Synthesis and Optical Characterisation of Barium Magnesium Aluminate Nanophosphors as Blue Light Emitting Source

Abstract

Extensive research has been carried out on the blue light emitting phosphors till date. The blue phosphor is an important and promising candidate in display and lighting technology. BaMgAl10O17:Eu2+ (BAM:Eu2+) is the commercially used blue phosphor. The present work studies the photoluminescence properties of BAM:Eu2+ nanophosphors prepared by solution combustion synthesis process. Activator concentration, phase purity, crystallinity and morphology are the governing factors for high luminescence efficiency for any phosphor. Based on these factors various techniques were used and studied to enhance the photoluminescence efficiency of the BAM:Eu2+ nanophosphors. The entire work in this thesis is presented in seven chapters. The outline of these seven chapters is given below. Chapter 1 discusses the fundamentals of photoluminescence giving an insight into the trivalent and divalent rare earth ions as luminescent centers. This chapter also covers some important topics explaining luminescence phenomenon in phosphors. Red, green and blue light emitting phosphors are discussed concisely. Applications of phosphors are given in brief. Importance of blue phosphors and a brief introduction to BaMgAl10O17 host material concludes the chapter. Chapter 2 summarizes current research in the field of phosohors. Earlier reported work of various researchers has been reviewed. Effect of various parameters on morphological and optical properties of BAM has been given. The chapter discusses BAM phosphors along with different synthesis routes, effect of co-doping, alkali ion incorporation, polymer addition, theoretical assessment and degradation mechanism. The last section of the chapter gives gaps in the study and the objectives for the work presented in the thesis. Chapter 3 gives the experimental details followed for the synthesis of the materials and different characterization techniques used during the course of present study. The complete procedure of the synthesis technique along with different molar concentrations of different dopants, co-dopants and surfactants are given. Details of different techniques and instruments employed to characterize the prepared samples has been given in terms of their instrument names, model number and operating conditions. Sample names with their corresponding codes have been listed systematically in tabular form. Chapter 4 studies the photoluminescence properties of BAM:Eu2+ phosphor and the effect of pure phase on the photoluminescence properties of BAM:Eu2+ nanophosphor. The BAM:Eu2+ nanophosphor was prepared by solution combustion synthesis method. The modification in the synthesis route in terms of two additional steps namely acid leaching and annealing and their affect on the morphological and optical properties of BAM:Eu2+ nanophosphor has been discussed. To check the efficiency of the prepared nanophosphors, their CIE color coordinates and color purity has been calculated. Chapter 5 presents the effect of morphology on the photoluminescence efficiency of BAM:Eu2+ nanophosphor. β-cyclodextrin (β-CD) and thioglycerol (TG) were used as tempalate agents during synthesis of BAM:Eu2+ nanophosphors by solution combustion synthesis route. The enhancement in photoluminescence emission intensity of BAM:Eu2+ nanophosphor due to change in morphology through β-CD and TG inclusion has been discussed in detail. The CIE color coordinates and thermal stability results of the prepared nanophosphors has been studied to check their efficiency and applicability. Chapter 6 gives the detailed study on the effect of substitution or co-doping of Dy3+, Ca2+ and alkali metal ions Li+, Na+ and K+ on the structural and optical properties of BAM:Eu2+ nanophosphor prepared by solution combustion synthesis method. The chapter has been divided into three sections. The first section studies the effect of Dy3+ ions co-doping on structural and optical properties of BAM:Eu2+ nanophosphor. Thermoluminescence study of BAM:Eu2+ /Dy3+ nanophosphor has been analysed to obtain information about the traps created. The photoluminescence properties of BAM:Eu2+ /Dy3+ nanophosphor has been studied in detail. The second section of this chapter deals with the effect of alkali metal ion on the optical properties of BAM:Eu2+ nanophosphor. The third section studies the effect of Ca2+ co-doping on photoluminescence efficiency of BAM:Eu2+ nanophosphor. A detailed discussion has been given on the increase in the photoluminescence emission intensity of BAM:Eu2+ nanophosphor due to co-doping of these ions. The CIE color coordinates and color purity of all the samples have been calculated. Also, to check the usability and the efficacy of the prepared phosphors thermal stability of all the prepared phosphors has been studied. Chapter 7 summarizes and concludes the results obtained from the structural, morphological and optical characterisations of the samples prepared through different experiments and variations as discussed in the previous chapters. Finally, at the end of the chapter some suggestions for the future study in this field are given.