Cover
Title Page
Copyright
Preface
1 Introduction to Upconversion and Upconverting Nanoparticles
1. 1.1 Introduction
2. 1.2 Frequency Conversion and Its Various Processes
3. 1.3 Transition Metals and Their Properties
4. 1.4 Rare Earths and Their Properties
5. 1.5 Excitation and De‐excitation Processes of Rare Earths in Solid Materials
6. 1.6 Rate Equations Relevant to UC Mechanism
7. 1.7 Theoretical Description of Optical Characteristics of Rare‐Earth Ions
8. 1.8 An Introduction to Upconverting Nanoparticles
9. Acknowledgments
10. References
2 Synthesis Protocol of Upconversion Nanoparticles
1. 2.1 Introduction
2. 2.2 Host Matrix
3. 2.3 Synthetic Strategy of UC Nanomaterials
4. 2.4 Synthesis Techniques for Fabricating Core@shell Architectures
5. 2.5 Other Synthesis Strategies to Develop Lanthanide‐Doped UCNPs
6. 2.6 Conclusion
7. References
3 Characterization Techniques and Analysis
1. 3.1 Introduction
2. 3.2 X‐Ray Diffraction (XRD)
3. 3.3 X‐ray Photoelectron Spectroscopy (XPS)
4. 3.4 Field Emission Scanning Electron Microscopy (FESEM)
5. 3.5 Transmission Electron Microscopy (TEM)
6. 3.6 Energy‐Dispersive X‐ray Spectroscopy (EDS)
7. 3.7 Thermogravimetric Analysis (TGA)
8. 3.8 Ultraviolet–Visible–Near‐Infrared (UV–Vis–NIR) Absorption Spectroscopy
9. 3.9 Dynamic Light Scattering (DLS)
10. 3.10 Photoluminescence (PL) Study
11. 3.11 Pump Power‐Dependent UC
12. 3.12 Recognition of Emission Color and Colorimetric Theory
13. Acknowledgment
14. References
4 Raman and FTIR Spectroscopic Techniques and Their Applications
1. 4.1 Raman Spectroscopy
2. 4.2 Fourier Transform Infrared (FTIR) Spectroscopy
3. 4.3 Applications of Raman Spectroscopy
4. 4.4 Applications of FTIR Spectroscopy
5. 4.5 Raman and FTIR Spectroscopy of Upconverting Nanoparticles
6. References
5 Fundamental Aspects of Upconverting Nanoparticles (UCNPs) Based on Their Properties
1. 5.1 Introduction
2. 5.2 Elucidation of Dynamics of UCNPs on the Basis of Fluorescence Decay Times
3. 5.3 Measurement of Quantum Yield of UCNPs
4. References
6 Frequency Upconversion in UCNPs Containing Transition Metal Ions
1. 6.1 Introduction
2. 6.2 Synthesis of Transition Metal Ion‐Activated Luminescent Nanomaterials
3. 6.3 Structural and Optical Characterizations
4. 6.4 Frequency Upconversion and Its Various Mechanisms
5. 6.5 Applications
6. 6.6 Mechanism of Transition Metal Ions in Crystal Field
7. References
7 Frequency Upconversion in UCNPs Containing Rare‐Earth Ions
1. 7.1 Introduction
2. 7.2 Familiarization with the Spectroscopic Behavior of RE³ ⁺ Ion‐Doped UCNPs
3. 7.3 Routes to Enhance Upconversion Luminescence in Nanoparticles
4. 7.4 Technological Applications
5. References
8 Smart Upconverting Nanoparticles and New Types of Upconverting Nanoparticles
1. 8.1 Introduction
2. 8.2 Upconverting Core–Shell Nanostructures
3. 8.3 Hybrid Upconverting Nanoparticles
4. 8.4 Magnetic Upconverting Nanoparticles
5. 8.5 UC‐Based Metal–Organic Frameworks
6. 8.6 Smart UCNPs for Security Applications
7. 8.7 Smart Upconverting Nanoparticles for Biological Applications
8. 8.8 Smart Upconverting Nanoparticles for Sensing
9. 8.9 Conclusion
10. References
9 Surface Modification and (Bio)Functionalization of Upconverting Nanoparticles
1. 9.1 Introduction
2. 9.2 Upconverting Nanomaterials
3. 9.3 Surface Modification
4. 9.4 Biofunctionalization of Upconverting Materials and Applications
5. References
10 Frequency Upconversion in Core@shell Nanoparticles
1. 10.1 Introduction
2. 10.2 Synthesis of Core@shell and Core@shell@shell UCNPs
3. 10.3 Frequency Upconversion and Its Various Mechanisms
4. 10.4 Applications
5. 10.5 Conclusion
6. Acknowledgment
7. References
11 UCNPs in Solar, Forensic, Security Ink, and Anti‐counterfeiting Applications
