors have been approximated and compared with experimental photoluminescence results. These phosphors have been applied to the rear of a bi-facial silicon solar cell and an enhancement in the near-infrared region has been demonstrated. An external quantum efficiency close to 3.4% was measured at 1523nm under 6mW laser excitation. The non-linear dependence on incident pump power has been investigated along with the dominant up-conversion mechanisms involved. It can be concluded that up-conversion phosphors can enhance the near-infrared spectral response of a silicon device. These phosphors have high luminescent efficiencies once up-conversion occurs, but suffer from poor infrared absorption and low up-conversion efficiencies. The results from this study show that relatively high doping levels of selected rare-earths into low phonon energy crystals can improve the absorption and luminescent properties of the phosphor.

Kyoto University (京都大学)
0048
新制・課程博士
博士(人間・環境学)
甲第17670号
人博第637号
新制||人||153(附属図書館)
24||人博||637(吉田南総合図書館)
30436
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 田部 勢津久, 教授 杉山 雅人, 教授 加藤 立久
学位規則第4条第1項該当

Kyoto University (京都大学)
0048
新制・課程博士
博士(人間・環境学)
甲第18380号
人博第693号
新制||人||166(附属図書館)
25||人博||693(吉田南総合図書館)
31238
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 田部 勢津久, 教授 加藤 立久, 教授 杉山 雅人, 教授 森本 芳則, 教授 山本 行男
学位規則第4条第1項該当

The work in this thesis had two main aims. The first aim was to study the use of a number of precipitation methods to control the size and morphology of precursor phosphor materials for potential applications in a new generation of high definition and field emission displays. The morphological and luminescent characteristics of these precursor phosphor materials were studied after they were annealed to form their respective luminescent oxides using electron microscopy and light measuring techniques. The first set of experiments presented describes the development of a range of spherical submicron europium-doped yttrium oxide phosphor particles and their optimisation for use in the aforementioned applications. A homogeneous precipitation technique exploiting a hydrothermal decomposition of urea that provides hydroxycarbonate phosphor precursor ligands is at the centre of this work. In the presence of rare earth element nitrates the hydroxycarbonate ligands form spherical phosphor precursor particles that after annealing yield the luminescent oxides. This is followed by the presentation of a novel synthetic method using a micellar phase of rare earth element chlorides, after annealing, yielding europium-doped yttrium oxide. This method produces a variety of morphologies with crystallites as small as a few nanometres and up to hundreds of nanometres. Next is described a new precipitation method using ammonia and carbon dioxide gases that are introduced in a controlled manner into a solution of rare earth element chlorides at room temperature. Rare earth element hydroxycarbonates rapidly precipitate upon supersaturation, yielding a range of morphologies and particles sizes. The second aim of the thesis was to prepare a novel range of three-dimensional photonic band gap materials composed of conventional phosphor materials.

博士
國立臺灣大學
化學研究所
100
The applications of phosphors according to different excitation sources are versatile due to the utilization of rare earth ions. The tunable energy levels of 5d orbital and the large number of energy levels of 4f orbitals can emit photons with different wavelength. In this thesis, excitation sources from vacuum ultraviolet (VUV), ultraviolet (UV) to visible photons, and electrons are investigated. Emission ranges from UV to visible range and near-infrared (NIR) are also utilized. The third chapter focuses on the synthesis of red-emitting oxynitride phosphor. Intraconfigurational 4f → 4f transitions are designed because of the determined environment for 5d → 4f transitions. The high thermal stability reveals that β–SiAlON is a good candidate for white light-emitting diodes (wLEDs) and plasma display panels (PDP). Pr3+ ions show the possibility of an alternative for red emitting activators. In the fourth chapter, comparison of LED- and FED-used phosphors under electron bombardment is made and it suggests a new class of host lattice should be developed. Evidences from solid-state nuclear magnetic resonance (ssNMR) lead to a different explanation of the incorporation of rare-earth ions into AlN host lattice. A new phosphor composition of AlN doped with Si4+ and Ce3+ ions is synthesized and shows the validity for field emission displays. The fifth chapter includes two proposed quantum cutting (QC) rare-earth combination for enhancing the efficiency of crystalline silicon (c-Si)-based solar cells: (1) adding a sensitizer to transfer the excited energy to the donor with 4f → 4f transitions , and (2) using a broad band donor such as Eu2+ and Ce3+ ions. It is concluded that due to the high energy of phonons required for Ce3+ ions, Eu2+-Yb3+ pairs is a better choice.

