Effect of Sm3+ and Mn2+ incorporation on the structure and luminescence characteristics of Zn2SiO4 phosphor

https://doi.org/10.1016/j.radphyschem.2020.109329Get rights and content

Highlights

  • Zn2SiO4:Sm3+;Mn2+ nanocrystalline phosphor was synthetized by gel combustion method.

  • Crystal structure and morphology were evaluated by XRD, SEM and EDS analyses.

  • Luminescence properties were discussed using PL and TL methods.

  • Overlapped TL peaks behavior were evaluated using IR (with TM - Tstop analysis) and CGCD methods.

  • The causes of the decrease in the activation energy with increasing temperature were physically explained.

Abstract

To evaluate the dopant effect precisely, X-ray diffraction (XRD) for structural, scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS) analysis for morphological, photoluminescence (PL) and thermoluminescence (TL) characteristics of un-doped, 2.0 mol% Sm3+ doped and 2.0 mol% Sm3+;x mol% Mn2+ (x = 0.5, 1.0, 2.0, 4.0) doped Zn2SiO4 phosphors were tested. PL mechanisms of excitation and emission were discussed together with data on the structure and morphology of the samples. The beta doses from 0.1 to 500 Gy with various steps were applied to observe the glow curve readouts after 200 °C preheat at a linear heating rate of 2 °C/s from RT to 500 °C. Zn2SiO4:2.0%Sm3+;0.5%Mn2+ was chosen for further analysis due to having both the most PL and TL peak area. Various heating rate method was used to determine the kinetic parameters as well as initial rise with TM-Tstop analysis and computerized glow curve deconvolution methods.

Introduction

As one of the most useful phosphors, Zn2SiO4 has been widely investigated for more than a century because of its excellent thermal, and chemical stabilities, transparency in the ultraviolet (UV) – visible range, good color purity and high luminescent efficiency with a wide energy gap (5.5 eV) (Ye et al., 2011; Lojpur et al., 2013; Rivera Enríquez et al., 2016; Dubey et al., 2014; Portakal-Uçar et al., 2021). It has been reported that red, blue, and green light output can be dispersed by doping with luminescent centers, transition metal ions, or rare earth elements by providing a wide application area (e.g., novel luminescent materials in cathode ray tubes, lamps, laser crystals, plasma display panels, etc.) (Taghavinia et al., 2006; Zhang et al., 2000; Joly et al., 2007). It is seen that many different qualifications of single or double doped Zn2SiO4 phosphors have been studied in the literature and especially Mn2+ doped Zn2SiO4 phosphors have a considerable place compared to other materials (Ye et al., 2011, 2013; Lojpur et al., 2013; Rivera Enríquez et al., 2016; Dubey et al., 2014; Yan and Huang, 2007; Krasnenko et al., 2020). To change both the optical and electronic features of the host materials, doping any ion(s) may give the possibility when the process is actualized cautiously. Doping may also cause to reduce the efficiency of host materials with new formations since, doping can either result in the formation of new defect centers or recovering of existing levels within the bandgap for defective host materials (Delice et al., 2018). It has been reported that Zn2+ and Mn2+ ions have congruent oxidation states and ionic radius which led Zn2SiO4:Mn2+ phosphor to give a strong green emission from the 4T1(G)→6A1(S) transition. Thus, Mn2+ ions could be well distributed in the Zn2SiO4 host matrix as the substituents of Zn2+ and photoluminescence (PL) of this material is dominantly due to Mn2+ emission while a small amount is based on the emission from the defects that are native to Zn2SiO4 lattice (Lojpur et al., 2013; Selomulya et al., 2003). Contrarily, there are quite a few studies on the structural and luminescence studies of Zn2SiO4:Sm3+ phosphor (Krsmanović Whiffen et al., 2009; Sunitha et al., 2013). Krsmanović Whiffen et al. (2009) stated that Zn2SiO4:Sm3+ phosphor has reddish-orange light consisting of three emission peaks in the visible region near 564, 602, and 649 nm which are assigned to 4G5/26HJ transitions (J = 5/2, 7/2, and 9/2). Besides, thermoluminescence (TL) is an efficient way to probe electronic trap levels in the phosphors by giving an emission of light acquired upon heating the sample after the absorption of energy from the ionizing radiation. To evaluate the dosimetric characteristics of the phosphor requires necessary analysis such as dose response, heating rate effect, reusability, fading, etc. and detailed work includes the estimation of kinetic parameters of the material. Although TL analyzes have been carried out for Mn2+ doped Zn2SiO4 phosphor, there is no detailed TL study for Sm3+ doped sample as we know so far. Recently, our research group argued that the incorporation of Sm3+ ion into Zn2SiO4 phosphor enhances the TL efficiency (Portakal et al., 2019). Un-doped and Sm-doped Zn2SiO4 phosphors were examined and the preliminary TL characteristics were reported including the dose response, reusability, etc. Yet, additional investigations were required because of the inadequate use of Zn2SiO4:Sm observations for dosimetric purposes in TL. The goal of the current study is to examine the TL characteristics of present Zn2SiO4:Sm phosphor by incorporating Mn2+ ion as a co-dopant. The experiment was carried out to determine what the TL and PL characteristics would be when the transition element Mn was doped with the rare earth element Sm. Mn2+ ion which is the most favored ion in terms of its many advantages in different fields was selected to investigate whether it could increase the dosimetric properties of Zn2SiO4:Sm phosphor or not.