1. 11.1 Introduction
2. 11.2 UCNPs for Solar Cells
3. 11.3 Forensic, Security Printing, and Anti‐counterfeiting Applications
4. 11.4 Biomedicals
5. 11.5 Display and Lighting Purposes
6. References
12 Application of Upconversion in Photocatalysis and Photodetectors
1. 12.1 Introduction
2. 12.2 Photocatalysis
3. 12.3 Photodetector
4. 12.4 Conclusion
5. References
13 UCNPs in Lighting and Displays
1. 13.1 Introduction
2. 13.2 Major Factors that Affect the UC Emission Efficiency
3. 13.3 UC Mechanisms with Rate Equations
4. 13.4 UCNPs in Solid‐State Laser
5. 13.5 UCNPs in Solid‐State Lighting and Displays
6. References
14 Upconversion Nanoparticles in pH Sensing Applications
1. 14.1 Introduction
2. 14.2 Basic Properties of UCNPs
3. 14.3 Working Principle of UCNP‐Based pH Sensor
4. 14.4 Photon Upconversion‐Based pH Sensing Systems
5. 14.5 Conclusion
6. References
7. Note
15 Upconversion Nanoparticles in Temperature Sensing and Optical Heating Applications
1. 15.1 Introduction
2. 15.2 Classification of Temperature Sensors: Primary and Secondary Thermometers
3. 15.3 Performance of Temperature Sensors
4. 15.4 Temperature Sensing with Luminescence
5. 15.5 Upconversion (UC) and UC‐Based Thermal Sensor of Ln³⁺ Ions
6. 15.6 Optical Heating
7. References
16 Upconverting Nanoparticles in Pollutant Degradation and Hydrogen Generation
1. 16.1 Introduction
2. 16.2 Degradation of Organic Pollutants
3. 16.3 Degradation of Inorganic Pollutants
4. 16.4 Photocatalytic Hydrogen Production
5. 16.5 Conclusion
6. References
17 Upconverting Nanoparticles in the Detection of Fungicides and Plant Viruses
1. 17.1 Introduction
2. 17.2 Visual Detection of Fungicides
3. 17.3 Detection of Plant Viruses
4. 17.4 Future Challenges Regarding NP‐Based Fungicide and Plant Virus Detection
5. References
18 Upconversion Nanoparticles in Biological Applications
1. 18.1 Introduction
2. 18.2 Upconversion Nanoparticles in Bioimaging
3. 18.3 Upconversion Nanoparticles in Drug Delivery
4. 18.4 Upconversion in Photodynamic Therapy
5. 18.5 Photothermal Therapy
6. References
Index
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List of Tables

Chapter 1
1. Table 1.1 Electronic configuration of trivalent ionic states of RE elements ...
Chapter 3
1. Table 3.1 List of upconversion nanomaterial's properties and name of the tec...
2. Table 3.2 List of upconversion nanoparticles (UCNPs) and their phase structu...
Chapter 5
1. Table 5.1 Summary of the constant parameters used in the simulations of stud...
Chapter 6
1. Table 6.1 Electronic configuration of transition elements (d‐block elements)...
Chapter 13
1. Table 13.1 Upconversion quantum yield in different upconverting nanoparticle...
Chapter 14
1. Table 14.1 Emission bands of various upconversion materials.
2. Table 14.2 Upconversion‐based pH sensors with their response time, range, an...
Chapter 15
1. Table 15.1 Comparison between the calculated value and measured value of tem...
2. Table 15.2 The temperature generated in different phosphor samples prepared ...
Chapter 16
1. Table 16.1 Degradation of RhB by typical UC photocatalysts.
2. Table 16.2 Degradation of MB by typical UC photocatalysts.
3. Table 16.3 Degradation of MO by typical UC photocatalysts.
4. Table 16.4 Degradation of various organic pollutants by typical UC photocata...
5. Table 16.5 Degradation of other pollutants by typical UC photocatalysts.
6. Table 16.6 Degradation of inorganic pollutants by typical UC photocatalysts....
7. Table 16.7 Summarized application of UC photocatalytic materials in hydrogen...
Chapter 17
1. Table 17.1 Summary of some works performed for plant virus biosensing.

List of Illustrations