碩士
明新科技大學
化學工程與材料科技系碩士班
107
The main lattice material of this study is carbonate，Doping the activation centers: Tb3+, Gd3+, Ce3+, respectively, to prepare red, green, and blue primary color phosphors，The synthesis method is a wet method in a solid-phase synthesis method， and is heated to 900℃and 1400℃at a temperature increase rate of 10℃per minute in a high-temperature furnace, and the calcination is carried out for 10 hours while the calcination is completed. The phosphor powder is finished and tested. The crystal structure is detected by X-ray diffraction (XRD), and the excitation and emission spectra of the phosphor are detected by photoluminescence (PL). Enter the CIE chromaticity coordinate map to know the exact color of the sample. 1.Sr2SiO4 series The sample with added Ce3+ ions has nonlinear optical blue light, and the sample with Tb3+ ions emits green light, while the addition of two rare piles of the earth (Ce3+, Tb3+) emits blue light and also has the characteristics of the above two samples. 2.Ba2SiO4 series The sample with Ce3+ ion added and calcined at 1400 °C has a nonlinear optical blue light. The sample with Tb3+ ion and calcined at 1400 °C emits green light while adding two rare piles of the earth (Ce3+, Tb3+) to emit blue light. With the characteristics of the above two samples, the same calcination temperature is also visible at 1400 °C. 3.Ca2SiO4 series When the calcination temperature is 1400 °C, the luminescence efficiency and crystallinity are better. The sample with Ce3+ has nonlinear optics and emits blue light; the sample with Tb3+ emits green light; while the sample with Ce3+ and Tb3+ remains at the same time. The characteristics of the aforementioned samples showed that the sample to which Gd3+ was added emitted red light.

碩士
國立成功大學
材料科學及工程學系碩博士班
98
Rare-earth (RE) ion doped phosphors, Li3Ba2La3-xREx(MoO4)8 (RE = Eu3+, Dy3+), were synthesized by a solid-state reaction process at 800C. The structural and photoluminescent properties of the prepared phosphors were investigated by X-ray diffraction, scanning electron microscopy, Raman scatter spectroscopy, UV-visible absorption, and photoluminescence (PL) spectroscopy. The aim of the research was to develop novel phosphors for the UV-LED to white light conversions. The experimental results showed that the dominant emissions of the Li3Ba2La3-xEux(MoO4)8 phosphors under the UV excitation (394 nm) were at 593 nm and 618 nm, originating from the electronic transitions between the trivalent RE states. Due to the high phonon frequency of the host lattice, the transitions from the emitting levels higher than 5D0 were not observed in the PL spectra. The above two observed emissions were due to the 5D0-＞7F1 (593 nm) and 5D0-＞7F2 (618 nm) transitions. In particular, the 5D0-＞7F2 emission was very strong and for the x=2.1 samples, its peak intensity was about 3.3 times more than the commercial phosphors ZnS:(Mn2+,Te2+). The CIE chromaticity coordinate of the Li3Ba2La0.9Eu2.1(MoO4)8 red emissions was calculated to be at (0.67, 0.33), which is almost the same as the standard red chromaticity of the NTSC system. In the Li3Ba2La3-xDyx(MoO4)8 (x=0.01-0.24) series, the dominant emissions under the UV excitation (388 nm) were from the 4F9/2-＞6H15/2 (blue) and 4F9/2-＞6H13/2 (yellow) transitions, and the intensity of the later was stronger. The mixture of all the emissions had the CIE chromaticity coordinates at (0.35, 0.40), which is at the yellowish-white color region.

