Tuning The Luminescence Of Double Perovskite Oxide Phosphors For Solid State Lighting Applications

The ability to control photoluminescence tuning in white light-emitting diodes(white-LEDs)is a crucial characteristic influenced by the modification and optimization of the phosphors design.It remains a challenge for developing luminescent materials with broad and continuously tunable photoluminescence to produce high-quality warm white light with an optimal correlated color temperature(CCT),an excellent color rendering index(CRI),and superior thermal stability.Phosphors are used as a down-converting medium to convert high-energy radiation,UV,near-UV,or blue,into visible light,producing white light.Due to its exceptional characteristics,such as high efficiency and superior lifetime,the combination of the blue-emitting chip(InGaN)and yellow emitting(YAG:Ce3+)phosphor is currently a commercial source of white light.However,due to the lack of a red color component,this combination could not meet the demand for efficient warm white light in the everyday home and office lighting applications.A combination of blue,green,and red phosphors coated on a near-UV emitting chip is another way to generate efficient white light.This combination satisfies the desire for warm white light,i.e.,both efficient and effective.However,reabsorption,which occurs when the excitation and emission bands of various phosphors overlap,reduces the device’s efficiency and operating life.Furthermore,the employment of multiple phosphors adds to the device’s complexity and cost.As a result,single-phase phosphors with high quantum efficiency and broader wavelength(covering the entire visible light spectrum)may help solid-state lighting gain traction in the market.As a result,finding novel efficient single-phase phosphors and inventing appropriate synthesis methods have gotten much attention worldwide.Research on broadly tunable single-phase all-inorganic materials conducted in this project focuses on applying solid-state lighting(SSL).The development of single-phase white light-emitting materials with a broad range is highly demanded.Transition metal and rare-earth ions,such as Bi3+,Sb3+,Dy3+,and Eu3+,are efficient activators because of their characteristic narrowband line emission across the visible spectrum.However,in the UV and blue spectral region,these ions characteristic dd and f-f absorption is forbidden,limiting their usefulness in diverse domains.It is observed that the synthesized Ca2ATaO6(A=Y3+and Lu3+)double perovskite oxide phosphors emit a highly efficient intrinsic emission in the blue spectral region under UV(300-400 nm)light excitation.The characteristic intrinsic blue emission was successfully used to sensitize these trivalent ions(Bi3+,Sb3+,Dy3+,and Eu3+)in the UV and blue spectral regions which in turns low energy emission in the entire visible region(400 nm-700 nm).The origin of the intrinsic blue emission and how it transferred some of its energy to sensitizing the activators were detailed studied.The present research work is divided into the following sections.1.In the first chapter of the thesis,different methods of white light technologies,development prospects,and advantages of solid-state lighting compared with other technologies are systematically introduced.In the second chapter,synthesis and characterization of the materials were shown in details.More specifically,XRD diffractogram and scanning electron microscopy(SEM)analysis were used to confirm the structure and morphology;high temperature and room temperature measurements were carried out luminescence spectroscopy.An energy transfer analysis among different activators was also detailed investigated.2.Chapter 3 reports the synthesis of a new composition of tunable color emitting phosphors which was successfully synthesized with a double perovskite structure.The luminescence of un-doped,doped and co-doped phosphors with Bi3+/Eu3+ions illustrate a broadband excitation ranging from 200-400 nm with dominant peak at 315 nm.The un-doped Ca2YTaO6 phosphors show an intense intrinsic emission centered at 424 nm.With the help of doping of Bi3+and Eu3+,the intense blue emission(424 nm)could be effectively tuned to blue,cyan,red,and white light.3.Chapter 4 illustrates the high-temperature solid-state synthesis of the Dy3+/Eu3+co-doped Ca2LuTaO6 phosphors with a double perovskite structure.With 313 nm excitation(UV light),the Ca2LuTaO6 double perovskite phosphors produce an intrinsic emission with a dominant peak at 424 nm.Computational and experimental approaches were used to investigate the origin of this broad-band blue emission.We doped Dy3+ and Eu3+in the Ca2LuTaO6 phosphors as a single and co-dopant to check for UV and near-UV excitation.Structure and phase analysis were investigated using X-ray diffraction and scanning electron microscopy.The study shows that Dy3+and Eu3+activated Ca2LuTaO6 double perovskite phosphors can emit narrowband multicolor lines with excellent efficiency for various applications through various characterizations such as photoluminescence excitation and emission measurements.4.Chapter 5 demonstrates how we synthesized Ca2YTaO6:xSb3+double perovskites with broad-band spectral emission and doublet emission peaks in the blue and red spectral regions(418 nm and 687 nm,respectively).The photoluminescence excitation(PLE),emission(PL),fluorescence decay time,thermal stability,and CIE chromaticity coordinates have been measured to demonstrate the potential of Ca2YTaO6:Sb3+double perovskite oxide phosphors for a suitable emission of plant growth.Furthermore,we observed efficient energy transfer from the host emission to Sb3+ activators,which increased red emission.We employed computational techniques to examine the crystal structure,electronic bandgap,and electronic configuration.The morphology and phase identification was validated using SEM and powder X-ray diffraction.Phosphors with a far-red emission(687 nm)are a good choice for producing white LEDs for plant growth.5.Chapter 6 illustrates the structure properties relation of Eu2+ doped CaAl1xGaxSiN3 solid solution phosphors,which exhibit the influence of structure distortion on the luminescence features of the activated Eu2+ions having 5d4f spin allowed transition.6.Chapter 7 summarizes the current dissertation and discusses future research directions.