Chapter 1
1. Figure 1.1 Basic energy‐level diagrams depicting typical anti‐Stokes process...
2. Figure 1.2 Schematic representation of possible UC mechanisms: (a) GSA/ESA, ...
3. Figure 1.3 Tanabe–Sugano diagram for the d³ electron configuration in the oc...
4. Figure 1.4 Splitting of 4f energy levels under different perturbations (draw...
5. Figure 1.5 Energy levels of the trivalent RE ions. Reprinted with permission...
6. Figure 1.6 Schematic representation of a three‐level energy system. The upco...
7. Figure 1.7 General strategies to achieve the high efficiency of UCNPs. Sourc...
Chapter 2
1. Figure 2.1 Flow chart representation of solid‐state reaction method. Source:...
2. Figure 2.2 Flow chart representation of coprecipitation technique. Source: P...
3. Figure 2.3 Schematic representation of sol–gel technique.
4. Figure 2.4 Schematic of hydrothermal synthesis and EDTA functionalization of...
5. Figure 2.5 Schematic description of the three main steps in solution combust...
6. Figure 2.6 Flow chart of Stöber technique. Source: PhD thesis of Lakshmi Muk...
7. Figure 2.7 Schematic illustration of three emulsion evaporation‐based prepar...
Chapter 3
1. Figure 3.1 Representation of diffraction from atomic plane: (a) Bragg's law ...
2. Figure 3.2 XRD patterns for cubic α‐NaYF₄ phase (JCPDS no. 77‐2042), mixed α...
3. Figure 3.3 Schematic representation of ejection of an electron from an atom ...
4. Figure 3.4 Instrumentation diagram of X‐ray photoelectron spectroscopy. Sour...
5. Figure 3.5 XPS spectra of NaYF₄@SnO₂ CSNPs (red line) and NaYF₄@SnO₂@Ag NPs ...
6. Figure 3.6 Schematic of the interactions of an electron beam with a sample a...
7. Figure 3.7 SEM images of the NaYF₄:Yb³⁺/Er³⁺ UCNPs synthesized using...
8. Figure 3.8 Comparative illustration of different components of a simple micr...
9. Figure 3.9 (a) TEM image of the SrSnO₃:1 at.% Ho³⁺ and 3 at.% Yb³⁺; ...
10. Figure 3.10 Instrumentation of energy‐dispersive X‐ray spectroscopy. Source:...
11. Figure 3.11 Energy‐dispersive spectra (EDS) of the NaYF₄:Yb,Tm UCNPs. Source...
12. Figure 3.12 Schematic diagram of a thermobalance and a control unit. Source:...
13. Figure 3.13 TGA of the NaYF₄:Yb³⁺/Er³⁺ UCNPs after coating with poly...
14. Figure 3.14 Schematic diagram of a UV–visible spectrophotometer. Source: Fah...
15. Figure 3.15 UV–vis spectra of UCNPs SrYbF:1% Tm dispersed in chloroform with...
16. Figure 3.16 Basic setup of a DLS measurement system. The sample is contained...
17. Figure 3.17 DLS size distribution plot of oleic acid capped hydrophobic NaYF
18. Figure 3.18 Schematic representation of a fluorescence spectrophotometer. So...
19. Figure 3.19 Upconversion luminescence spectrum of the NaYF₄:Yb/Er UCNPs exci...
20. Figure 3.20 Experimental setup used to observe the UC emission by using the ...
21. Figure 3.21 Pump power‐dependent upconversion luminescence spectra of the Na...
22. Figure 3.22 Instrumentation of colorimetry. Source: Ly et al. (2020). Reprin...
Chapter 4
1. Figure 4.1 A schematic presentation of Stokes Raman, anti‐Stokes Raman, and ...
2. Figure 4.2 Information obtained by the analysis of Raman peak.
3. Figure 4.3 Schematic presentation of relaxation processes in molecules.
4. Figure 4.4 Raman spectra of pure CH₃C≡N and (CH₃C≡N + CH₃OH) at different mo...
5. Figure 4.5 A schematic energy level diagram of upconversion nanoparticles. S...
Chapter 5
1. Figure 5.1 (a) Hypothetical decay of fluorescence from an electronically exc...
2. Figure 5.2 The four main energy transfer processes that are important for up...
3. Figure 5.3 Schematic representation of the GSA/ESA (a) and GSA/ETU (c) proce...
4. Figure 5.4 (a) Energy transfer upconversion (ETU) mechanism for two‐photon u...
5. Figure 5.5 (a) Schematic diagram of Yb/Tm upconversion emission pathways. In...
6. Figure 5.6 (a–c) Temporal evolution of upconversion emission at ∼480 nm with...
7. Figure 5.7 (a) Dependence of the frequency UC signal on the Nd³⁺ concent...
8. Figure 5.8 (a) Variation of the lifetime values of different emitting levels...
9. Figure 5.9 Comparative values of quantum yield (Ф) and quantum efficie...
10. Figure 5.10 Experimental setup of the absolute method of quantum yield measu...
Chapter 6
1. Figure 6.1 T–S diagram for (a) d³ electron. Source: Grinberg et al. (2017). ...
2. Figure 6.2 (a) The UC emission spectra of KZnF₃:1% Yb³⁺, x%Tm³⁺, 2.5...
3. Figure 6.3 Room temperature UC emission spectra of the optimized Ho³⁺, H...
4. Figure 6.4 (a) Upconversion luminescence (UCL) spectra of LiScSi₂O₆ (LSS):0....
