Luminescence studies and EPR investigation of solution combustion derived Eu doped ZnO

https://doi.org/10.1016/j.saa.2014.04.064Get rights and content

Highlights

  • ZnO:Eu nanopowders have been synthesized by simple low cost SCS method.

  • SEM and TEM images reveal quasi-hexagonal morphology of the samples.

  • ZnO:Eu nanopowders show PL peaks corresponding to both Eu2+ and Eu3+ ions.

  • EPR spectrum exhibits a broad resonance signal attributed to Eu2+ ions.

  • EPR and TL studies reveal native defects. The trap parameters are discussed.

Abstract

ZnO:Eu (0.1 mol%) nanopowders have been synthesized by auto ignition based low temperature solution combustion method. Powder X-ray diffraction (PXRD) patterns confirm the nanosized particles which exhibit hexagonal wurtzite structure. The crystallite size estimated from Scherrer’s formula was found to be in the range 35–39 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies reveal particles are agglomerated with quasi-hexagonal morphology. A blue shift of absorption edge with increase in band gap is observed for Eu doped ZnO samples. Upon 254 nm excitation, ZnO:Eu nanopowders show peaks in regions blue (420–484 nm), green (528 nm) and red (600 nm) which corresponds to both Eu2+ and Eu3+ ions. The electron paramagnetic resonance (EPR) spectrum exhibits a broad resonance signal at g = 4.195 which is attributed to Eu2+ ions. Further, EPR and thermoluminescence (TL) studies reveal presence of native defects in this phosphor. Using TL glow peaks the trap parameters have been evaluated and discussed.

Introduction

Recently, rare-earth (RE) doped II–VI semiconductors have received significant attention due to their applications in optoelectronic devices [1], [2], [3], [4], [5]. The rare earth activated oxide phosphors have good luminescent characteristics, stability in high vacuum, and absence of corrosive gas emission under electron bombardment when compared to currently used sulfide based phosphors. Trivalent RE3+ ions exhibit very sharp and temperature independent RE intra-4f shell transitions, since the 4f shell is well shielded by the outer 5s and 5p electrons. The red-emitting phosphors doped with trivalent RE3+ ions have been widely used in the development of emissive display and tricolor lamp industry.

Europium ion is usually a good choice for many luminescent applications because trivalent europium (Eu3+) is an excellent red activator while divalent europium (Eu2+) can provide efficient blue or green emission under near-ultraviolet excitation. The red 5D07F2 emission of Eu3+ is widely explored in light-emitting devices. The luminescence properties of Eu2+ ions activated materials have been investigated for a long time as efficient blue or green emission in many kinds of commercial phosphors [6], [7].

The use of a semiconductor host enables minority carrier injection to excite RE 4f shell electrons, resulting in 4f shell luminescence. ZnO is a well known direct wide band gap II–VI semiconductor (3.37 eV) which is economical, environmental friendly, and exhibits high thermal and chemical stability [1], [5]. Importantly, it has a large exciton binding energy of 60 meV which is much higher than the thermal energy at room temperature (RT). These properties make ZnO a unique host material for doping with luminescence centers and it can exhibit efficient emission even at or above RT.

ZnO nanostructures have been prepared by several workers employing various synthesis methods such as precipitation [8], spray pyrolysis [9], chemical bath deposition [10], thermal decomposition [11], hydrothermal synthesis [12], sol–gel [13], and solid-state pyrolytic reactions [14]. Solid-state reactions are performed at high temperatures, typically ∼1600 °C, because of the refractory nature of the oxide precursors while in sol–gel and precipitation methods, dilute solutions of metal organics or metal salts are reacted and condensed into an amorphous or weakly crystalline mass. Hydrothermal synthesis is a low temperature and high pressure decomposition technique that produces fine, well-crystallized powders. However, the solid state and sol–gel methods require long processing time and also as-synthesized materials must be heat treated to high temperatures to crystallize the desired phase. Combustion synthesis is a novel technique that has been applied to phosphor synthesis in the past few years. This technique produces highly crystalline powders in the as-synthesized state. The synthesized powders are generally more homogeneous, have fewer impurities, and have higher surface area than other conventional solid-state methods.

