Govind B. Nair

Highly enterprising calcium zirconium phosphate [CaZr4(PO4)6:Dy3+, Ce3+] phosphor for white light emission

A series of CaZr4(PO4)6:Dy3+, CaZr4(PO4)6:Ce3+ and CaZr4(PO4)6:Dy3+, Ce3+ phosphors were prepared by the solid state reaction process. The phase formation was confirmed by X-ray powder diffraction (XRD) measurements. Morphological studies were performed using scanning electron microscopy. Raman spectra were studied to identify the scattering bands associated with the normal vibrational modes of the PO43− tetrahedron. The photoluminescence properties of the phosphors were systematically investigated. With increasing Dy3+ concentration in CaZr4(PO4)6:Dy3+ phosphor, the luminescence intensity first increases, reaches the maximum, and then decreases. A similar trend is followed by CaZr4(PO4)6:Ce3+ phosphors, with increasing Ce3+ concentration. A successful attempt was made to initiate the energy transfer mechanism from Ce3+ to Dy3+ ions in the CaZr4(PO4)6 host lattice. The CIE chromaticity coordinates of CaZr4(PO4)6:Dy3+ phosphor exhibited emission near the white-light region and hence, it is a potential candidate for UV excited white-LEDs (WLEDs). CaZr4(PO4)6:Dy3+, Ce3+ phosphor has its CIE chromaticity coordinates in the white light region, near the standard illuminant D65. Thermoluminescence (TL) studies on CaZr4(PO4)6:Dy3+, Ce3+ phosphor, which was performed to test its stability against low dose of gamma-ray exposure, are also documented.

A perspective perception on the applications of light-emitting diodes

Light-emitting diodes (LEDs) continue to penetrate the global market; their pervasiveness clearly being felt in such diverse fields as technological, socio-economic and commercial interests. The multi-billion dollar LED market is shared by various segments, including office and household lighting, street lighting, the automobile industry, traffic signals, backlighting for hand-held devices, indoor and outdoor signs and indicators, medicine, communication systems, crop cultivation using artificial light and many more. The technological development of LEDs has undergone many phases in different parts of the world. From the early discovery of luminescence to the invention of highly efficient organic LEDs, researchers have worked with the prime purpose of improving the performance of luminaires. The need to infuse the market with more efficient and cheaper products has been prevalent from the start. LEDs are a result of this uncontrolled desire of researchers to develop superior products that would displace existing products in the market. To understand what led to the current prominence of LEDs, we give a brief historical overview of the field followed by a thorough discussion of the positive features of LEDs. This work includes the basic requirements, advantages and disadvantages of LEDs in a variety of applications. A brief description of the diverse applications of LED in fields such as lighting, indicators and displays, farming, medicine and communication is given. Considerable importance is placed on discussing the possible difficulties that must be overcome before using LEDs in commercial applications.

Assessment of electron-vibrational interaction (EVI) parameters of YAG:Ce(3+), TAG:Ce(3+) and LuAG:Ce(3+) garnet phosphors by spectrum fitting method.

The electron-vibrational interaction (EVI) in 4f↔5d optical transitions of Ce3+ ions in YAG, TAG and LuAG garnet phosphors have been analysed in this work. The main EVI parameters that have been estimated and reported here are Huang-Rhys factor, effective phonon energy, Stokes shift, red shift and Zero-phonon line position. The EVI parameters were estimated from the room temperature photoluminescence results that were recently reported. The spectrum fitting method was employed to determine the EVI parameters. An emission band was modelled with the aid of the calculated EVI parameters. The agreement between the modelled emission bands with the experimentally obtained ones validated the estimated values of EVI parameters.

Synthesis and characterization of novel Na15(SO4)5F4Cl:Ce3+ halosulfate phosphors

A series of Na15 (SO4 )5 F4 Cl phosphors doped with Ce3+ ions was prepared using the wet chemical method. X-Ray diffraction studies were used to determine their phase formation and purity. Fourier transform infrared spectroscopy effectively identified the chemical bonds present in the molecule. The photoluminescence properties of the as-prepared phosphors were investigated and the Ce3+ ions in these hosts were found to give broadband emission in the UV range. For the thermoluminescence study, phosphors were irradiated with a 5 Gy dose of γ-rays from a 60 Co source. Chens half-width method was employed to calculate the trapping parameters from the thermoluminescence glow curve. Copyright

White Light-Emitting Novel Nanophosphors for LED Applications

Abstract White light-emitting diodes (wLEDs) have touched new heights in the lighting industry with their exceptional energy efficiency, high luminous output, marathon working life, and eco-friendly applications. Three major strategies are generally implemented to fabricate wLEDs; these include blending tricolor phosphors excited by UV light-emitting diodes (UV-LEDs) or combing a yellow phosphor with blue light-emitting diode (LED) or combing a UV excited single-phase white-emitting phosphor with UV-LED. Each of these strategies has the virtues and shortcomings of their own. In this chapter, these strategies have been described briefly and the novel phosphors for wLEDs have been enlisted. The luminescence properties of nanophosphors based on different types of host have been reviewed here. The significance of nanophosphors for LED-based applications has also been highlighted.