5. Figure 6.5 (a) UC emission spectra of the NaGdF₄:Er³⁺/Yb³⁺/xFe³⁺
6. Figure 6.6 (a) Energy‐level diagram for Ni²⁺ in octahedral Cl₂ coordinat...
7. Figure 6.7 (a) Upconversion emission spectra of Y₂O₃:Ho³⁺–Yb³⁺ and Y
8. Figure 6.8 (a) Comparative UC emission spectra for different concentrations ...
9. Figure 6.9 (a) Comparative study of upconversion emission spectra of Bi_4xEr_x
10. Figure 6.10 Schematic energy‐level diagrams of OsX₆ ²⁻ (X = F, Cl, and ...
11. Figure 6.11 (a) Schematic illustration of synthesis procedures. (b) Photolum...
Chapter 7
1. Figure 7.1 (a) Comparative study of upconversion emission spectra of 1.0 mol...
2. Figure 7.2 Upconversion luminescence from the Ho³⁺‐, Yb³⁺‐co‐doped (...
3. Figure 7.3 (a) UC emission spectra of the Y₂WO₆:Tm³⁺ and Y₂WO₆:Tm³⁺–...
4. Figure 7.4 (a) The UC luminescence intensities of YPO₄:20% Yb³⁺/1% Tm³⁺...
5. Figure 7.5 Room temperature UC emission spectra of (a) NaYF₄:Yb/Er (18/2 mol...
6. Figure 7.6 UC fluorescence spectra of hexagonal‐phase (a) NaScF₄:Yb/Er and (...
7. Figure 7.7 Ratio of green to red emissions (RGR), and photographs of NaYF₄:2...
8. Figure 7.8 (a) Schematic drawing of FRET‐based multicolor silica/NaYF₄ NIR‐t...
9. Figure 7.9 Schematic illustrations of (a) energy transfer pathway from ICG o...
10. Figure 7.10 (a) Schematic design of a NaYF₄@NaYF₄:Tm@NaYF₄ core–shell–shell ...
11. Figure 7.11 (a) Color coordinate diagram of 0.4 mol% Ho³⁺–8.0 mol% Yb³⁺...
12. Figure 7.12 (a) Anticounterfeiting and information concealment schematic dia...
Chapter 8
1. Figure 8.1 Schematic scheme showing the synthesis method and bimodal lumines...
2. Figure 8.2 Demonstration of “direct” photoreactions of the DTE derivative tr...
3. Figure 8.3 Schematic diagram of the hybrid material showing down‐shifting an...
4. Figure 8.4 Scheme of the luminescence resonance energy transfer NaGdF₄Er³⁺...
5. Figure 8.5 Synthesis and characterization of the UC‐IO@Polymer nanohybrid. (...
6. Figure 8.6 In vivo cell tracking. (a) Fluorescence/upconversion images of mi...
7. Figure 8.7 (a) Schematic diagram depicting the structure of UCMOFs obtained ...
8. Figure 8.8 (a) Optical setup for excitation and imaging of patterns. (b) Por...
9. Figure 8.9 Scheme for producing anticounterfeiting hybrids. (a) Photograph o...
10. Figure 8.10 Scheme of multimodal imaging: a magnetic nanoparticle, a radionu...
11. Figure 8.11 (a) Crystal structure of cubic α‐NaYF₄ and hexagonal β‐NaYF₄. Mn
Chapter 9
1. Figure 9.1 Pictorial representation of sum frequency generation emission pro...
2. Figure 9.2 Upconversion emission intensities of upconversion nanoparticles (...
3. Figure 9.3 The schematic of possible biofunctional molecules and core@shell ...
4. Figure 9.4 Penetration of various optical wavelength penetration in the skin...
5. Figure 9.5 Live tracking images at (a) 0, (b) 3, and (c) 6 hours time interv...
6. Figure 9.6 In vivo imaging of rat: quantum dots (QDs) injected into the tran...
7. Figure 9.7 (a) Time‐resolved fluorescence‐Förster resonance energy transfer...
8. Figure 9.8 In vivo upconversion imaging after injection with NaYF₄:Yb:Tm@Fe_x
9. Figure 9.9 In vitro and in vivo images of HEK 293T cells after 5 minutes irr...
Chapter 10
1. Figure 10.1 Schematic diagram showing frequency downconversion and upconvers...
2. Figure 10.2 Absorption spectra (black lines) and photoluminescence (PL) spec...
3. Figure 10.3 (a) Bandgap tuning after core@shell formation. Middle: core QDs,...
4. Figure 10.4 Photoluminescence spectra of (a) YVO₄:5Eu³⁺ and (b) YVO₄:5Eu
5. Figure 10.5 Schematic diagram showing the core@shell formation: (a) the form...
6. Figure 10.6 (a) XRD patterns of core: NaYF₄ (i) and core@shell (NaYF₄@NaGdF₄
7. Figure 10.7 XPS spectra of core@shell (NaYF₄@NaGdF₄) at different excitation...
8. Figure 10.8 TEM images of (a) hexagonal β‐NaYF₄:Yb³⁺/Er³⁺ (15/2%) co...
9. Figure 10.9 TEM images of (a) hexagonal β‐NaYF₄:Yb³⁺/Er³⁺ (15/2%) co...
10. Figure 10.10 TEM images and particle size distribution of (a) hexagonal β‐Na...
11. Figure 10.11 (a) HAADF TEM images of NaYF₄ core@NaGdF₄ shell NCs at low magn...
12. Figure 10.12 (a, b) HAADF images of single NaYF₄ core@NaGdF₄ shell NCs and c...
13. Figure 10.13 ETU and EM processes in core and core@shell particles. The core...
14. Figure 10.14 UC emission spectra of core@shell nanoparticles: (a) NaErF₄:0.5...
15. Figure 10.15 UC emission spectra of (a) core@shell NaYF₄:Yb‐Tm@NaGdF₄ and (b...
16. Figure 10.16 (a) Looping mechanism or process in NaYF₄:1 at.% Tm³⁺ at 10...