The research endeavor on the yttrium borate (YBO3) phosphors for an array of applications, including light emitting diodes, flat display technology and optoelectronic devices, is escalating with the availability of these borate hosts, which present incentives such as excellent UV absorbance, high thermal and chemical stability and exceptional optical damage threshold. An insight into their inherent potential necessitates the requirement for a meticulous investigation of their photoluminescence properties, especially with respect to the type of dopant used. However, for the preparation of this aforementioned host, the use of boric acid (H3BO3) as a boron source is widely prevalent. The literature gives a plethora of evidences for the difficulties encountered in formation of a phase pure YBO3 on higher temperatures. Apart from that, the most critical parameter of Y:B ratio has a crucial effect on the phase purity of the material. The key objective of this research work is to synthesize yttrium borate (YBO3) host matrix as well as single rare earth doped and co-doped YBO3 phosphors using novel sodium borohydride based solution precursor route, while probing their photoluminescence behavior by varying different parameters emphasizing color tunability including white light for versatile application domains. In this thesis we report a novel borohydride synthesis route based on the inclusion of sodium borohydride, which acts both as a boron source and as a precipitating agent, at room temperature without any organic additives, for the successful synthesis of yttrium borate based phosphors. New experimental approach has been demonstrated to form phase pure material, which eliminates the addition of any external precipitating agent, with a detailed emission characteristics analysis for the development of single activator Eu-doped YBO3 and Tb-doped YBO3 phosphors. In addition, color tuning in case of single activator doped YBO3 [Eu-doped and Tb doped] was demonstrated with a focused approach of excitation wavelength induced photoluminescence for samples calcined at 800 °C and 1200 °C. The evaluated chromaticity coordinates (CIE) derived from the spectral energy distribution of emission showed a variation with excitation wavelengths, thereby validating the excitation wavelength dependent tunability of a single activator doped YBO3 phosphors. Besides, incredibly distinguishable colors on irradiating the phosphors by switching the standard excitation wavelengths of 254 nm and 365 nm while generating self-adjustable emissions comprising shades of red and pink for Eu-doped YBO3 and tunable shades of green from single activator Tb-doped YBO3 including near white light enriches the contribution of this research. Furthermore, single phase white light emitting phosphor by co-doping Eu and Tb ions into YBO3 matrix have been developed by this novel route, which also expounds the versatility of the borohydride method for providing different instances of phosphor materials. Again, photoluminescence studies revealed excitation induced tunable emissions in Eu, Tb co-doped phosphors with tunability spanning across yellow, neutral white, pink and red. Moreover, the properties of single activator doped and co-doped YBO3 phosphors thus developed by borohydride route have been comparatively assessed with bulk phosphor prepared by conventional solid state route. The follow up of the properties unanimously depicts that the use of sodium borohydride is virtuous for synthesizing nanophosphors. Finally, a step forward has been taken towards successfully demonstrating substantiative end-product prototype applications using the phosphor materials prepared in this research work. These include demonstration of a stable white light using blue LED in combination with an optimized single phase YBO3:Eu,Tb phosphor; developing for the first time a novel polyvinylidene fluoride [PVDF] polymer based flexible film which gives homogeneous luminescence when incorporated by the YBO3 based phosphor particles and irradiated under UV radiation of 254 nm; and a patterned film that can be practically applied and tailored further according to specific needs employed in security domain for fraud prevention. This adds another facet to the useful dimensions of applicability pertaining to YBO3 based phosphors.

碩士
國立交通大學
應用化學系分子科學碩博士班
100
Fluorosulfide and oxyfluorosulfide-based phosphors have relatively low synthetic temperature and appropriate excitation wavelengths for applications in fabricating white-light LEDs. To enhance the thermal stability of sulfides, we choose the fluorosulfides and oxyfluorosulfide as host matrices and activated with Ce3+ and Eu2+ as activator, respectively. In this study, we have prepared five series of fluorosulfide and oxyfluorosulfide phosphors, viz., Y3S2OF3:Ce3+, La2MF4S2:Ce3+ and La2MF4S2:Eu2+(M = Ca, Sr) using sealed quartz tube at 850-1000℃and 1150℃, respectively. These phosphors can be excited by radiation with wavelength ranging from 300 nm to 500 nm and their emission colors almost cover the whole visible spectral range. The content of this thesis can be divided into two parts. Firstly, we will introduce the background knowledge of phosphors used in LEDs, and then elaborate the design rules, the motivations and goals of the study. The synthetic methods and further characterization results will be discussed in the second part.

