Ca 1xy Dy x K y WO 4 : A novel near UV converting phosphor for white light emitting diode A.K. Ambast, J. Goutam, S. Som, S.K. Sharma ⇑ Department of Applied Physics, Indian School of Mines, Dhanbad 826004, India highlights  This paper reports structural and luminescence properties of calcium tungstate phosphors.  Color tunability and white light emission was achieved from these phosphors.  These indicate possible applications of these phosphors in phosphor converted w-LEDs. graphical abstract article info Article history: Received 12 June 2013 Received in revised form 14 October 2013 Accepted 2 November 2013 Available online 16 November 2013 Keywords: Phosphor Tungstate White LED abstract A series of Dy 3+ /K + doped calcium tungstate phosphors were synthesized by solid state reaction method. The crystal structure, surface morphology, chemical composition and photoluminescence properties of the prepared phosphors were investigated. The luminescence decay curves of doped/codoped phosphors were recorded. The X-ray diffraction analysis shows that the phosphors are of tetragonal structure. SEM studies confirm the particle size in the micro-meter (lm) range. The photoluminescence results indicate that these phosphors could be efficiently excited by the near-ultraviolet radiation which causes the emis- sion in the blue and yellow regions. The white light was achieved by tailoring this yellow to blue ratio varying the Dy 3+ /K + dopant concentration. The quality of emitted white light was checked by calculating different CIE parameters of these phosphors. Decay kinetics studies confirms the life time of activator ions in micro-second (ls) range. Ó 2013 Elsevier B.V. All rights reserved. Introduction Recently, the study of optical spectra of scheelite type (AXO 4 , A = Ca, Sr and Ba; X = Mo, W and V) materials attract intensive research attention owing to their good thermal and chemical prop- erties. High melting point (1450 °C), high refractive index (1.98) and low vibrational frequency (850 cm 1 ) make these materials as the promising candidates in light emitting diodes (LEDs) [1,2]. Now a days, white light-emitting diodes (w-LEDs) have attracted increasing attention due to the advantages of long lifetime, high luminescence efficiency and environmental-friendliness [3]. w-LEDs based on phosphors have been produced by a combination of a blue LED coated with a yellow phosphor. Recently, another approach to generate white light has been suggested which utilizes Red/Green/Blue tri-color phosphors excited by near UV (n-UV) light [4]. n-UV phosphor converted LEDs are expected to have many potential applications due to their excellent optical stability, high color tolerance and high conversion efficiency. So, a careful selection of phosphors that are efficiently excited by near-UV light are highly desirable. The luminescence properties of Dy 3+ ions have attracted much research attention due to the existence of two intense bands in 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.11.032 ⇑ Corresponding author. Tel.: +91 3262235412; fax: +91 3262296563. E-mail address: sksharma.ism@gmail.com (S.K. Sharma). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 93–99 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa