Preparation, characterization and luminescent properties of red-emitting phosphor: LiLa2NbO6 doped with Mn4+ ions

https://doi.org/10.1016/j.jallcom.2018.04.295Get rights and content

Highlights

  • We provide a comprehensive study of the luminescence mechanism of the Mn4+ ion.

  • Sharp emission lines belong to vibrational modes are observed at low temperature.

  • The LiLa2NbO6:Mn4+ phosphor shows special anti-thermal stability at low temperature.

Abstract

Series of Mn4+-activated LiLa2NbO6 red emitting phosphors were prepared by the solid state method. The structural and luminescence properties are investigated on the basis of X-ray diffraction (XRD), emission and excitation spectra, and luminescence decay curves. The LiLa2NbO6:Mn4+ phosphors can be efficiently excited by near-UV to blue light and exhibit bright red emission at around 712 nm, which can be assigned to the 2Eg4A2g transition of the 3 d3 electrons in [MnO6] octahedra. Temperature dependent emission spectra and decay curves from 10 to 480 K are analyzed to understand the luminescence mechanism of Mn4+ in LiLa2NbO6 lattice. Notably, such a novel red emitting phosphor shows special anti-thermal quenching behavior.

Introduction

Recently, more attentions have been paid to phosphors doped with transition metal ions with 3 d3 electronic configuration. Typically, red-emitting Mn4+ is related to several vibrational sidebands, which are influenced by covalency and coordination symmetry. Therefore, optical properties of Mn4+ are closely related to the host matrix [1]. Generally, Mn4+ ions can only be accommodated and stabilized in an octahedral lattice site of the host crystals, such as including AlO6, NbO6, TiO6, SiO6, AlF6, TiF6, SiF6, GeF6 octahedron and so on, with broad absorption spectrum in the range of 220–600 nm and show red-emitting within the range 600–780 nm [2].

As previously reported, Mn4+-doped luminescence materials can be divided into two categories: Mn4+-doped fluorides and Mn4+-doped oxides. The Mn4+-doped fluorides, e.g., K2SiF6 and K2TiF6 [3], BaGeF6 [4], usually show sharp red emission with peaks at around 630 nm. The Mn4+ luminescence in fluoride lattices has been patented for use in white light generating phosphor blends in LED devices [3]. While, Mn4+-doped oxides, e.g., CaAl12O19 [5], Ca14Zn6Al10O35 [6], and CaMg2Al16O27 [1], usually exhibit deep red emission at around 700 nm. Such materials can be used as potential candidates for holographic recording and optical data storage [7,8], laser application [9], and thermoluminescence dosimetry [10]. Regretfully, fluoride hosts are unstable in environment. Moreover, the toxic HF solution used during the fluoride synthesis process is harmful to human living condition and health. As an alternative, Mn4+-activated oxides are more favorable because of their high chemical stability and ecofriendly preparation procedure. On the other hand, in the past few years, a large amount of novel Mn4+-activated red emitting fluorides or oxides phosphors have been developed. For example, a novel deep red-emitting phosphor KMgLaTeO6:Mn4+ used in w-LEDs is reported, which can be efficiently excited with UV or blue light with a high quantum yield of 68.9% upon 365 nm excitation [11]. Rb2TiF6:Mn4+ was prepared by the ion exchange method with high thermal stability and thermal quenching resistance with excellent color stability [12]. However, few works focused on the luminescent mechanism of Mn4+ doped oxide phosphors. To explore new kinds of candidates, more deep investigations on the luminescent mechanism are necessary.

The purpose of the current work is to provide a comprehensive study of the luminescence mechanism of the Mn4+ ion in the LiLa2NbO6 lattice with octahedral NbO6 emitting center. In addition, Li congaing neonates are very sensitive to the intrinsic defects which may improved the optical properties of LiLa2NbO6:Mn4+ red emitting phosphors [13]. In this work, LiLa2NbO6:Mn4+ were synthesized via the solid state method, and then the luminescence properties are characterized in detail by temperature-dependent photoluminescence excitation, emission spectra and decay curves.

