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<p>The entrapment of biomolecules within TEOS-based sol-gel derived organic/inorganic nanocomposite materials has proven to be a viable platform for the development of biosensors and solid-phase biocatalysts. In this thesis, a series of organically modified silica materials were prepared by a two-step aqueous processing method that was suitable for biomolecule entrapment, and were formed as submicron thick films by dipcasting. Dispersed additives, such as polymers (Class I materials) and covalently bound additives, such as organically modified silanes (Class II materials), were used to modify the internal environment compared to the undoped matrices and to correlate the properties of entrapped enzymes.</p> <p>The morphology of organically modified silica materials could be modified through the use of either separate or co-hydrolysis of the silane precursors, with the later method generating optically transparent materials. Fluorescence microscopy revealed chemical heterogeneity in materials that appeared to be homogeneous by brightfield or SEM.</p> <p>Fluorescence emission studies of a solvatochromic dye entrapped within the film confirmed that the internal chemical environment of the films was strongly affected by doping with polymers and organosilanes. The films showed a rapid initial change in chemical properties owing to solvent evaporation, followed by a much slower evolution over several months owing to continued condensation reactions within the film.</p> <p>A reagentless biosensor was designed based on co-entrapment of an enzyme and a fluorescently labeled polymer. The enzymes urease and lipase were selected for this study as both catalyze reactions that alter the local pH. By co-entrapping pH sensitive fluorophores (SNARF-I and fluorescein) bound to a high molecular weight polymer, it was possible to detect the analytes urea and glyceryl tributyrate using changes in the fluorescence intensity (fluorescein) or emission ratio (SNARF-l). By tuning the polarity of the matrix it was possible to optimize the sensitivity of the sensing film for both the polar and non-polar analyte.</p> / Doctor of Philosophy (PhD)

Undoped and doped Pb(Zr_xTi_1-x)O₃, i. e. PZT, ferroelectric thin films were prepared by chemical solution deposition and spin-coating method. The precursors for making the undoped PZT films were derived from lead acetate, zirconium n-propoxide, and titanium iso-propoxide. In addition, lanthanum acetylacetonate, neodymium acetate, and niobium ethoxide were introduced into the precursor solution to accomplish doping of the corresponding elements. Both doped and undoped PZT films were coated onto Pt/Ti/SiO₂/Si, RuO_x and single-crystal sapphire substrates of various thickness and annealed at a range of temperatures and times. The effects of dopants were studied in terms of the Curie temperature, crystal distortion, transformation temperature, microstructure, optical properties, and electrical properties. In addition to the dopant effect, the effects of substrates were also investigated with regard to crystallization and preferred orientation. The Curie temperature of the doped and undoped PZT films was determined by in-situ hot-stage transmission electron microscope (TEM) and compared with those of bulk ceramics. Lattice distortion and phase transformation were determined by x-ray diffraction (XRD). Microstructure of the films was characterized by using optical microscopy, scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM). Optical properties were characterized by a UV-VIS-NIR scanning spectrophotometer and electrical properties and fatigue testing were measured on a standardized RT66A using a Virtual-Ground circuit. It was observed that the addition of Nd and La dopants tends to enhance perovskite phase formation and improve electrical properties of PZT films. Higher refractive indices in La and Nd-doped PZT films imply that packing densities of PZT films are improved by adding dopants. Furthermore, the lower leakage currents and improved fatigue properties in PZT films were also observed by the addition of Nb dopants. / Master of Science

Yes / The fabrication of precious metal (ruthenium, osmium, gold, and iridium) nanocrystals from single atoms has been studied in real-time. The dynamics of the first stage of the metal nanocrystallisation on a doped (B,S)-graphitic surface are identified, captured, and reported. / We thank the Leverhulme Trust (Early Career Fellowship No. ECF-2013-414 to NPEB), the ERC (Grant No. 247450 to PJS), EPSRC (EP/F034210/1 to PJS).

This dissertation presents an investigation of the properties, especially the electrical properties, of doped ZnO films grown by plasma-assisted molecular beam epitaxy (MBE) under different conditions. The interest in investigating ZnO films is motivated by the potential of ZnO to replace the currently dominant ITO in industries as n-type transparent electrodes and the difficulty in achieving reliable and reproducible p-type ZnO. On the one hand, n-type ZnO heavily doped with Al or Ga (AZO or GZO) is the most promising to replace ITO due to the low cost, abundant material resources, non-toxicity , high conductivity, and high transparency. On the other hand, ZnO doped with a large-size-mismatched element of Sb (SZO) or co-doped with N and Te exhibits the possibility of achieving p-type ZnO. In this dissertation, the effects of MBE growth parameters on the properties of GZO have been investigated in detail. The ratio of oxygen to metal (Zn+Ga) was found to be critical in affecting the structural, electrical, and optical properties of GZO layers as revealed by x-ray diffraction (XRD), transmission electron microscopy (TEM), Hall measurement, photoluminescence (PL), and transmittance measurements. Highly conductive (~2×10-4 Ω-cm) and transparent GZO films (> 90% in the visible spectral range) were achieved by MBE under metal-rich conditions (reactive oxygen to incorporated Zn ratio < 1). The highly conductive and transparent GZO layers grown under optimized conditions were applied as p-side transparent electrodes in InGaN-LEDs, which exhibited many advantages over the traditional thin semi-transparent Ni/Au electrodes. The surface morphologies of GaN templates were demonstrated to be important in affecting the structural and electrical properties of GZO layers. In those highly conductive and transparent GZO layers with high-quality crystalline structures, studies revealed ionized impurity scattering being the dominant mechanism limiting the mobility in the temperature range of 15-330 K, while polar optical phonon scattering being the mechanism responsible for the temperature-dependence for T>150 K. The majority Sb ions were found to reside on Zn sites instead of O sites for lower Sb concentrations (~0.1 at.%), which can lead to a high electron concentration of above 1019 cm-3 along with a high electron mobility of 110 cm2/V-s at room temperature. The reduction in electron concentration and mobility for higher Sb concentrations (~1 at.%) was caused by the deterioration of the crystalline quality. ZnO co-doped with N and Te was also studied and the advantages of the co-doping technique and problems in achieving p-type conductivity are discussed.

This PhD work took place in the framework of theoretical research aimed at implementation of quantum computing schemes and algorithms in solid state devices. The electron and nuclear spins of dopant atoms implanted in silicon crystals, that already lie at the core of commercial diodes and the photovoltaic industry, are able to store quantum information longer than anything else in the solid state. Controlled manipulations of silicon qubits depend on the ability to tune the nanoscopic donor electron state: we provide a complete theoretical picture that includes, within the insightful and analytic framework of effective mass theory, the effects of the non-trivial silicon conduction band and the different lattice distortions caused by the implantation of the donor species. Calibration of the multi-valley bulk theory to account for binding energies and electron-nuclear hyperfine couplings allows improved estimates of the exchange splittings between two neighbouring donors, that provide the simplest handle for tuning two-qubit operations. Further refinements to our approach lead to exceptional agreement with experimental measurements of Stark effects, where an external electric field is used to enable local single qubit manipulations within global driving fields: we set reliable thresholds on such gating speeds across all group V donors. Finally, we propose a scalable scheme for silicon quantum computing that relies on the coherent transfer of information from Si:Bi donors, that are established as excellent memory qubits, to surface quantum dots that are easier to manipulate, within a topological surface code which enables outstanding tolerance to errors. Analysis of the optimal working regimes and inclusion of the leading sources of decoherence allow us to set out a robust design of the basic building block of future realizations.