17. Figure 10.17 The ground‐state electronic configurations of Yb³⁺ (a) and ...
18. Figure 10.18 (a) Energy level diagram showing sequential energy transfer fro...
19. Figure 10.19 Possible energy transfer mechanism in highly doped core: NaErF₄
20. Figure 10.20 (A) Possible core@shell nanostructures in which Er³⁺ and Yb
21. Figure 10.21 NIR III emission spectra of (a) NaErF₄:0.5 at.% Tm@NaYF₄ and (b...
22. Figure 10.22 Imaging of MCF 7 after interaction with 250 μg/ml of NPs shows ...
23. Figure 10.23 Internalization of NPs in HeLa cells. (a) Bright‐field image, (...
24. Figure 10.24 Four‐modal imaging of the focused tumor from the tumor‐bearing ...
25. Figure 10.25 FRET mechanism for heat generation. (a) Spectral overlap of UC ...
26. Figure 10.26 Schematic diagram of killing of cancer cells using FA‐coated na...
27. Figure 10.27 Schematic diagram showing Boltzmann distribution low for popula...
28. Figure 10.28 YPO4:Er‐Yb UCNPs: (a) Rise of FIR and temperature with the incr...
29. Figure 10.29 (a) Schematic diagram showing dual excitation at 800 or 980 nm ...
30. Figure 10.30 (a) Emission spectra of core@shell NaGdF₄:Yb‐Er@NaGdF₄:xNd UCNP...
31. Figure 10.31 Digital photos illustrating the application of core@shell UCNPs...
Chapter 11
1. Figure 11.1 (a) A schematic illustration of core–shell–shell nanoparticle's ...
2. Figure 11.2 (a) Upconversion emission spectra for Er³⁺/Ho³⁺‐codoped ...
3. Figure 11.3 A schematic of DSSCs attached with the upconverter layer. Source...
4. Figure 11.4 Number of upconversion material‐based paper publications per yea...
5. Figure 11.5 Schematic representation of steps of latent fingermark recording...
6. Figure 11.6 Identification of latent fingerprints using hexagonal NaYF₄:Ce³⁺...
7. Figure 11.7 Fingerprint demonstration on (a) paper surface and (b) transpare...
8. Figure 11.8 Schematic representation of (a) methods of formation of UCNPs co...
9. Figure 11.9 (a) Schematic diagram of constructing anti‐counterfeiting hybrid...
10. Figure 11.10 (a) Stamp of Chinese words used to write on plain paper; (b) hi...
11. Figure 11.11 A schematic illustration of the (a, b) working principle and de...
12. Figure 11.12 In vivo and in vitro imaging of rats: quantum dots and PEI‐coat...
13. Figure 11.13 SSOCT B‐scan images of chicken breast tissue; (a) control sampl...
14. Figure 11.14 Averaged A‐scan profile plot of the SSOCT image over the region...
15. Figure 11.15 (a) Synthesis of streptavidin‐functionalized NaYF₄:Yb³⁺,Er³...
16. Figure 11.16 (a) Upconversion luminesce spectra of composition of streptavid...
17. Figure 11.17 (a) Electroluminescence emission spectra of Yb³⁺/Er³⁺‐c...
Chapter 12
1. Figure 12.1 Energy‐level scheme showing the UC process in (a) Yb³⁺/Er³⁺...
2. Figure 12.2 UC emission spectra of (a) La₂O₃:Yb³⁺/Er³⁺, (b) La₂O₃:Yb
3. Figure 12.3 Mechanism of photocatalytic process based on a TiO₂ semiconducto...
4. Figure 12.4 (a) The proposed energy transfer mechanism of NaYF₄:Yb,Tm@TiO₂ u...
5. Figure 12.5 (a) Schematic illustration of the photocatalysis mechanism of β‐...
6. Figure 12.6 (a) FE‐SEM image of BiOBr:Yb³⁺/Er³⁺ nano/microcrystals f...
7. Figure 12.7 Photocatalytic mechanism of Au‐UCNPs/g‐C3N4 under (a) UV and (b)...
8. Figure 12.8 (a) TEM images of UCNPs‐CdSe nanostructure, (b) schematic repres...
9. Figure 12.9 (a) Schematic illustration, (b) SEM image of the MAPbI₃/UCNPs bi...
10. Figure 12.10 (a) Core–shell structure efficiently converted the incident SWI...
11. Figure 12.11 (a) Schematic diagram of the UCNPs/graphene hybrid micropyramid...
Chapter 13
1. Figure 13.1 The energy‐level scheme of a three‐level system and possible upc...
2. Figure 13.2 (a) Lasing spectra of the microcavity with a bottle‐like geometr...
3. Figure 13.3 (a) Numerical simulations of resonance spectrum and experimental...
4. Figure 13.4 Variation of UC emission intensity of green emission with temper...
5. Figure 13.5 Cathodoluminescence spectra of BaTiO₃:Er³⁺/Yb³⁺ and BaTi...
6. Figure 13.6 (a) The CIE chromaticity diagram associated with the emission co...
Chapter 14
1. Figure 14.1 (a) excited state absorption, (b) energy transfer upconversion, ...
2. Figure 14.2 Schematic diagram of an upconversion‐sensitized pH sensor. The p...
3. Figure 14.3 (a) Schematic description of the developed nanoprobe and its wor...
4. Figure 14.4 (a) Upconversion luminescence spectrum of dye‐conjugated UCNPs i...
5. Figure 14.5 Upconversion response of (a) NaYF₄:Er³⁺/Yb³⁺@NaYF₄@Ni an...
6. Figure 14.6 (a) The upconversion spectrum of Y₂O₂S:Er³⁺/Yb³⁺ UCNPs (...