There are limited studies concerning the synthesis and luminescence, especially thermoluminescence, analysis of double-doped Zn2SiO4. Although there are quite a number of studies to evaluate the structural, morphological, and luminescence properties of doped Zn2SiO4 phosphor, no study has been conducted on Zn2SiO4:Sm3+;Mn2+. In the present study, x-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive x-ray spectroscopy (EDS), photoluminescence (PL) and TL characteristics of 2.0% Sm3+ and x% Mn2+ (x = 0.5, 1.0, 2.0, 4.0 mol) doped Zn2SiO4 phosphors were tested. Besides, un-doped and only 2.0% Sm3+ doped Zn2SiO4 phosphors were also examined to evaluate the effect of Mn2+ incorporation in detail. The TL characteristics were reported by taking the influence of reusability, heating rate, and dose response on the TL glow curve into account. Kinetic parameters of Zn2SiO4:Sm3+;Mn2+ were evaluated using various heating rates (VHR), initial rise (IR), and computerized glow curve deconvolution (CGCD) methods. Consequently, it was reported whether Sm and Mn incorporated Zn2SiO4 phosphor is a proper candidate for use in TL dosimetry.

Section snippets

Synthesis, structural and morphological characterization

Zn2SiO4 phosphors, un-doped, Sm3+ doped, and Sm3+ and Mn2+ co-doped, were prepared through a gel combustion method. The process was summarized in our previous study in detail (Portakal-Uçar et al., 2021). Additive elements (Sm2O3 (Samarium (III) oxide; 99.99% from Merck) and MnAc2·4H2O (manganese acetate, 99.0% from Merck)) were weighed in stoichiometric ratio if necessary. Acquired powder samples were used for each technique.

PANalytical Empyrean XRD with CuKα radiations (λ = 1.5407 Å) at

Structural and morphological analyses

The XRD patterns shown in Fig. 1 represent the crystal structure of un-doped, Sm3+ doped, and co-doped Zn2SiO4 phosphor with Sm3+ and Mn2+ including the reference pattern. The XRD patterns of all three samples match with the dizinc silicate (O4Si1Zn2) belonging to the R −3 space group in the hexagonal crystal system (ref. code: 98-006-7235) (Hartmann, 1989). The phases related to Sm3+ or Mn2+ dopants were not detected by stating that the ions were well involved in the host lattice. Therefore,

Conclusions

The present study demonstrates; i. the synthesis of Sm3+ and Mn2+ co-doped Zn2SiO4 phosphors prepared through a gel combustion method, ii. their crystal structure and morphology examined by XRD, SEM, and EDS analyses, and iii. luminescence properties using PL and TL methods reported for the very first time. The results mainly highlight the effect of Mn2+ incorporation with different concentrations to Zn2SiO4:2.0%Sm phosphor on the PL and TL properties. Therefore, un-doped and Sm3+ doped Zn2SiO4

Credit author statement

Z.G. Portakal-Uçar: Conceptualization, Methodology, Software, Formal analysis, Writing – original draft. T. Doğan: Data curation, Investigation, Software. S. Akça: Data curation, Investigation, Writing – original draft. Ü.H. Kaynar: Methodology. M. Topaksu: Writing - review & editing, Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

All authors thank Dr. M. Ayvacikli and Prof. Dr. N. Can for their support on XRD and PL evaluations. Z.G. Portakal-Uçar would like to thank Dr. J.M. Kalita and Dr. G.S. Polymeris for the valuable discussions on the TL results. The current study is financially supported by the Research Fund of Çukurova University, Turkey (Project Numbers: FBA-2019-11318 and FAY-2015-435).

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