Nitrogen-doped (N-doped) porous carbons have drawn increasing attention due to their high activity for electrochemical catalysis, and high capacity for lithium-ion (Li-ion) batteries and supercapacitors. So far, the controlled synthesis of N-enriched ordered mesoporous carbons (N-OMCs) for Li-ion batteries is rarely reported due to the lack of a reliable nitrogen-doping protocol that maintains the ordered mesoporous structure. In order to realize this, in this work, ordered mesoporous carbons with controllable N contents were successfully prepared by using melamine, F127 and phenolic resin as the N-source, template and carbon-source respectively via a solvent-free ball-milling method. The as-prepared N-OMCs which showed a high N content up to 31.7 wt% were used as anodes for Li-ion batteries. Remarkably, the N-OMCs with an N content of 24.4 wt% exhibit the highest reversible capacity (506 mA h g−1) even after 300 cycles at 300 mA g−1 and a capacity retention of 103.3%. N-OMCs were also used as electrode materials in supercapacitors and a capacity of 150 F g−1 at 0.2 A g−1 with stable cycling up to 2500 times at 1 A g−1 was achieved. These attractive results encourage the design and synthesis of high heteroatom content ordered porous carbons for applications in the field of energy storage and conversion.

Recently, researchers on nanoparticles and nanostructures has received a great deal of attention not only in the area of synthesis and characterization but also in their potential application in various high-technological applications. Nanomaterials are widely used not only for environmental and biological applications but also for electronic and sensing applications. Among various classes of nanomaterials, the metal oxide nanostructures possess particular important because of their significant physical and chemical properties which allowed them to be used for the fabrication of highly efficient nanodevices. The metal oxide nanomaterials are widely used for catalysis, sensing, and electronic devices, and so on. Due to the high-efficient applications, researchers have developed several synthesis strategies to prepare metal oxide nanostructures with tailored geometry and utilize them for a variety of applications. However, it is still desirable to prepare metal oxide nanomaterials with environment-friendly precursors and processes with varied size and morphology for their effective utilization in specific applications. This thesis focuses on the synthesis, characterizations and specific applications of two undoped and doped metal oxide nanostructures, i.e. zinc oxide (ZnO) and iron oxide (α-Fe2O3). The thesis highlights the development of novel synthesis techniques/procedures which are rapid, consume less energy and time, and are less cumbersome, more economical, especially because of the low temperature process. The other aspect of the thesis is to use the as-synthesized nanomaterials for several important applications such as sensors, photovoltaic, and photocatalysis. The thesis is divided into several chapters. Chapter 1 starts with a brief introduction of the metal oxide nanostructures and their various synthetic methods. In addition to this, a short review on the targeted applications, i.e. sensing, photovoltaic and photocatalytic, of this