碩士
國立成功大學
材料科學及工程學系碩博士班
97
The objet of this study is to synthesize Li3Ba2Gd3(MoO4)8 doped with various activators(Eu3+,Tb3+,Dy3+,Er3+,Sm3+), and the raw material had been mechanically activated by grinding in high energy vibromill followed by calcined at temperature of 900℃ for 12 h. By using XRD, SEM, PL spectra, and UV-visable spectra, the characterization of structure, morphology of powders and photo-luminescent properties of phosphors were analized. The dominant emission peaks of Li3Ba2Gd3(MoO4)8:Eu3+ phosphor are 5D0→7F1(591nm)、5D0 →7F2(614nm) which are originate from intra-4f transitions of excited state. The intensity of the emission from 5D0 to 7F2 is stronger than 5D0 to 7F1 and three times more than commercial phosphors, ZnS:Mn2+,Te2+ when Eu3+ concentration in x=2.4. The CIE chromaticity coordinates of red emission of the Li3Ba2Gd0.6Eu2.4(MoO4)8 phosphor is (0.67, 0.33) which is just at NTSC system standard red chromaticity. There are two regions in the excitation spectra of Li3Ba2Gd2 Tb1(MoO4)8 phosphor；one is assigned from 4f��5d transition in 200 to 300 nm, and the others are from intra-4f transitions in 350 to 500 nm. The dominant emission peak of Li3Ba2Gd2Tb1(MoO4)8 phosphor is 5D4��7F5 under excitation of 307nm. The CIE chromaticity coordinates of green emission of the Li3Ba2Gd2 Tb1(MoO4)8 phosphor is (0.25, 0.58). The the other series of green phosphor is Li3Ba2Gd2.95Er0.05(MoO4)8.Because its emission peaks locates in the light of green region, it has better color rendering index than Li3Ba2Gd2 Tb1(MoO4)8. However, the valence electrons are shielded by the 5s and 5p outer electrons, the valance electrons of trivalent rare earth ions are weakly affected by ligand ions in crystals, so the features of optical spectra of the most phosphors doped with trivalent rare earth, such as Li3Ba2Gd3(MoO4)8:Dy3+ and Li3Ba2Gd3(MoO4)8:Sm3+ is similar to those expected for free ions.

博士
國立交通大學
應用化學系碩博士班
105
The thesis is divided into three parts. Firstly, the study of the blue LED-excitable cyan-emitting, green-emitting, and reddish orange-emitting thiosilicate phosphors. Secondly, the study of the blue LED-excitable cyan-emitting and reddish orange-emitting halothiosilicate phosphors. Finally, the study of the near-UV LED excitable cyan-emitting and green-emitting thiogallates. In Chapter 1, the research background and current status of sulfides and thiosilicates are introduced, and the motivations and goals of this thesis are elaborated. The literature review was focused on the fundamentals of phosphors, concentration quenching of activators, and mechanism of energy transfer of different types of phosphors. In Chapter 2, we describe the synthesis and characterization methods of the thiosilicate phosphors; BaLa2Si2S8:R (R = Ce3+ or Eu2+), CaY2Si2S8:Ce3+, La3Br(SiS4)2:R (R = Ce3+ or Eu2+), BaGa2SiS6:Eu2+, and Ba2Ga8SiS16:Eu2+. In Chapter 3, we discuss the crystal structure and spectroscopic properties of the BaLa2Si2S8:R (R = Ce3+, Eu2+), CaY2Si2S8:Ce3+, La3Br(SiS4)2:R’ (R’ = Ce3+ or Eu2+), BaGa2SiS6:Eu2+, and Ba2Ga8SiS16:Eu2+ phosphors and their LED lighting applications. In Chapter 4, the properties of the thiosilicate phosphors are summarized and the future work is discussed.