Section snippets

Synthesis of LiLa2Nb1-xMnxO6 (0.005 ≤ x ≤ 0.01)

A series of LiLa2Nb1-xMnxO6 (0.005 ≤ x ≤ 0.01) phosphors were prepared by the conventional high-temperature solid-state reaction. The raw materials during the synthesis process are Li2CO3, La2O3, Nb2O5 and MnO2 in analytical reagent. Based on the formula of LiLa2Nb1-xMnxO6 (0.005 ≤ x ≤ 0.01), required amounts of the raw materials were calculated and weighted exactly by an electronic balance, and then thoroughly ground for at least 30 min. To compensate the loss of lithium during the sintering

Phase formation and crystal structure

Fig. 1 shows the XRD patterns of the LiLa2Nb1-xMnxO6 (0.005 ≤ x ≤ 0.01) red phosphors along with the standard PDF card (JCPDS No. 40-0895) for comparison. All the XRD patterns match well with the standard PDF card and no traces of impurity phases are observed. The LiLa2NbO6 crystal is built up of alternating strands of LiO6 and slightly disordered NbO6 with La3+ locating in the cavities of the interconnected network [14]. Based on requirements of the radius similarity and the charge balance

Conclusions

Here we investigate the luminescence properties of LiLa2NbO6:Mn4+ red emitting phosphors in the temperature range 10–480 K. The obtained spectroscopic properties are compared with the Mn4+ in other oxides and fluorides. Concentration dependent excitation and emission spectra were measured and the optimum doping concentration of Mn4+ in LiLa2NbO6 lattice was 0.7 mol%.

It's worth noting that the sharp emission lines corresponding to the local vibrational modes of Mn4+ ions in the LiLa2NbO6 lattice

Acknowledgements

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1D1A1B03029432).

References (44)

  • Q.Y. Shao et al.

    Temperature dependent photoluminescence properties of deep-red emitting Mn4+-activated magnesium fluorogermanate phosphors

    J. Alloys Compd.

    (2013)
  • B. Wang et al.

    CaMg2Al16O27:Mn4+-based red phosphor: a potential color converter for high-powered warm W-LED

    ACS appl. Mater. Int.

    (2014)
  • Q. Zhou et al.

    Mn2+ and Mn4+ red phosphors: synthesis, luminescence and applications in WLEDs, A review

    J. Mater. Chem. C

    (2018)
  • H.M. Zhu et al.

    Highly efficient non-rare-earth red emitting phosphor for warm white light-emitting diodes

    Nat. Commun.

    (2014)
  • Q. Zhou et al.

    A new red phosphor BaGeF6:Mn4+: hydrothermal synthesis, photo-luminescence properties, and its application in warm white LED devices

    J. Mater. Chem. C.

    (2015)
  • K. Seki et al.

    Novel deep red emitting phosphors Ca14Zn6M10O35:Mn4+ (M= Al3+ and Ga3+)

    Chem. Lett.

    (2014)
  • M.A. Noginov et al.

    Spectroscopic studies of Mn4+ ions in yttrium orthoaluminate

    J. Opt. Soc. Am. B

    (1999)
  • G.B. Loutts et al.

    Manganese-doped yttrium orthoaluminate: a potential material for holographic recording and data storage

    Phys. Rev. B

    (1998)
  • Y. Zhydachevskii et al.

    Photoluminescence studies of Mn4+ ions in YAlO3 crystals at ambient and high pressure

    J. Phys. Condens. Matter

    (2006)
  • K. Li et al.

    A novel deep red-emitting phosphor KMgLaTeO6:Mn4+ with high thermal stability and quantum yield for w-LEDs: structure, site occupancy and photoluminescence properties

    Dalton Trans.

    (2018)
  • I.V. Kityk et al.

    Nonstoichiometric defects and optical properties in LiNbO3

    J. Phys. Chem. B

    (2001)
  • R.D. Shannon

    Radii for all species

    Acta. Cryst. A

    (1976)
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