thesis was also discussed in this chapter. Finally, the chapter describes the objective and importance of the thesis. Chapter 2 deals with the details of the synthesis and characterization techniques used in this thesis. Two specific techniques, i.e. hydrothermal and thermal evaporation, have been used for the synthesis of various undoped and doped nanomaterials explored in this thesis. The synthesized nanomaterials were examined by variety of techniques in terms of the morphological, structural, optical, compositional and electrical properties. Moreover the prepared nanomaterials together were used for various applications such as sensing, photovoltaic and photocatalytic applications. In a word, this chapter provides all the detailed procedures for the synthesis, characterizations and applications of targeted nanomaterials in this thesis. Chapter 3 describes the main results and discussion of the thesis. This chapter is divided into several sections and each section describes the synthesis, detailed characterizations and particular application of a single metal oxide nanomaterial. Section 1 describes the growth, characterization and ammonia chemical sensing applications of well-crystalline ZnO nanopencils grown via facile and simple hydrothermal process using commonly used laboratory chemicals. Importantly, the fabricated ammonia chemical sensor exhibited ultra-high sensitivity. Section 2 demonstrates the use of ZnO balls made of intermingled nanocrystalline nanosheets for photovoltaic device application. Successful growth, characterizations and phenyl hydrazine chemical sensing applications based on Ag-doped ZnO nanoflowers was demonstrated in section 3 of this chapter. Section 4 describes the Ce-doped ZnO nanorods for the detection of hazardous chemical; hydroquinone. Section 5 exemplifies the facile growth and detailed structural and optical characterizations of In-Doped ZnO hollow spheres composed of nanosheets networks and nanocones. Finally, section 6 illustrates the utilization of α-Fe2O3 hexagonal nanoparticles for environmental remediation and smart sensor applications. Moreover the synthesized α-Fe2O3 hexagonal nanoparticles were characterized in detail in terms of their morphological, structural, compositional and optical properties. Chapter 4 briefly highlights the overall conclusion and an outlook for further investigations suggested by the work undertaken here for this thesis. / Τα τελευταία χρόνια τα νανοσωματίδια και οι νανοδομές έχουν προσελκύσει μεγάλο ερευνητικό ενδιαφέρον λόγω των σημαντικών δυνατοτήτων που προσφέρουν για εφαρμογές υψηλής τεχνολογίας. Τα νανοϋλικά χρησιμοποιούντα ευρέως τόσο για περιβαλλοντικές και βιολογικές εφαρμογές όσο και για εφαρμογές στην ηλεκτρονική και τους αισθητήρες. Μεταξύ των διάφορων κατηγοριών νανοϋλικών, οι νανοδομές μεταλλικών οξειδίων παρουσιάζουν ιδιαίτερο ενδιαφέρον λόγω των φυσικών και χημικών ιδιοτήτων τους, που τους επιτρέπουν να χρησιμοποιούνται για την κατασκευή νανοσυσκευών υψηλής απόδοσης, με χαρακτηριστικά πεδία εφαρμογών την κατάλυση, την ηλεκτρονική και τους αισθητήρες. Για τους σκοπούς αυτούς, έχει αναπτυχθεί πληθώρα μεθόδων για την σύνθεση και προετοιμασία νανοδομών μεταλλικών οξειδίων με επιθυμητές γεωμετρίες, ώστε να είναι κατάλληλα για διαφορετικές εφαρμογές. Παρόλα