Effect of Zr 4+ and Si 4+ substitution on the luminescence properties of CaMoO 4 :Eu 3+ red phosphors T. Linda Francis • P. Prabhakar Rao • Mariyam Thomas • S. K. Mahesh • V. R. Reshmi Received: 11 February 2014 / Accepted: 20 March 2014 Ó Springer Science+Business Media New York 2014 Abstract A series of intense red emitting phosphors, Ca 0.8-x Zr x Mo 1-x Si x O 4 :0.2Eu 3? (x = 0.025, 0.05, 0.075, 0.1) that could be effectively excited in the UV region was prepared by conventional high temperature solid state reac- tion route. Structural, morphological and photolumines- cence properties of the prepared samples were studied in detail. The incorporation of Zr 4? and Si 4? ions in CaMoO 4 lattice maintained the powellite crystal structure. Lumines- cence properties were optimized for 7.5 mol% of Zr 4? and Si 4? concentration. Emission intensities improved more than twice in comparison with CaMoO 4 :Eu 3? . Life times of the prepared samples improved and the quantum efficiency enhanced to *39 %. The improvement in emission intensity and quantum efficiency is explained in terms of the local distortion around the Eu 3? ions resulting in improved absorption in the UV region. The CIE color co-ordinates of the red emission were in agreement with the values of the standard red phosphors providing potentiality to be used in phosphor converted (pc) white LEDs. 1 Introduction A novel red phosphor material that can be effectively excited in the near UV and visible region with good absorption and emission properties, good thermal and chemical stability and high quantum yield is of great demand in the solid state lighting applications particularly in the development of pc-white LEDs [1, 2]. Molybdates with powellite structure are reported as good host lattices under near UV/blue excitation because of high chemical stability, broad and intense charge transfer (CT) band arising from MoO 4 tetrahedron unit in the near UV region and the capability of efficiently capturing radiation from a GaN based LED [3]. Intra configurational f–f transitions of trivalent europium (Eu 3? ) ions resulting in the red lumi- nescence are of technological importance [4]. CaMoO 4 : Eu 3? is a potentially attractive candidate as a superior red phosphor because of its efficient absorbtion under near-UV excitation, satisfactory chromaticity coordinates and excellent stability [5]. Many works were reported on the improvement of luminescent properties of CaMoO 4 :Eu 3? phosphors by various charge compensation using Li ? ,K ? , Na ? etc. and by codoping of ions like Bi 3? [6–8]. Quantum efficiency of CaMoO 4 :Eu 3? was reported to be 12.78 and 21–23 % via hydrothermal synthesis and sol–gel reaction routes respectively [9, 10]. However, its red emission intensity and quantum efficiency still needs to be improved at the application point of view. As the luminescent per- formance of Eu 3? is deeply affected by the crystal field factors such as structural distortion and symmetry, the incorporation of slightly smaller ions like Zr 4? and Si 4? in place of Ca 2? and Mo 6? ions may result in some structural adjustment enhancing the red emission. Substitution of the Ca 2? site with Eu 3? ions results in a net positive charge. In general, the positive charges can be compensated by either cation vacancies or oxygen interstitials [11]. Substitution of Zr 4? in the Ca 2? site creates a more positive charge effect in the A site which alters the environment around the luminescent Eu 3? in turn affecting the luminescence T. L. Francis  P. P. Rao (&)  S. K. Mahesh  V. R. Reshmi Materials Science and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology (NIIST), Trivandrum 695019, India e-mail: padala_rao@yahoo.com M. Thomas Department of Physics, St. Therasa’s College, Ernakulam 682011, Kerala, India 123 J Mater Sci: Mater Electron DOI 10.1007/s10854-014-1892-4