碩士
國立交通大學
應用化學系碩博士班
102
With the gradual enhancement of environmental awareness, the development of green luminescent materials has been an important issue in phosphors research. This research is attempted to synthesize and investigate new UV-emitting materials, which can be excitated by 172 nm and used for the applications of phototherapy, sterilization, and disinfection. We have explored and investigated the luminescence mechanism of four series of UV-emitting phosphors, including nine types of rare earth-doped phosphates, silicates and borates. In this study, using the vacuum ultraviolet (VUV) light source provided by National Synchrotron Radiation Research Center (NSRRC), as well as the X-ray diffraction technique and electron microscopy analysis, we have prepared and investigated UVB-emitting NaCa(Y,Gd) (PO4)2, Na2(Y,Gd)2O(BO3)2, Li6(Y,Gd)(BO3)3, Na(Y,Gd)Si2O6, NaCa (Y,Pr,Gd)(PO4)2, Li6(Y,Pr,Gd)(BO3)3 and Na(Y,Pr,Gd)Si2O6; UVC- emitting NaCa(Y,Pr)(PO4)2 and Na(Y,Pr)Si2O6. Under excitation at 172 nm, the NaCa(Y,Gd)(PO4)2, Na2(Y,Gd)2O(BO3)2, Li6(Y,Gd)(BO3)3, Na(Y,Gd)Si2O6, NaCa(Y,Pr,Gd) (PO4)2, Li6(Y,Pr,Gd)(BO3)3 and Na(Y,Pr,Gd)Si2O6 phosphors were found to give sharp UVB emission centered at 313 nm, which was attributed to the 4f7→4f7 transition of Gd3+. Under the same excitation, NaCa(Y,Pr)(PO4)2 and Na(Y,Pr)Si2O6 were found to emit UVC light, which was found to be due to the 4f15d1 →4f 2 transition of Pr3+. With the co-doping of Pr3+ as a sensitizer, NaCa(Y,Pr,Gd)(PO4)2, Li6(Y,Pr,Gd)(BO3)3, and Na(Y,Pr,Gd) Si2O6 exhibit a much stronger emission at 313 nm. The emission intensity of the UVB-emitting NaCa(Y0.8293Pr0.0007Gd0.17)(PO4)2, Li6(Y0.695Pr0.005 Gd0.3)(BO3)3 and Na(Y0.775Pr0.005 Gd0.22)Si2O6 was found to be 1.6, 5.4, and 1.4 times that of the UVB emission of the patented LaB3O6:Bi3+,Gd3+ commodity, respectively. Our investigation results indicate that the above three Pr3+/Gd3+-coactivated phosphors may have great potential for practical application in phototherapy and tanning. The luminescence performance of all types of UV radiation was found to be crucially dependent on the chemical compositions, bonding and crystal structure of the host matrix.

博士
國立成功大學
電機工程學系碩博士班
101
Our previous work [J. Am. Ceram. Soc., 93, 138 (2010)] reported a red phosphor Ca2.82(VO4)2:0.12Eu3+ which was well-excited by 465-nm blue light and was therefore a candidate for application to the phosphor-converted WLED (pc-WLED) with a blue chip (450-470 nm). On the basis of Ca2.82(VO4)2:0.12Eu3+, we sought to develop down-shifting (DS) inorganic phosphors for use in pc-WLEDs by the commonly-used solid-state reaction method, which was the main purpose of the present research. We found that substitution of not only a larger ion like Ba2+ [J. Am. Ceram. Soc., 93, 138 (2010)] but also a smaller one like Mg2+ (this research) replacing no ＞ 14.9% Ca2+ ions could enhance the integrated DS emission intensity of red phosphor Ca3(VO4)2:0.12Eu3+, indicating that both lattice expansion and contraction could decrease the site symmetry of Eu3+ in Ca3(VO4)2:0.12Eu3+ phosphor. This finding is anticipated to improve the Eu3+ emission intensity of other Eu3+-doped phosphors. To further investigate Eu3+ up-conversion (UC) behaviors, Yb3+ ion was used as a sensitizer. Interestingly, the enhanced Eu3+ emission from 5D1,2,3 states under UC excitation was observed as compared to that under DC excitation. This phenomenon led to the variation in the emission color of the optimized (Ca0.742Mg0.067)2.82(VO4)2:0.36Yb3+,0.12Eu3+ phosphor from red to near warm white as the excitation mechanism changed from DS to UC. Additionally, it was found that substitution of 3% Sr2+ replacing Ca2+ enhanced the red emission intensity of Ca2.82(VO4)2:0.12Eu3+ by 14% under 465-nm excitation. The conventional methods to determine multipolar mechanisms responsible for the energy transfer between different ions (I0/I － C plot) and alike ions (log(C/I) － logC plot) supposed hypotheses of I0/I ≫ 1 and βCθ/3 ≫ 1, respectively, where I0 and I are the emission intensity of the energy donor in the absence and presence of the acceptor; C is the sum of both energy donor and acceptor contents; θ represents the type of multipolar interactions, and β is a constant for each interaction. Compared with the conventional methods, the modified methods for investigation of the multipolar energy transfer proposed in this research demonstrated more precise and valid results. Excluding the prerequisite of I0/I ≫ 1, the concentration-dependent dipole-dipole multipolar interactions for the Sm3+ → Eu3+ energy transfer were observed for the first time based on the fitting results of (I0/I － 1) － C plots. Additionally, the Harris model was found to be an alternative way to release us from the prerequisite of βCθ/3 ≫ 1 when fitting the I/C － C plot. And a dipole-dipole multipolar interaction of 3-body type was found to be responsible for the concentration quenching of Sm3+ emission around 951 nm in the (Ca0.97Sr0.03)3(VO4)2 host.