αυτά, εξακολουθεί να υπάρχει έντονο ενδιαφέρον για την παραγωγή τέτοιων υλικών σε διάφορα μεγέθη και μορφολογίες, με περιβαλλοντικά φιλικές μεθόδους, με απώτερο σκοπό την χρησιμοποίησή τους σε συγκεκριμένες εφαρμογές. Η παρούσα διατριβή εστιάζει στην σύνθεση, τον χαρακτηρισμό και τις εφαρμογές των νανοδομών δύο συγκεκριμένων μεταλλικών οξειδίων (ZnO και α-Fe2O3) με ή χωρίς προσμείξεις. Η διατριβή δίνει έμφαση σε νέες τεχνικές σύνθεσης, οι οποίες είναι γρήγορες, καταναλώνουν λιγότερη ενέργεια και είναι πιο οικονομικές κυρίως λόγω χαμηλότερης θερμοκρασίας επεξεργασίας. Οι δομές των νανοϋλικών που προκύπτουν, χρησιμοποιούνται σε διάφορες σημαντικές εφαρμογές, όπως είναι οι αισθητήρες, τα φωτοβολταϊκά και η φωτοκατάλυση. Η διατριβή χωρίζεται σε 4 κεφάλαια. Στο κεφάλαιο 1 δίνεται μία σύντομη εισαγωγή στις νανοδομές των μεταλλικών οξειδίων και τις διάφορες μεθόδους σύνθεσης. Παρουσιάζονται συνοπτικά τα είδη των εφαρμογών τα οποία θα αποτελέσουν αντικείμενο μελέτης και τέλος περιγράφονται οι αντικειμενικοί στόχοι και η σημασία της διατριβής. Το κεφάλαιο 2 πραγματεύεται λεπτομερώς τις τεχνικές σύνθεσης και χαρακτηρισμού που υιοθετούνται στο μεγαλύτερο μέρος της μελέτης. Συγκεκριμένα, για την σύνθεση των νανοϋλικών (με ή χωρίς προσμίξεις) χρησιμοποιούνται οι τεχνικές της υδροθερμικής και της θερμικής εξάχνωσης. Τα παραγόμενα νανοϋλικά μελετήθηκαν ως προς την σύνθεσή τους, καθώς επίσης και τις μορφολογικές, δομικές, οπτικές και ηλεκτρικές ιδιότητες. Στην συνέχεια, χρησιμοποιούνται για τα διάφορα είδη εφαρμογών που αναφέρθηκαν παραπάνω. Με άλλα λόγια, στο κεφάλαιο αυτό περιέχονται όλες οι λεπτομέρειες των διαδικασιών παραγωγής και των εφαρμογών. Το κεφάλαιο 3 περιλαμβάνει την παρουσίαση και συζήτηση των αποτελεσμάτων. Αποτελείται από διάφορες παραγράφους η κάθε μία εκ των οποίων περιγράφει την σύνθεση, τον χαρακτηρισμό και τις εφαρμογές ενός εκ των υλικών. Στην Παράγραφο 1 περιγράφονται η ανάπτυξη, ο χαρακτηρισμός των κρυσταλλικών ZnO νανομολυβδιών μέσω μίας απλής και εύκολης υδροθερμικής διαδικασίας, χρησιμοποιώντας συνηθισμένα εργαστηριακά υλικά, καθώς επίσης και η εφαρμογή τους ως χημικοί αισθητήρες αμμωνίας. Αξίζει να σημειωθεί ότι οι αισθητήρες που κατασκευάστηκαν επέδειξαν υπέρ-υψηλή ευαισθησία. Η παράγραφος 2 επιδεικνύει την χρήση ZnO σφαιρών που είναι κατασκευασμένες απο αναμιγμένα νανοκρυσταλλικά νανοφύλλα για φωτοβολταϊκές εφαρμογές. Η επιτυχής ανάπτυξη και χαρακτηρισμός ZnO νανολουλουδιών εμπλουτισμένα με Άργυρο καθώς επίσης και η χρήση τους σε εφαρμογές αισθητήρων φαινυλο-υδραζίνης παρουσιάζονται στην παράγραφο 3. Στην παράγραφο 4 περιγράφεται η χρήση ZnO νανοράβδων εμπλουτισμένων με Δημήτριο για την ανίχνευση της επικίνδυνης χημικής ουσίας υδροκινόνης. Στην Παράγραφο 5 παρουσιάζεται η ανάπτυξη και ο λεπτομερής δομικός και οπτικός χαρακτηρισμός κοίλων σφαιρών ZnO εμπλουτισμένων με Ίνδιο που αποτελούνται απο δίκτυα νανοφύλλων και νανοκώνους. Τέλος στην παράγραφο 6 περιγράφεται η χρήση εξαγωνικών νανοσωματιδίων α-Fe2O3 για περιβαλλοντική αποκατάσταση και εφαρμογές ευφυών αισθητήρων. Οι δομές αυτές χαρακτηρίστηκαν λεπτομερώς ως προς τη σύνθεση τις μορφολογικές, τις δομικές και τις οπτικές ιδιότητες. Στο κεφάλαιο 4 παρουσιάζονται τα συμπεράσματα της παρούσας διατριβής καθώς επίσης και προστάσεις για την περεταίρω διερεύνηση των υπό μελέτη συστημάτων.