7. Figure 14.7 (a) The upconversion spectra of the graphene oxide–PEI‐NaYF₄;Er³...
8. Figure 14.8 (a) Imaging calibration row (RGB) of the membrane. The graph at ...
Chapter 15
1. Figure 15.1 Schematic diagram of the effect of temperature on the emission s...
2. Figure 15.2 Emission spectra of NaYF₄:Yb³⁺/Er³⁺ UCNPs upon excitatio...
3. Figure 15.3 (a) UC luminescence spectra of OA‐capped C@S1@S2@S3 NPs in cyclo...
4. Figure 15.4 (a) UC luminescence spectra of Er³⁺ from ²H_11/2 and ⁴S_3/2 le...
5. Figure 15.5 A variation in the UC emission intensity of ²H_11/2 → ⁴I_15/2 (524...
6. Figure 15.6 Variation of blue UC emission (at 474 nm) intensity with time (i...
7. Figure 15.7 Variation of blue UC emission (at 475 nm) intensity with time (i...
8. Figure 15.8 Variation of blue UC emission (at 476 nm) intensity with time (i...
Chapter 16
1. Figure 16.1 The luminescence decays of the excited‐state levels of Er³⁺ ...
2. Figure 16.2 (a and b) SEM images of the UCNPs/CdS/PVP/TBT nanofibers develop...
3. Figure 16.3 Diagrams of the energy levels of Yb³⁺–Tm³⁺ and the upcon...
4. Figure 16.4 (a) Schematic illustrations for the preparation of the BVO/CF co...
5. Figure 16.5 (a) Schematic illustration of the NYF/AC composites synthesized ...
6. Figure 16.6 The proposed photocatalytic mechanism of the A/NYYE/WW photocata...
7. Figure 16.7 (a) Schematic illustration of the synthesis of UCNPs@Zn_xCd_1−x...
8. Figure 16.8 (a) The light absorption of each component in the MOF composites...
9. Figure 16.9 Possible mechanisms for photocatalytic hydrogen evolution of NYF...
10. Figure 16.10 Schematic of the interaction between the LSPR effect of W₁₈O₄₉ ...
Chapter 17
1. Figure 17.1 Different families of plant virus species. Source: Lefeuvre et a...
2. Figure 17.2 Jablonski diagram of FRET. Source: Hochreiter et al. (2015).
3. Figure 17.3 The distance between donor and acceptor can be changed by the am...
4. Figure 17.4 Structures as well as the absorption spectra of acceptors are ch...
5. Figure 17.5 Energy‐level diagram of the inner filter effect. Source: Zhang e...
6. Figure 17.6 Conditions for IFE‐based sensing, absorption spectrum of the abs...
7. Figure 17.7 Energy‐level diagram of (a) photoinduced electron transfer. Sour...
8. Figure 17.8 (a) Image of the fabricated sensing system. (b) Graph of quenchi...
9. Figure 17.9 (a) Schematic diagram of calorimetric detection of thiram via WL...
10. Figure 17.10 (a) Schematic representation of fluorescence‐based aptasensor f...
11. Figure 17.11 Scheme for IFE‐based Ag⁺ detection. Source: Long et al. (20...
12. Figure 17.12 IFE‐based detection of the Fe³⁺ ions. Source: Chen et al. (...
13. Figure 17.13 Interaction mechanisms between NPs and plant virus vector syste...
14. Figure 17.14 Schematic diagram of plant virus detection using antibody‐conju...
Chapter 18
1. Figure 18.1 (a) Whole‐body images of a BALB/c mouse injected via tail vein w...
2. Figure 18.2 (a) The UC PL, (b) bright‐field, and (c) merged images of a KB t...
3. Figure 18.3 Schematic representation of UCNP‐based drug delivery system: (A)...
4. Figure 18.4 Schematic representation of a polymer‐coated UCNP‐based drug del...
5. Figure 18.5 Schematic representation of ZnPC PS‐loaded mesoporous silica she...
6. Figure 18.6 Photothermal therapy and NIR‐controlled drug release of nanocomp...

Preface

The conversion of low‐energy photons into high‐energy photons, known as “frequency upconversion,” using advanced optical materials has become an emerging research field with wide consequence and impact in various scientific areas ranging from healthcare to energy and security. The materials showing frequency upconversion properties are known as upconversion (UC) materials. UC materials reveal variety of applications in different fields, viz. color display, two‐photon imaging in confocal microscopy, WLEDs, high‐density optical data storage, upconvertors, under sea communications, solid‐state lighting, sensors, photovoltaics, photocatalysis, food industry, indicators, anti‐counterfeiting, bioimaging, cancer therapy and other biological fields. It is known that in comparison to ultraviolet (UV) and visible light the near‐infrared (NIR) light is abundant and non‐destructive in nature. It has deep penetration in the organisms and less harmful quality. UC luminescent materials in nanosize range are known as UC nanomaterials or UC nanoparticles (UCNPs). UCNPs excited with non‐destructive NIR light are a better choice than the conventional downconversion nanoparticles because they are free from autofluorescence, have low light