1 General Introduction to Upconversion Luminescence Materials .. 1
1.1 Energy Transfer Mechanism of the Upconversion
Materials ............................................... 4
1.2 The Category of the Upconversion Materials .............. 6
1.2.1 Lanthanide-based Upconverters .................... 7
1.2.2 Transition Metal Upconverters ................... 13
1.2.3 Mixed Rare Earth/Transition Metal Upconverters .. 14
1.2.4 Organic Upconverters ............................ 14
1.2.5 Lanthanide-doped Upconversion Nanomaterials ..... 15
1.3 Summary ................................................ 17
References .................................................. 17
2 "Wet" Chemical Synthesis and Manipulation of Upconversion
Nanoparticles ............................................... 21
2.1 Introduction ........................................... 21
2.2 Mechanism for the Synthesis of Monodisperse
Nanocrystals ........................................... 22
2.2.1 Nucleation ...................................... 23
2.2.2 Synthetic Techniques for the Separation
of Nucleation and Growth ........................ 26
2.2.3 Growth .......................................... 27
2.3 Synthesis Routes for the Upconversion Nanoparticles .... 34
2.3.1 Thermolysis Strategy ............................ 34
2.3.2 Hydro(Solvo)Thermal Strategy .................... 39
2.3.3 Other Methods for the Synthesis of the
Lanthanide-Doped Luminescent Nanoparticles ...... 41
2.3.4 Ultrasmall Upconversion Nanoparticles with
Bright Upconversion Luminescence ................ 42
2.4 Synthesis Routes for the Fabrication of the Core
@Shell Structured Upconversion Nanoparticles ........... 44
2.4.1 One-Pot Heating-Up Method ....................... 44
2.4.2 Successive Layer-by-Layer Strategy for the
Fabrication of Multi-shell-Structured
Upconversion Nanoparticles ...................... 46
2.4.3 Ostwald Ripening Strategy for the Fabrication
of Core@Shell Upconversion Nanoparticles ........ 48
2.4.4 Cation Exchange Strategy for the Fabrication
of Core@Shell Upconversion Nanoparticles ........ 49
2.5 Characterizations ...................................... 49
2.5.1 Optical Characterization ........................ 49
2.5.2 Chemical and Structural Characterization ........ 55
2.6 Summary and Perspectives ............................... 61
References .................................................. 62
3 Upconversion Luminescence of Lanthanide Ion-Doped
Nanocrystals ................................................ 73
3.1 Introduction ........................................... 73
3.2 Upconversion Emission Color Tunability ................. 74
3.2.1 Multi-color Emission Using Different Host-
Dopant Combinations ............................. 74
3.2.2 Doping Concentration-Induced Multi-color
Emission ........................................ 77
3.2.3 Tuning Upconversion Emission Using FRET or
LRET ............................................ 79
3.2.4 Single-Band Upconversion Luminescence ........... 80
3.2.5 Other Ways to Tune Upconversion Emission ........ 81
3.3 Strategies for Enhancement of Upconversion Efficiency .. 83
3.3.1 Selection of Novel Host Matrix .................. 83
3.3.2 Plasmonic-Enhanced Upconversion Luminescence .... 88
3.3.3 Fabrication of Highly Efficient Lanthanide
Upconversion Nanoparticles by Homogeneous
Doping .......................................... 91
3.3.4 Tuning the Excitation Wavelength ................ 92
3.4 Core@Shell Structure-Based Luminescence Engineering
of the Upconversion Nanocrystals ....................... 93
3.4.1 Enhancing Upconversion Luminescence with Core
©Shell Structure ................................ 93
3.4.2 Tuning Upconversion Emission Using Core@Shell
Structures ...................................... 98
3.4.3 Tuning of the Excitation Wavelength ............. 98
3.5 Upconversion Nanocrystals Versus Quantum Dots and
Dyes .................................................. 101
3.6 Summary and Perspectives .............................. 107
References ................................................. 108
4 Upconversion Nanoparticle-Based Nanocomposites ............. 121
4.1 Introduction .......................................... 121
4.2 UCNP-mSiO2 ............................................ 122