Electronic and optical properties of semiconducting nanocrystals, that can be engineered and manipulated by various ways like varying size, shape, composition, structure, has been a subject of intense research for more than last two decades. The size dependency of these properties in semiconductor nanocrystals is direct manifestation of the quantum confinement effect. Study of electronic and optical properties in smaller dimensions provides a platform to understand the evolution of fundamental bulk properties in the semiconductors, often leading to realization and exploration of entirely new and novel properties. Not only of fundamental interests, the semiconductor nanocrystals are also shown to have great technological implications in diverse areas. Besides size tunable properties, introduction of impurities, like transition metal ions, gives rise to new functionalities in the semicon-ductor nanocrystals. These materials, termed as doped semiconductor nanocrystals, have been the subject of great interest, mainly due to the their interesting optical properties. Among different transition metal doped semiconductor nanocrystals, manganese doped systems have drawn a lot on attention due to their certain advantages over other dopants. One of the major advantages of Mn doped semiconductor nanocrystals is that they do not suffer from the problem of self-absorption of emission, which quite often, is consid-ered detrimental in their undoped counterparts. The doped nanocrystals are known to produce a characteristic yellow-orange emission upon photoexcitation of the host that is relatively insensitive to the surface degradation of the host. This emission, originating from an atomic d-d transition of Mn2+ ions, has been a subject of extensive research in the recent past. In spite of the spin forbidden nature of the specific d-d transition, namely 6A1 −4 T1, these doped nanocrystals yield intense phosphorescence. However, one major drawback of utilizing this system for a wide range application has been the substantial inability of the community to tune the emission color of Mn-doped systems in spite of an intense effort over the years; the relative constancy of the emission color in these systems has been attributed to the essentially atomic nature of the optical transition involving localized Mn d levels. Interestingly, however, the Mn emission has a very broad spectral line-width in spite of its atomic-like origin. While the long (∼ 1 ms) emission life-time of the de-excitation process is well-studied and understood in terms of the spin and orbitally forbidden nature of the transition, there is little known concerning the process of energy transfer to the Mn from the host in the excitation step. In this thesis, we have studied the ultrafast dynamic processes involved in Mn emission and addressed the issues related to its tunability and spectral purity. Chapter 1 provides a brief introduction to the fundamental concepts relevant to the studies carried out in the subsequent chapters of this thesis. This chapter is started with a small preview of the nanomaterials in general, followed by a discussion on semiconducting nanomaterials, evolution of their electronic structure with dimensions and size as well as the effect of quantum confinement on their optical properties. As all the semiconducting nanomaterials studied in the thesis are synthesized via colloidal synthesis routes, a separate section is devoted on colloidal semiconducting nanomaterials, describing various ways of modifying or tuning their optical properties. This is followed by an introduction to the important class of materials “doped semiconductor nanocrystals”. With a general overview and brief history of these materials, we proceed to discuss about various aspects of manganese doped semiconductor nanocrystals in great details, highlighting the origin of the manganese emission and the associated carrier dynamics as well as different reported synthetic strategies to prepare these materials. The chapter is closed with the open questions related to manganese doped semiconductor nanocrystals and the scope of the present work. Chapter 2 describes different experimental and theoretical methods that have been employed to carry out different studies presented in the thesis. It includes common experimental techniques like UV-Vis absorption spectroscopy, steady-state and time-resolved photoluminescence spectroscopy used for optical measurements, X-ray diffraction, trans-mission electron microscopy and atomic absorption spectroscopy used for structural and elemental analysis. Experimental tools to perform special studies like transient absorption and single nanocrystal spectroscopy are also discussed. Finally, theoretical fitting method used to analyse various spectral data has been discussed briefly. Chapter 3 deals with the dynamic processes involved in the photoexcitation and emission in manganese doped semiconductor nanocrystals. For this study, Mn doped ZnCdS alloyed nanocrystal has been chosen as a model system. There are various radiative and nonrdiative recombination pathways of the photogenerated carriers and they often compete with