penetration, and cause less severe photo‐damage to living organisms. It is notable to mention that the low efficiency of UC materials definitely becomes a major barrier for their application in a wide range. For researchers, it is a top priority to overcome this problem. Several engineered UCNPs, e.g. organic, inorganic, hybrids, and thin films, have been explored widely to obtain highly efficient UC luminescent materials. Usually, organic luminescent materials suffer poor stability under harsh conditions and have poor long‐term reliability, but have a greater ductility than inorganic materials. The inorganic luminescent materials are more durable and possess high thermal stability. So, the hybrid materials consisting of both inorganic and organic components, namely, metal organic frameworks (MOFs), have attracted researchers with enhanced luminescence properties as compared to the bare organic and inorganic materials. To enhance the upconversion efficiency, spherical metal nanoparticles showing plasmon resonance in close proximity of the UCNPs are utilized. The plasmonic nanostructures are widely used to evolve the UCNPs with improved electronic, metallic, and optical properties. When the surface plasmon resonance wavelength of the metallic nanostructure matches with the excitation wavelength of upconversion mechanism, signal enhancement occurs. Usually, the coating of gold (Au) and silver (Ag) nanoparticles is used to tune the luminescence properties of UCNPs, though the nanoparticles exhibit plasmon absorption in 400–600 nm range.

The upconversion emission efficiency can be enhanced by several ways, including doping with sensitizer, non‐lanthanides, and coating with inorganic shell. The non‐lanthanide co‐doping in UCNPs has also been used frequently in order to get enhanced luminescence intensity along with the use of sensitizer ion. The co‐doping of activator and sensitizer ions with proper concentration in an appropriate host matrix is essential to achieve highly efficient UC emission as the concentration quenching has a prejudicial effect on the luminescence intensity. The phonon frequency, stability, cost effectiveness, non‐hygroscopic, and non‐toxic nature of the UC materials are of utmost importance. The security of any important data, currency, etc. has become very crucial to prevent counterfeiting. UCNPs with high luminescence intensity can be validated in anti‐counterfeiting applications. These materials are also utilized for visual exposure of fungicides, thiram, etc., which can be broadly applied in soybeans, apples, wine farming, etc., to avoid crop diseases and excessive use of pesticides. Rare‐earth‐ions‐based UC emission has tremendous advantages in terms of long excited lifetime, sharp emission bandwidth, low autofluorescence, high photostability, high resolution, low toxicity, etc. Rare‐earth ions are found to be very sensitive to even small changes in chemical surroundings. Therefore, it becomes essential to get information about the symmetry, bonding of the probe ion, and how they change their optical properties with chemical composition of the host materials. For getting the high quantum efficiency, concentration of the dopants should be high, but it may cause concentration quenching due to the interaction between the excited and unexcited neighbors. Therefore, the nano‐structured materials containing metallic nanoparticles are of particular interest because the large local field around the rare‐earth ions positioned near the nanoparticles may increase the luminescence efficiency. Among several strategies, the coating of upconversion nanoparticles with inorganic materials shell is an effective method to get enhanced UC luminescence. The core@shell approach offers shielding to the surface particles and thus reduces the surface defects and possibility of quenching. This core@shell architecture is very much beneficial in biomolecule conjugation and thus suitable for many biological applications. Different coating strategies have been employed according to the required application purposes. UCNPs probes can function as multiple contrast agents for concurrent use in altered medicinal imaging modalities by providing corresponding diagnostic information (i.e. MRI and CT). Bio‐conjugation on the surface of the UCNPs shows a much enhanced imaging performance in comparison to the clinically used fluorescent dyes. Innovative bio‐imaging methods are being established by combining the conventional medical imaging modalities using core‐shell structured UCNPs.