4.2.1 Two-Step Sol-gel Method for the Fabrication
of UCNPs-mSiO2 Nanocomposites .................. 125
4.2.2 One-Step Sol-gel Method for the Fabrication
of UCNPs-mSiO2 Nanocomposites .................. 126
4.2.3 Yolk-Shell UCNPs-mSiO2 Nanocomposites .......... 127
4.3 UCNPs-MNPs ............................................ 130
4.3.1 SiO2-Assisted Synthesis of UCNPs-MNPs
Multi-functional Nanocomposites ................ 132
4.3.2 Cross-Linker-Assisted Synthesis of UCNPs-MNPs
Multi-functional Nanocomposites ................ 133
4.3.3 Seed-Mediated Growth Method for the Synthesis
of UCNPs-MNPs Multi-functional Nanocomposites .. 134
4.3.4 Applications of UCNPs-MNPs Nanocomposites ...... 135
4.4 UCNPs-Metals .......................................... 137
4.5 UCNPs-Semiconductors .................................. 141
4.6 Summary and Perspectives .............................. 146
References ................................................. 147
5 Surface Modification and Bioconjugation of Upconversion
Nanoparticles .............................................. 159
5.1 Introduction .......................................... 159
5.2 Ligand Engineering .................................... 162
5.2.1 Ligand Exchange ................................ 162
5.2.2 Oxidation of Oleic Acid ........................ 169
5.3 Ligand Attraction ..................................... 171
5.4 Layer-by-Layer Assembly ............................... 174
5.5 Surface Modifications Using Silane Reagents ........... 175
5.6 Surface Polymerization ................................ 177
5.7 Surface Control During Synthesis ...................... 178
5.8 Summary ............................................... 180
References ................................................. 180
6 Upconversion Nanoparticles for Biomedical Imaging .......... 187
6.1 Introduction .......................................... 187
6.2 In Vitro and In Vivo Toxicity Assessment .............. 190
6.2.1 Recent Progress on Toxicity Assessment
of UCNPs ....................................... 191
6.2.2 Evaluation Methods for the Long-Term Toxicity
of UCNPs in Small Animals ...................... 192
6.3 Biomedical Imaging Using UCNPs Under 980-nm
Excitation ............................................ 193
6.4 Biomedical Imaging Using UCNPs Excited at Different
Wavelength ............................................ 197
6.5 Ultrasmall UCNPs for Biomedical Imaging ............... 198
6.6 Optical Tomography .................................... 200
6.7 Multimodal Imaging Using UCNPs ........................ 202
6.7.1 Upconversion PL and Magnetic Resonance
Imaging (MRI) .................................. 202
6.7.2 Upconversion PL and X-Ray Computed
Tomography (CT) ................................ 207
6.7.3 Upconversion PL and Positron Emission
Tomography (PET) ............................... 209
6.7.4 Upconversion PL and Single-Photon Emission
Computed Tomography (SPECT) .................... 210
6.7.5 Upconversion PL and Multimodal Imaging
(MRI/PET/SPECT/CT) ............................. 212
6.8 Upconversion Imaging Techniques ....................... 212
6.8.1 Imaging System ................................. 212
6.8.2 Penetration Depth Measurement .................. 218
6.9 Conclusion and Future Opportunity for
Upconversion-Based Biomedical Imaging ................. 224
References ................................................. 226
7 The Applications of Upconversion Nanoparticles in
Bioassay ................................................... 233
7.1 Introduction .......................................... 233
7.2 Heterogeneous Assay ................................... 234
7.3 Homogeneous Assay ..................................... 238
7.4 UCNPs for Encoding and Multiplexed Detection .......... 241
7.4.1 Tuning UCNPs' Material Composition for
Encoding and Multiplexed Detection ............. 244
7.4.2 Tuning UCNPs' Optical Surface Layer for
Encoding and Multiplexed Detection ............. 247
7.4.3 Tuning UCNPs' Luminescence Lifetimes for
Encoding and Multiplexed Detection ............. 247
References ................................................. 248
8 Upconversion Nanoparticles for Biosensing .................. 255