Rare-earth doped phosphors are fascinating both from scientific and technological standpoints because of the great scope it offers for spectral tuning, enabling a large variety of applications: from simple road markers to lighting, telecommunication, biomedical application, etc. Though the intra-4f electronic transitions are parity forbidden, photoluminescence (PL) emissions from rare-earth ions is possible due to coupling with the vibrational state, mixing with wavefunctions of opposite parity, ligand orbitals, or charge transfer state of the host matrix. Consequently, the host matrix plays an important role in determining the PL emission behavior of a given rare-earth ion. Any change in the structural features of the host, induced by chemical modification, temperature, pressure, electric field, is expected to bring about a change in the PL spectrum, providing the basis of spectral tuning. However, the shielding of the 4f levels by the 5d 6s electrons nearly fixes the energy of the Stark bands of a rare-earth ion, irrespective of the ligand environment around it. In this context, spectral tuning merely involves a change in the relative intensities of the Stark bands appearing in different wavelength regions of the PL emission spectrum. The symmetry occupied by the lanthanide ion determines the extent to which the degeneracies of the 2J+1 levels are lifted for the different 2S+1Lj spectroscopic level. The lowering of the local symmetry not only affects the selection rules of intra band transition but also increases the number of Stark manifolds observed in the PL spectrum. The Eu3+ PL emission possesses a special feature called hypersensitive transition i.e. the 5D0 → 7F2 transition of Eu3+ ion is very sensitive to small changes in the local environment and/or the degree of structural heterogeneity. Eu3+ PL has, therefore, been used as a tool for investigating local symmetry in complex structures and in the quantification of the extent of crystallization during thermal annealing of structural glasses. Ferroelectric materials exhibit an intimate relationship between the state of polarization and crystal structure. The polarization state of a ferroelectric can be influenced by factors like compositional modification, electric field, stress, and temperature, which will also affect the structural state. For example, spontaneous polarization disappears on heating a ferroelectric above the Curie point, accompanied by crystal losing its centre of inversion symmetry. Similarly, hydrostatic pressure suppresses ferroelectricity due to the dominance of the repulsive short-range interaction over the long range attractive coulombic interaction. Electric field also can change the crystal symmetry in ferroelectric solid solutions exhibiting at morphotropic phase boundary compositions. Therefore, introduction of optical functionality to ferroelectrics by doping of rare-earth ions can provide opportunities for investigation of the intriguing relationship between photoluminescence (PL) tuning and external stimuli like electric field, strain, and temperature. The discovery of extraordinary piezoelectric response in BaTiO3 based piezoelectric in recent years has stimulated scientific research on the development of alternative for lead based piezoceramics. Generally, the piezoelectric response of the system is enhanced by tuning the composition towards morphotropic/polymorphic phase boundary (MPB/PPB), which separates two ferroelectric phases in the composition temperature phase diagram. Recently alternate strategy has been proposed to achieve superior piezoelectric performance by introduction of local structural distortions to manipulate interfacial energies. Observing the influence of local structural heterogeneity on the piezoelectric performance, it is important to understand the effect of poling on the overall structural heterogeneity of the PPB composition. Modern day ferroelectric-based miniaturized devices require grain size to be restricted in the submicron regime, which can induce internal stress because of the deficiency of ferroelastic domains. Not only the grain size, but the processing techniques itself are also likely to introduce a great deal of strain inhomogeneity in the system. For a better appreciation of the overall performance of such ferroelectric microelectronic devices, it is important to understand how these constraints influence the structure and microstructure on the global and local length scales. Using the great sensitivity of the 5D0 → 7F2 transition of Eu3+ ion, we have studied the structural heterogeneities in case of poling effect on polymorphic phase boundary composition, inhomogeneous lattice strain, and size restricted submicron ferroelectrics. Chapter 1 of the thesis provides an introduction to the fundamental concepts related to ferroelectrics materials. An overview of lanthanide luminescence properties and advantages of Eu3+ photoluminescence as a structural probe is discussed. This is followed by the concepts associated with non-contact luminescence temperature sensing in lanthanide doped materials. The details of the experimental techniques, characterization tools used, and some theory behind these techniques have been provided in chapter 2. A high-performance piezoceramic is inherently a heterogeneous system comprising of a complex network of ferroelectric domain walls and interphase boundaries coupled within and across randomly oriented grains. Chapter 3 discusses how this heterogeneity is affected by a strong electric field in the lead free piezoelectric Ba(Ti1-xSnx)O3 (BTS) in the vicinity of polymorphic phase boundary, using rare-earth