Singular orange emission in Zn 2 SnO 4 :Eu 3+ Santosh K. Gupta a,⇑ , K. Sudarshan a,b , R.M. Kadam a,b a Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India b Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India article info Article history: Received 26 May 2020 Received in revised form 28 July 2020 Accepted 10 August 2020 Available online 12 August 2020 Keywords: Zn 2 SnO 4 Defects Singular emission Luminescence Europium Positron annihilation abstract Considering the positive implication of designing singular emitting phosphor in the area of bioimaging and solid state lighting, this work reports on singular orange emission from Zn 2 SnO 4 :Eu 3+ (ZSOE) phos- phor. The studies showed that ZSOE is stabilized in inverse spinel structure with Eu getting stabilized in octahedral Zn sites with orthorhombic symmetry and D 2h point group leading to very intense orange emission with negligible red component. Undoped Zn 2 SnO 4 (ZSO) on ultraviolet irradiation depicted defect induced blue emission due to synergetic effect of F-centers and vacancy clusters. Ó 2020 Elsevier B.V. All rights reserved. 1. Introduction In many practical applications of phosphors, the purity of the emitted color is extremely critical [1,2]. The orange phosphor with yellow tinge in the range between 585 and 600 nm can be of great relevance to white LEDs and pc-LEDs [3,4] Orange emission in most of the phosphors is achieved by doping Ce 3+ , Mn 2+ or Eu 2+ ion [3–5], but these emissions involve d-electrons and yield extremely broad emission with lower lifetime values. Trivalent Europium doesn’t have these disadvantages, but, Eu 3+ based phosphors yield both the orange as well as the red emission bands at around 590 nm ( 5 D 0 ? 7 F 1 , a pure magnetic dipole transition (MDT) DJ=±1)) and 615 nm ( 5 D 0 ? 7 F 2, a forced electric dipole transition (EDT)), respectively, and are always cross contaminated with each other [6,7]. We have achieved pure singular orange emission with no red contribution either from 615 nm/653 nm peak in Zn 2 SnO 4 microcrystal by simply solid-state diffusion of europium into the lattice. The same could not be achieved in the earlier studies on the nanocrystals of Zn 2 SnO 4 :Eu 3+ [8] probably because of the large distortions around Eu, due to defects in the nanocrystals. 2. Experimental The experimental details are mentioned in S1 (ESI#). 3. Results and discussion The powder X-ray diffraction (XRD) patterns of undoped (ZSO) and Eu-doped Zn 2 SnO 4 (ZSOE) are shown in Fig. S1 (ESI#) and they match well with the pattern corresponding to space group of Fd-3 m. Rietveld fitting of the XRD patterns are shown in Fig. 1a. Zn 2 SnO 4 has inverse spinel structure with half of the Zn and Sn occupying octahedral positions while other half of Zn atoms in tetrahedral positions as shown in Fig. 1b. The fitting yielded unit cell parameter of 8.6591(3) Å in ZSO and is close to 8.657 Å reported by Guo et al. [9]. The Eu doped sample gave marginally smaller lattice constant of 8.6517(3) Å contrary to the increase reported by Dimitrievska et al. [8]from 8.610(2) Å to 8.639(4) Å upon Eu doping in Zn 2 SnO 4 nanoparticles. The minimal influence of doping on the cell constant despite doping of larger Eu 3+ ion sug- gests the relaxation of atoms in the lattice due to creation of charge compensating defects (CCDs). Here, europium can either occupy Zn 2+ or Sn 4+ sites with possible formation of cation or anion vacan- cies as CCDs, respectively. Energy dispersive X-ray spectroscopy (Fig. S2, Table S1) suggested europium doping and its homogenous distribution along with actual composition. 3.1. Emission characteristics of undoped Zn 2 SnO 4 Fig. 2a shows the emission spectra of ZSO under 250 and 300 nm excitation. The emission spectra is similar at both the wavelengths and displayed a very broad blue band spanning the range of https://doi.org/10.1016/j.matlet.2020.128511 0167-577X/Ó 2020 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: santoshg@barc.gov.in (S.K. Gupta). Materials Letters 279 (2020) 128511 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/mlblue