PHOTOLUMINESCENCE STUDIES OF CERTAIN RE IONS DOPED PHOSPHATE GLASSES FOR PHOTONIC APPLICATIONS

Abstract

Recent innovations based on solid-state lighting (SSL) have contributed significantly and practically to the lighting sectors. Small size, durable, and environmentally friendly, SSL devices consumed very little energy. When compared to other convectional light sources such as incandescent lamps, electric bulbs, and fluorescent tubes, The SSL based w-LEDs are more superior because they have a longer lifespan, use less energy, have great color rendering, small size, and environmental friendly nature. The advancement of superior white light-emitting diodes (w-LEDs) as lighting sources has become crucial for lowering global energy consumption in artificial lighting. Currently, the blue LED and YAG: Ce3+ phosphor serve as the foundation of the produced commercial w-LED. The w-LEDs that are now in use have various drawbacks, including a low color rendering index, an incorrect color temperature, and a halo effect. Phosphors can be replaced with RE activated glass to overcome the limitations. Glass also possesses a number of unique qualities, including a simple, efficient production method, strong chemical and thermal stability, as well as a high level of RE solubility. In light of this, various photonic devices, including w-LEDs, may benefit from effective RE activated glass. The RE-activated glasses are directly useful for a variety of applications, including solid-state lasers, optical fibre, sensors, light converters, and other innovative optoelectronic devices. The efficacy of the glass matrix host for all of these photonic device applications is investigated through spectroscopic analyses of characteristics including absorption, excitation, emission, and temperature-dependent photoluminescence (PL) characteristics recorded for the RE ions vii doped glasses. By selecting the right host glass composition or altering the RE ion concentration in a glass, one may change certain spectral properties. Based on special applications like solid state lasers, RE doped glasses exhibit distinctive optical characteristics in a variety of host glasses like phosphate, borate, silicate, telluride, and chalcogenides. A good former along with intermediates and network modifier can help in improving the lasing characteristics of glass hosts. Choosing a host glass with different RE ions for the optimal optical and lasing capabilities is still a challenging task. A dependable material for the construction of lighting devices is host glass with relatively low phonon energy, which increases the stimulated emission cross-section and quantum efficiency. There are several glass formers, including fluorides, phosphates, borates, tellurites, silicates, and borosilicate, that have been created and used to study different spectroscopic characteristics. Due to its unique characteristics, including clear visibility in a broad spectrum, softening, a lower melting point, good thermal stability, high RE solubility, and low dispersion, phosphate is one of the most ideal glass formers. Although phosphate glasses have several uses in photonic devices, their hygroscopic nature and weak chemical stability pose certain restrictions. The main focus of the current work is to investigate the benefits of heavy metal oxide glasses that are well suited for photonic devices such as lasers, fiber amplifiers, and light emitting diodes. We looked into these RE-ionized glasses because of the importance of heavy metal oxides in research and technology. In accordance to the aforementioned discussion, the combination of BaO, ZnO, Li2O, and P2O5 glasses can fulfil the requirement. constituent parts after assessing all the scientific patronages supplied by for the present inquiry. To improve the composition and concentration of RE ions for greater luminescence efficiency, we considered creating a suitable optical system, namely Barium Zinc Lithium Phosphate (BZLP) glasses. viii Several chapters make up this thesis' structure in order to meet all of the objectives of the research. Each chapter is structured such that it may be read alone. Chapter 1 begins with a clarified introduction, the cause of the issue, the inspiration behind the study, and a summary of recent literature. This chapter describes why 15 BaO-15ZnO-10Li2O 60P2O5 glasses are preferred for photonic devices like lasers and w-LEDs over a variety of other glasses. The characteristics of the various chemical components found in the host glass have been explored in length in this approach. Further research was done on the utility of RE ions when they are doped with glasses for usage in photonic devices. Several radiative metrics, including transition probabilities, branching ratios, radiative durations, stimulated emission cross-sections, and quantum efficiencies of the major excited levels, have been compiled using Judd-Ofelt (J-O) theory. The Inokuti-Hirayama (I-H) model, which is used to investigate the mechanisms of luminescence decay and energy transfer, has been explained. It has also been detailed how to use the luminescence spectra to calculate the CIE chromaticity color coordinates (x, y) to assess the white light tunability. Temperature dependent PL emission investigation signifies the utility of thermal