As a part of our programme on nanomaterials, here we report europium (Eu) activated zinc oxide nanoparticles prepared by a simple low temperature solution combustion route. The nanopowders are well characterized using different spectroscopy techniques. Electron paramagnetic resonance (EPR), photoluminescence (PL) and thermoluminescence (TL) studies of these phosphors are carried out. In the last few years, TL of ZnO nanostructures have been investigated by several researchers using beta (β) and X-ray irradiation [15], [16], [17]. However, TL studies on ZnO:Eu nanopowders with γ-irradiation are scarce as evident from the literature. Therefore, the present paper intends to investigate the TL properties of γ-irradiated ZnO:Eu nanopowders.

Section snippets

Synthesis

Nano-crystalline ZnO has been prepared using zinc nitrate [Zn(NO3)2] as oxidiser and oxalyl di-hydrazide (ODH) as fuel at a relatively lower temperature (300 °C). The stoichiometry of the redox mixture for combustion is calculated on the total oxidizing and reducing valencies of the oxidizer and the fuel using the concept of propellant chemistry [18]. In undoped ZnO sample preparation, zinc nitrate (5.0 g) and ODH (1.98 g) were dissolved in minimum quantity of double distilled water and heated on

Powder X-ray diffraction (PXRD)

Fig. 2 shows the powder X-ray diffraction (PXRD) profiles of as-formed undoped and Eu doped ZnO nanopowder. The diffraction peaks corresponding to (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0), (1 0 3), (1 1 2) and (2 0 0) directions have been indexed (JCPDS 36-1451) and found to be in hexagonal wurtzite structure. No other impurity peaks are detected which indicate the presence of ZnO nanocrystals without any amorphous component and other additional Eu2O3 crystalline phase. Thus the wurtzite structure is not

Conclusions

The ZnO:Eu (1 mol%) nanopowders were synthesized through a low-temperature solution combustion method using ODH fuel. Hexagonal wurtzite structure without secondary phase was observed from XRD results. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies reveal particles are agglomerated with quasi-hexagonal morphology. Photoluminescence (PL) emission under 254 nm excitation show peaks in regions blue (420–484 nm), green (528 nm) and red (600 nm) which corresponds to

References (35)

  • A.B. Djurisic et al.

    Progr. Quantum Electron.

    (2010)
  • T. Rattana et al.

    J. Alloys Compd.

    (2009)
  • Y. Yang et al.

    J. Cryst. Growth

    (2004)
  • C. Cruz-Vázquez et al.

    Mater. Lett.

    (2007)
  • C. Cruz-Vázquez et al.

    Opt. Mater.

    (2005)
  • A.K. Srivastava et al.

    Opt. Mater.

    (2009)
  • S. Ekambaram et al.

    J. Alloys Compd.

    (1997)
  • Mingya Zhong et al.

    Mater. Chem. Phys.

    (2007)
  • Camellia Panatarani et al.

    J. Phys. Chem. Solids

    (2004)
  • B. Yu et al.

    Mater. Lett.

    (1998)
  • Liqiang Jing et al.

    Mater. Sci. Eng. A

    (2002)
  • C.E. Secu et al.

    Opt. Mater.

    (2009)
  • Y.S. Horowitz et al.

    Nucl. Instr. Meth. Phys. Res. B

    (2001)
  • Dojalisa Sahu et al.

    J. Lumin.

    (2010)
  • K.R. Nagabhushana et al.

    Radiat. Meas.

    (2008)
  • N. Salah et al.

    J. Lumin.

    (2007)
  • U. Ozgur et al.

    J. Appl. Phys.

    (2005)
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