The book entitled Upconverting Nanoparticles: From Fundamentals to Applications is completely different from the previously published books in all respects, including the basics, scientific and technological demands. It is divided into eighteen chapters. Chapter 1, authored by Mondal and Rai, introduces the basic concepts of upconversion, and upconversion of nano‐particles. The introduction to frequency upconversion and its various mechanisms, excitation and de‐excitation processes in hosts containing rare‐earth ions along with the spectroscopic properties of rare‐earth ions/transition metals are described in this chapter. The rate equations relevant to excited‐state absorption and energy transfer processes with an overview of the UCNPs have been introduced. Chapter 2, authored by Mukhopadhyay and Rai, describes the synthesis protocol of upconversion nanoparticles. In this chapter introduction to host materials and synthesis strategies of UC nanomaterials like solid‐state reaction, co‐precipitation, sol–gel, hydrothermal, combustion, thermolysis, microwave‐assisted synthesis, core@shell synthesis techniques, etc. have been described. Chapters 3 and 4, authored by Jain et al.; Ojha and Ojha, refer to characterization techniques and analysis; Raman and FTIR spectroscopic techniques and their applications, respectively. Various structural and optical techniques for the characterization of UCNPs, viz. X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDS), thermogravimetric analysis (TGA), ultraviolet–visible–near infrared (UV–Vis–NIR) absorption spectroscopy, dynamic light scattering (DLS), photoluminescence, Fourier transform infrared (FTIR), have been reported. Chapters 5, 6 and 7, authored by Ranjan et al.; Prasad and Rai; and Pattnaik and Rai, summarize the fundamental aspects of UCNPs based on their properties, frequency upconversion in UCNPs containing transition metal ions, and frequency upconversion in UCNPs containing rare‐earth ions, respectively . Along with introduction the dynamics of UCNPs on the basis of fluorescence decay times, quantum yield measurement of UCNPs, frequency upconversion and its various mechanisms have also been interpreted. The various routes to enhance the upconversion luminescence along with the technological applications of UCNPs have been described.

Chapters 8, 9, and 10, authored by Singh; Dwivedi; and Ningthoujam et al., are devoted to the smart and new type of upconverting nanoparticles; surface modification and (bio) functionalization of upconverting nanoparticles, and frequency upconversion in core@shell nanoparticles, respectively. These chapters outline the upconverting core@shell nanostructures, hybrid upconverting nanoparticles, magnetic‐upconverting nanoparticles, UC‐based metal–organic frameworks, surface modification, bio‐functionalization of upconverting materials, synthesis of core@shell and core@shell@shell UCNPs, and use of UCNPs for security, biological, and sensing applications. Chapters 11, 12, 13, 14, and 15, authored by Kumar, Mishra and Shwetabh; Singh et al.; Dey; Mahata, De and Lee; and Shahi and Rai, deal with the UCNPs in solar, forensic, security ink, and anti‐counterfeiting applications; application of upconversion in photocatalysis and photodetectors; UCNPs in lighting and displays; upconversion nanoparticles in pH‐sensing applications and upconversion nanoparticles in temperature‐sensing and optical heating applications, respectively. Chapters 16, authored by Wang et al., throws the light on UCNPs applications in degradation of organic and inorganic pollutants along with the photocatalytic hydrogen generation. The visual detection of fungicides and plant viruses along with the future challenges have been explained by Kesarwani and Rai in Chapter 17. Chapter 18, authored by Mukherjee and Sahu, involves the application of UCNPs in bio‐imaging, drug delivery, photodynamic therapy, and photothermal therapy.

The present book is outcome of the untiring efforts of all the contributing authors. It will be very much helpful to the researchers as well as the undergraduate and post‐graduate students studying physics, chemistry, materials science, biology, engineering, etc. in gaining a proper understanding about the upconversion luminescence. It was possible to complete this book only due to the great affection and blessings of Gurudev Pt. Shri Ram Sharma Acharya and Gurumataji Mata Bhagawati Devi Sharma. Special thanks to all my family members and research scholars for their motivation and kind support. I would also like to thank the Wiley team involved from the beginning till the completion of the book proposal. As a large number of topics related to the UCNPs and their applications have been covered in this book, there could be the possibility that some of the minute glitches have been missed out. Therefore, genuine suggestions and comments from the readers are welcome. Overall, the research developments on UCNPs and their uses in different fields starting from very basics to advanced level make the present book unique.

Professor (Dr.) Vineet K. Rai
Department of Physics
Indian Institute of Technology (Indian School of Mines), Dhanbad, India