PL as a spectroscopic probe. Eu3+ ions are randomly dispersed (in dilute concentration) in the BTS matrix to make use of PL signal as a structural probe. The very high quantum yield of Eu3+ makes it possible to get very good PL intensity even with a very small concentration of Eu3+ in the dielectric matrix, thereby assuring that the probe itself does not interfere too much with the essential characteristics of the system. Detail analysis of the PL profile patterns in different structural regions show one to one correlation between Eu PL spectra (Stark bands) and global crystal structure. In case of poled specimens of PPB composition, 5D0 → 7F2 hypersensitive transition of Eu3+ shows an irreversible increase in the intensity. In contrast, XRD study in situ with electric field shows reversible P4mm →Amm2 phase transformation. This indicates an overall increase in the local low symmetric phases because of the field induced motion of inter phase boundaries. This study proves that the role of poling is not merely limited to make the ceramic piezo-active, but it also plays an important role in enhancing the performance of the MPB/PPB piezoceramic by increasing the overall local structural heterogeneity. Chapter 4 discusses about the local structural heterogeneity developed in BaTiO3 for two different important situations: (i) lattice is inhomogeneously strained and (ii) grain size restricted in the submicron regime. We make use of the great sensitivity of the hypersensitive 5D0 → 7F2 transition of Eu3+ in local crystal environment to probe the structural heterogeneity developed in BaTiO3 for the two conditions. A systematic comparative investigation was performed on the solid solutions series Ba(Ti1–xSnx)O3 with x = 0.0, 0.03, 0.06, and 0.09, doped with Eu2O3 in dilute concentration. We have deliberately introduced inhomogeneous lattice strain in well sintered grains of these compositions by subjecting them to uniaxial loading for an extended duration. XRD patterns show a significant broadening of the XRD Bragg profiles of the pressed specimens in addition to the stabilization of partial orthorhombic phase in pressed x = 0 and 0.03 compositions. PL measurements show an increase in the 5D0 → 7F2 band emission because of the pressing effect. Microstrain calculations (by Williamson-Hall method) of pressed specimens found a one-to-one correspondence between the degree of the residual microstrain and the intensity of the7F2 hypersensitive band. Similarly, Eu3+ hypersensitive band shows an increase in intensity in case of specimens with submicron size grains as compared to the specimens with above micron size grains. Although the global structure remains unchanged in BaTiO3, suggesting the system exhibits considerably large structural heterogeneity by inducing low symmetry distortions on the local scale when the size is restricted in the submicron regime. The ability to tune the PL spectrum by temperature forms the basis of optical thermometry. Compared to others, this mode of thermometry is advantageous because of the non-contact/remote mode of measurement, fast response time, and being able to operate in corrosive and other kinds of harsh environmental conditions. In conventional approach, optical thermometers are designed by using the thermally driven change in the relative intensity of a pair of Stark lines (commonly known as Fluorescence Intensity Ratio, FIR) in the photoluminescence (PL) spectrum of rare-earth doped solids. Chapter 5 discusses about new strategies to develop a highly sensitive optical thermometer wherein judicious exploitation of the temperature dependence of the Raman signal of the crystalline host, in conjunction with the temperature dependence of the photoluminescence (PL) signal of the doped rare-earth ions, can give very large sensitivity. The phenomenon is demonstrated on a Eu, Er doped BaTiO3. In our model system, Eu3+ band intensities decrease at cryogenic temperature whereas Raman band intensities increase with decreasing temperature, resulting a temperature induced change in emission color from orange to green (on cooling). Anomalous quenching of Eu PL at low temperature can be understood as a consequence of trap state mediated relaxation process, and the increase in Raman intensity correlates well with structural ordering in the rhombohedral ferroelectric phase of host BaTiO3. We introduce a new concept of "Raman-Photoluminescence Intensity Ratio (RPIR)" for the realization of very large temperature sensitivity, not possible before. The mechanism leading to the large sensitivity is explained in detail. Another example shows realization of an optical thermometer by the intensity ratio of Er and Eu PL emission doped in nonferroelectric perovskite CaTiO3. On cooling below room temperature, Er3+ band intensities increase with decreasing temperature whereas Eu3+ band intensities decrease with decreasing temperature, providing temperature dependent intensity ratio. Similarly, different rate of phonon induced PL quenching (in Er and Eu) at high temperature realizes optical temperature sensing at high temperature. The strategy discussed in this chapter offers a competitive alternative to the conventional optical thermometers to design highly sensitive non-contact thermometers with good signal discriminability. Finally, in Chapter 6, we have summarized the essential results of this thesis and also suggested prospects for further research.
Department of Science and Technology (DST)-Government of India (Inspire fellowship), Engineering Research Board (SERB) of the Ministry of Science and Technology-Government of India (Grant no. EMR/ 2016/001457)