8.1 Introduction .......................................... 255
8.2 The Construction of UCNPs-Based FRET or LRET
Nanosensors with Different Energy Acceptors ........... 258
8.2.1 Organic Dyes as Energy Acceptors ............... 258
8.2.2 Noble Metal Nanoparticles as Energy Acceptors .. 262
8.2.3 Carbon Nanomaterials as Energy Acceptors ....... 264
8.2.4 Mn02 Nanosheets as Energy Acceptors ............ 267
8.3 Biosensing of Different Species of Analytes ........... 268
8.3.1 Biosensing of Ions ............................. 269
8.3.2 Biosensing of Gas Molecules .................... 271
8.3.3 Biosensing of Biomolecules ..................... 272
8.4 Detection Based on Magnetic Separation ................ 274
8.5 Detection Based on Quenching Effect of Heavy Metal
Ions .................................................. 276
References ................................................. 278
9 Upconversion Nanoparticles for Light-Activated Therapy ..... 285
9.1 Introduction .......................................... 285
9.2 UCNPs for Photodynamic Therapy ........................ 286
9.2.1 History and Mechanism of Photodynamic Therapy .. 286
9.2.2 Photosensitizers ............................... 289
9.2.3 UCNP-Based Photodynamic Therapy ................ 291
9.3 UCNPs for Chemotherapy and Gene Therapy ............... 314
9.3.1 NIR Light-Triggered Photoisomerization ......... 315
9.3.2 NIR Light-Triggered Photolysis ................. 319
9.3.3 NIR Light-Triggered Photoreduction ............. 328
9.4 UCNPs for Photothermal Therapy ........................ 329
9.5 Conclusion and Perspectives ........................... 330
References ................................................. 331
10 Upconversion Nanoparticles for Thermal Sensing ............. 343
10.1 Introduction .......................................... 343
10.2 Rare Earth-Doped Upconversion Nanothermometry ......... 348
10.2.1 Intensity Upconversion Nanothermometry ......... 348
10.2.2 Band-Shaped Upconversion Nanothermometry-FIR
Theory ......................................... 351
10.2.3 Lifetime Upconversion Nanothermometry .......... 359
10.2.4 Bandwidth Nanothermometry and Spectral
Position Nanothermometry ....................... 359
10.3 UCNP-Based Nanocomposite Materials for Nanothermotry .. 362
10.4 Upconversion Nanoparticles Versus Quantum Dots
Versus Gold Nanoparticles Versus Green Fluorescent
Protein as Nanothermometry ............................ 366
10.4.1 Quantum Dots (QDs) ............................. 366
10.4.2 Gold Nanoparticles (GNPs) ...................... 368
10.4.3 Green Fluorescent Protein (GFP) ................ 368
10.4.4 Comparison Between UCNPs, GNPs, QDs, and
GFP-Based Nanothermometers ..................... 369
10.5 Summary and Outlook ................................... 370
References ................................................. 371
11 Upconversion Nanoparticles for Other Applications .......... 375
11.1 Introduction .......................................... 375
11.2 UCNPs for Photovoltaic Cells .......................... 376
11.2.1 Solar Cell Operation Principle and Their
Obstacles ...................................... 377
11.2.2 Recent Solutions to the Above Obstacles ........ 379
11.2.3 Recent Progress in Upconversion-Assisted
Solar Cell ..................................... 381
11.2.4 Conclusion and Future Opportunity
for Upconversion-Assisted Solar Cell ........... 383
11.3 UCNPs for Photocatalysis .............................. 386
11.3.1 Photocatalysis Mechanism ....................... 386
11.3.2 Obstacles and Recent Solutions for
Photocatalysis ................................. 388
11.3.3 Recent Progress in Upconversion-Assisted
Photocatalysis ................................. 390
11.3.4 Conclusion and Future Opportunity for
Upconversion-Assisted Photocatalysis ........... 394
11.4 UCNPs for Security Application ........................ 396
11.5 UCNPs for Optical Storage, Remote-Control
Photoswitching and Other Applications ................. 403
References ................................................. 404
12 Conclusions and Perspectives ............................... 409
Index ......................................................... 413
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