each other. We have studied the dynamics of all possible pathways of carrier relaxation, viz. excitonic recombination, surface state emission and Mn d-d transition. The main highlight of this chapter is the determination of the time-scale to populate surface states and the Mn d-states after the photoexcitation of the host. Employing femtosecond pump-probe based transient absorption study we have shown that the Mn dopant states are populated within sub-picosecond of the host excitation, while it takes a few picoseconds to populate the surface states. Keeping in mind the typical life-time of the excitonic emission (∼ a few ns), the ultra-fast process of energy transfer from the host to the Mn ions explains why the presence of Mn dopant ions quenches the excitonic as well as the surface state emissions so efficiently. Chapter 4 presents a study of manganese emission in ZnS nanocrystals of different sizes. By varying the size of the ZnS host nanocrystal, we show that one can tune the Mn emission over a limited range. In particular, with a decrease in host size, the Mn emission has been observed to red-shift. We have attributed this shift in Mn emission to the change in the ratio of surface to bulk dopant ions with the variation of the host size, noting that the strength of the ligand field at the Mn site should depend on the position of the Mn ion relative to the surface due to a systematic lattice relaxation in such nanocrystals. The ligand field affects the emission wavelength directly by controlling the splitting of the t2 and e levels of Mn2+ ions. The surface dopant ions experience a strong ligand field due to distorted tetrahedral environment which leads to larger splitting of these t2 and e states. We further corroborated these results by performing doping concentration dependent emission and life-time studies. In Chapter 5 addresses two fundamental challenges related to manganese photolumines-cence, namely the lack of a substantial emission tunability and presence of a very broad spectral width (∼ 180-270 meV). The large spectral width is incompatible with atomic-like manganese 4T1 −6 A1 transition. On the other hand, if this emission is atomic in nature, it should be relatively unaffected by the nature of the host, though it can be manipulated to some extent as discussed in Chapter 3. The lack of Mn emission tunability and spectral purity together seriously limit the usefulness of Mn doped semiconductor nanocrystals. To understand why the Mn emission tunability range is very limited (typically 565-630 nm) and to understand the true nature of this emission, we carried out single nanocrystal imaging and spectroscopy on Mn doped ZnCdS alloyed nanocrystals. This study reveals that Mn emission, in fact, can vary over a much wider range (∼ 370 meV) and exhibits widths substantially lower (∼ 60-75 meV) than reported so far. We explained the occur-rence of Mn emission in this broad spectral range in terms of the possibility of a large number of symmetry inequivalent sites resulting from random substitution of Cd and Zn ions that leads to differing extent of ligand field contributions towards the splitting of Mn d-levels. The broad Mn emission observed in ensemble-averaged measurements is the result of contribution from Mn ions at different sites of varying ligand field strengths inside the NC. Chapter 6 presents a synthetic strategy to strain-engineer a nanocrystal host lattice for a controlled tuning of the ligand field effect of the doped Mn sites. It is realized synthesizing a strained quantum dot system with the structure ZnSe/CdSe/ZnSe. A larger lattice parameter of CdSe compared to that of ZnSe causes a strain field that is maximum near the interface, gradually decreasing towards the surface. We control the positioning of Mn dopant ions at different distances from the interface, thereby doping Mn at different predetermined strain fields. With the help of this strain engineering, we are able to tune Mn emission across the entire range of the visible spectrum. This strain induced tuning of Mn emission is accompanied by life-times that is dependent on the emission energy which has been explained in terms of perturbation effect on the Mn center due to the strain generated inside the quantum dot. The spectacular emission tuning has been explained by modelling the quantum dot system as an elastic continuum containing three distinct layers under hydrostatic pressure. From this modelling, we found that the strain is max-imum at the interface and decreases continuously as one goes away from the interface. We also show that the Mn emission maximum red shifts with increasing distance of the dopants from the maximum strained region. In summary, we have performed a study on the photophysical processes in manganese doped semiconductor nanocrystals. We have emphasized in understanding of different dynamic processes associated with the manganese emission and tried to understand the true nature of manganese emission in a nanocrystal. This study has brought out some new aspects of manganese emission and opened up possibilities to tune and control manganese emission by proper design of the host material.