碩士
國立交通大學
應用化學研究所
85
This research is attempted to investigate the chemical synthesis and the effects of quantity and types of rare-earth activator (R3+) doping on the structural and luminescent properties of the Y3Al5O12(YAG) phosphors. Well crystalline and x-ray pure powers of R-doped (R=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) YAG were synthesized by heat treatment of gel-precipitated precursors, first at 300℃ for 3 hours and then at 980℃ for 8 hours. The effects of sntering time and temperature on the purity of R-doped YAG was also investigated to determine the optimal preparation conditions. Cell parameters of R-doped YAG phases as a function of R3+ size were found to decrease, in general, as the atomic number of R increased due to lanthanide contraction, as indicated by x-ray diffraction data. The intensity of luminescent emission for R-doped YAG phase was found to first increase with increasing activator R concentration (i.e., x), then reach a maximum and finally decrease as x further increases. In order to investigate the concentration effect of Sm activator on the spectral properties and color characteristics, we have also prepared a series of (Y3-xSmx)Al5O12 phases with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, respectively. The cell parameters (a0) of Sm-doped YAG as a function of activator concentration x were discovered to increase with increasing x. This observation was attributed to the larger size of Sm3+ compared to that of Y3+. On the contrary, the intensity of emission spectra of Sm-doped YAG was found to decrease with increasing x. To understand the boundaries of color mixing and compare colors with different intensity values, we have also established CIE chromaticity diagrams for two series of (Y2.95R0.05)Al5O12 and (Y3-xSmx)Al5O12 phosphors, based on the data extracted from photoluminescent emission and excitation spectra.

碩士
崑山科技大學
機械工程研究所
101
The main purpose of this thesis is to develope a new phosphate fluorescent material and to study its characteristics. potassium phosphate zinc (KZnPO4) with hexagonal structure doped with the rare earth ion Eu3+, Tb3+, Sm3+ and Dy3+ as activator was studied in this thesis. Additionally, we investigated the effects of the doping concentration and sintering temperature on the microstructural and optical properties of potassium phosphate zinc (KZnPO4) By X-ray diffraction (XRD), photoluminescence spectrum (PL), and scanning electron microscop (SEM). The results showed that the best doping concentration of the activator Eu3+ is 0.04, the best sintering temperature is 1200 ℃,and the best Package proportion is 1:8. When the Tb3+ activator was doped, the optimum doping concentration is 0.12, the best sintering temperature is 1200 ℃，and the best Package proportion is 1:8. When the Sm3+ activator was doped, the optimum doping concentration is 0.007, the best sintering temperature is 1100 ℃，and the best Package proportion is 1:8. When the Dy3+ activator was doped, the optimum doping concentration is 0.002,the best sintering temperature is 1000 ℃,and the best Package proportion is 1:8.