Luminescence and advanced mass spectroscopic characterization of sodium zinc orthophosphate phosphor for low-cost light-emitting diodes Savvi Mishra, a G. Swati, a B. Rajesh, a Kriti Tyagi, a Bhasker Gahtori, a B. Sivaiah, a N. Vijayan, a M. K. Dalai, a A. Dhar, a S. Auluck, a M. Jayasimhadri b and D. Haranath a * ABSTRACT: A new rare-earth-free NaZnPO 4 :Mn 2+ (NZP:Mn) phosphor powder has been developed by our group and investigated meticulously for the first time using secondary ion mass spectroscopy and chemical imaging techniques. The studies confirmed the effective incorporation of Mn 2+ into the host lattice, resulting in an enhancement of photoluminescence intensity. Phase pu- rity has been verified and structure parameters have been determined successfully by Rietveld refinement studies. The NZP:Mn phosphor powder exhibits strong absorption bands in the ultraviolet and visible (300–470 nm) regions with a significant broad yellow-green (~543 nm) emission due to the characteristic spin forbidden d–d transition ( 4 T 1 → 6 A 1 ) of Mn 2+ ions, indicating weak crystal field strength at the zinc-replaced manganese site. The decay constants are a few milliseconds, which is a pre-requisite for applications in many display devices. The results obtained suggest that this new phosphor powder will find many interesting ap- plications in semiconductor physics, as cost-effective light-emitting diodes (LEDs), as solar cells and in photo-physics. Copyright © 2015 John Wiley & Sons, Ltd. Keywords: luminescence; orthophosphates; ToF SIMS Introduction White light-emitting diodes (WLEDs) are gaining wide popularity as promising substitutes for next generation lighting sources. They have attracted much attention due to their unique proper- ties such as low-power consumption, high luminescence efficiency and longer lifetimes, when compared with the traditional incandescent and fluorescent lamps (1–4). For phosphor-based WLEDs, rare-earth activated inorganic com- pounds have been reported extensively in the literature (5,6). Among the many host lattices recognized to date, such as alumi- nates, sulfides, borates and phosphates, the orthophosphates (ABPO 4 family) have captivated researchers’ interests the most because of reports stating that they give brighter luminescence using transition metal ions as activators (7,8). Apart from being chemically and thermally stable, these phosphate group-based ABPO 4 phosphors have low phonon energy (9,10). They also display excellent optical and ferroelectric properties (11,12). For the orthophosphates, it has been reported that its phases crystal- lize into three basic shapes depending upon cation sizes (13,14). Apart from the usual trend of using rare-earth (RE) ions as activa- tors, transition metal ions (such as Mn 2+ ) are also gaining popu- larity in the field of eco-friendly lighting and display devices (15–17). The emission wavelength of Mn 2+ depends on the crystal field environment provided by the host framework. It gives strong green emission in a weak crystal field, i.e. when it is tetrahedrally coordinated. It also exhibits an orange-to-deep red emission in a strong crystal field site, i.e. when it is placed on an octahedral site (18). It has been reported that zinc ortho- phosphate (zincophosphate) host matrices show bright and uniform luminescence due to co-ordination flexibility and strong Zn–O–Zn linkages (7). In this paper, we report the results from structure, luminescence and dopant distribution studies using mass spectroscopic and photoluminescence techniques on Mn 2+ -doped sodium zinc or- thophosphate phosphor. Time decay curves at different concen- trations of Mn 2+ have also been studied. This new phosphor could find many applications in the realm of efficient lighting technologies. * Correspondence to: D. Haranath, CSIR-National Physical Laboratory, Dr K.S. Krishnan Road, New Delhi 110 012, India. E-mail: haranath@nplindia.org a Academy of Scientific and Innovative Research (AcSIR), CSIR-National Physical Laboratory, Dr K.S. Krishnan Road, New Delhi 110 012, India b Department of Applied Physics, Delhi Technological University, New Delhi 110 042, India Abbreviations: AcSIR, Academy of Scientific and Innovative Research; CSIR, Council of Scientific and Industrial Research; DFT, Density functional theory; GGA, generalized gradient approximation; IBZ, Irreducible Brillouin Zone; IPCC, Intergovernmental Panel on Climate Change; LED, light-emitting diodes; OLED, organic light-emitting diodes; QY, quantum yield; RE, rare earth; SEM, scanning electron microscope; UGC, University Grants Commission; WLED, white light-emitting diodes; XRD, X-ray diffraction. Luminescence 2016; 31: 348–355 Copyright © 2015 John Wiley & Sons, Ltd. Research article Received: 22 April 2015, Accepted: 5 June 2015 Published online in Wiley Online Library: 21 July 2015 (wileyonlinelibrary.com) DOI 10.1002/bio.2966 348