stability of the prepared glasses in W-LEDs applications. Chapter 2 focuses on the experimental procedure utilized to prepare RE doped glasses as well as the procedures for analyzing the luminescence characteristics of the as prepared glasses. The melt quench method, which is used to synthesize the as-prepared glasses, is also thoroughly discussed. In order to study different properties, including thermal, structural, PL, and colorimetric properties, this chapter describes the use of numerous advanced experimental techniques, including differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV-VIS spectrophotometer, and spectrofluorophotometer. ix Chapter 3 develops trivalent dysprosium (Dy3+) activated BZLP glasses for the possible applicability of prepared glasses in photonic device applications, numerous structural, optical, and radiative characteristics have been explored in detail. The non-crystalline character of BZLP glass has been confirmed with the help of an XRD pattern. The titled glasses doped with Dy3+ ions show several absorption peaks in 330-2000 nm range with an indirect optical band gap of 3.41-3.76 eV. The J-O theory was employed on the absorption profiles and estimated various radiative parameters for the Dy3+ ions activated BZLP glasses. The Dy3+ ions activated glasses exhibit intense excitation at 350 nm and three sharp visible emissions at blue ( 4F9/2→6H15/2), yellow (4F9/2→6H13/2), and red ( 4F9/2→6H11/2). To ascertain the lasing potentialities of BZLP glasses, the stimulated emission cross-section and branching ratios have been assessed by correlating the emission spectral information with the radiative parameters calculated from the absorption spectral features. The colorimetric properties show the coordinates situated in a bright white region. Temperature-dependent photoluminescence (TD PL) spectral features recorded revealed the thermal stability of as-prepared glasses. The explored distinctive features for Dy3+ ions activated BZLP glasses suggested the superiority and direct utility of the as-prepared glasses in advanced photonic device applications such as lasers and w-LEDs. The content of this chapter has been published in an international journal Optical Materials 129 (2022) 112518] (IF: 3.754) Chapter 4 deals with Tb3+ doped BZLP glasses and investigated thoroughly using spectroscopic techniques such as XRD, UV-VIS absorption and PL to explore their utility in visible photonic device applications. The information pertaining glass transition temperature, melting temperature and thermal stability were understood by using recording the DSC spectrum for an un-doped BZLP glass. The total weight loss during the glass composition melting process was analyzed using thermo gravimetric curves. The UV spectral information recorded for the titled x glasses reveal the optical band gap falling in the range from 4.57 to 4.19 eV. The prepared Tb3+ doped BZLP glasses exhibit intense green emission along with relatively less intense blue, yellow and red peaks under 373 nm excitation. In the resultant PL spectra, the emission intensity increases with the activator concentration of Tb3+ ions from 0.5 to 5.0 mol%. The estimated CIE chromaticity coordinates falling in the green region reveals the aptness of the titled glasses as a green constituent in visible photonic devices. The PL decay curves show the bi-exponential behaviour with an average decay time of 2-3 ms. The temperature-dependent PL profile shows fewer changes in spectra and has a relatively high activation energy value, confirming the high thermal stability. Various results obtained for Tb3+ doped BZLP glasses finally reveal their usage as a green emitter needed to fabricate w-LEDs and other green emitting photonic device applications. The results of this chapter has already appeared in an International Journal Optical Materials 137 (2023) 113533] (IF: 3.754) Chapter 5 describes the structural, physical and spectral analysis Pr3+ doped BZLP glass samples synthesized through melt quenching route were studied. The x-ray diffraction (XRD) confirms the amorphous non-crystalline nature of an un-doped and doped BZLP glass. Absorption spectra show several bands in ultraviolet, visible and infrared regions. The absorption data was used in J-O theory to evaluate various radiative parameters. Three peaks are visible in the PL emission spectra with the strongest peak positioned at 604 nm for which stimulated emission cross section and quantum efficiency has been assessed. The CIE color coordinates of the samples lie in the red region. The decay time values for 604 nm emission decreased with increased Pr3+ concentration. The luminescence intensity decreased to 88.12% and 82.61% of maximum value at 423 K and 473 K respectively showing high thermal stability. xi These BZLP glasses can work as an effective deep red-emitting component for w-LEDs and other photonic applications. The content of this chapter has been published in Optical Materials 140 (2023) 113910 (IF: 3.754) Chapter 6 provides a summary of the general research effort given in this dissertation as well as the specific conclusions reached from the findings. This chapter also explores how the current work might be expanded and utilized upon going forward to guide new lines of investigation.