Luminescence of KCaSO4Cl:X, Y (X=Eu or Ce; Y=Dy or Mn) halosulfate material

doi:10.1016/j.jlumin.2011.03.042

Journal of Luminescence

Volume 131, Issue 8, August 2011, Pages 1612-1616

https://doi.org/10.1016/j.jlumin.2011.03.042 Get rights and content

Abstract

Polycrystalline KCaSO₄Cl:Eu, Dy, KCaSO₄Cl:Ce, Dy and KCaSO₄Cl:Ce, Mn phosphors prepared by a solid state diffusion method have been studied for its photoluminescence (PL) characteristics. The presence of two overlapping bands at around 400 and 450 nm in the PL emission spectra of the phosphor suggests the presence of Eu²⁺ in the host compound occupying two different lattice sites. The effects of co-doping on the photoluminescence (PL) characteristics of KCaSO₄Cl:Eu or Ce phosphors have been studied. The decrease in peak intensity of the phosphor on co-doping it with Dy gives an insight into the emission mechanism of the phosphors, which involves energy transfer from Eu²⁺→Dy³⁺, Ce³⁺→Dy³⁺ and Ce³⁺→Mn²⁺.

Highlights

► A new KCaSO₄Cl host is invented as a luminescent material. ► Present phosphors can be useful in scintillation, TL dosimetry as well as in lamp industry. ► Polycrystalline KCaSO₄Cl:Eu, Dy; Ce, Dy and Ce, Mn have been studied for its PL characteristics. ► Effects of Dy and Mn co-doping on the PL characteristics of KCaSO₄Cl:Eu or Ce have been studied. ► An efficient energy transfer from Eu²⁺ to Dy³⁺, Ce³⁺ to Dy³⁺ and Ce³⁺ to Mn²⁺ has been observed.

Introduction

The luminescence properties of co-activator compounds have received considerable interest. The main interest has been received concerned with the utilization of efficient energy migration on sensitizer to activator. Energy transfer phenomena have led to the development of new and efficient photoluminescence materials. The Eu doped solid state materials usually show strong broadband luminescence with a short decay time of the order of some tens of nanoseconds. Luminescence is very strongly dependent on the host lattice and can occur from the ultraviolet to the red region of the electromagnetic spectrum. Eu emission is intense enough to find important industrial applications in, for example, the tricolor low-pressure mercury fluorescence lamps.

Luminescent materials are used for various purposes such as making lamps [1], [2], [3], CR tubes and TV screens [4], electroluminescent lamp and display panels, LEDs, detectors for X-ray imaging [5], [6], [7], [8], scintillation detectors [9], laser crystals [10], paints [11] and solar concentrators [12]. The luminescent properties of Eu³⁺ compounds obtained in the presence of Eu²⁺ are of considerable interest in recent years.

Eu²⁺ emission results from two types of transitions. The most common is that due to 4f⁶5d→4f⁶ (⁸S_7/2). As the position of the band corresponding to 4f⁶5d configuration is strongly influenced by the host, the emission can be anywhere from 365 nm (e.g. in BaSO₄) to 650 nm (e.g. in CaS). Blasse [13] has listed the Eu²⁺ doped compounds, which shows that the emission color of Eu²⁺ can vary in a broad range, from ultraviolet to red. Since the 4f→5d transition is an allowed electrostatic dipole transition, the absorption and emission of Eu²⁺ are very efficient in many hosts, which makes the Eu²⁺ doped phosphors of practical importance.

CaF₂:Mn does not give any fluorescence under the UV excitation while CaF₂:Ce gives a characteristic Ce³⁺ fluorescence emission with UV light excitation .The combination of Ce and Mn in the CaF₂ lattice however gives brilliant Mn²⁺ fluorescence emission in addition to that of Ce³⁺ on UV excitation due to energy transfer from Ce³⁺ to Mn²⁺ ions. Similar enhancement in the fluorescence efficiency of Dy and Mn ions was reported in CaSO₄:Ce, Dy and CaSO₄:Ce, Mn [10]. However, the application of a similar energy transfer mechanism leading to enhanced sensitivity in the case of thermoluminescence (TL) and photoluminescence (PL) is made continuously. During the course of the present investigation on TL in sulfate based phosphors, we have reported several sulfate phosphor possessing properties useful for TL dosimetry of ionizing radiations [14], [15], [16], [17], [18], [19].

Energy transfer from donor to acceptor plays an important role in luminescence and solid state lasers. It is important to get different regions of the visible spectrum in a matrix in which different activation ions can be structurally for cation sites. In recent years there has been a growing interest in stoichiometric sulfate compounds as host lattices for efficiently transporting excitation energy from a sensitizer to an activator. This has resulted in the production of new and efficient photoluminescent materials.

In recent years Moharil and co-workers [20], [21], [22], [23] have reported several phosphors on rare earth (RE) ions doped mixed sulfate. Other than sulfates and mixed sulfates, some investigations are going in progress on halosulfate-based materials. Klement [24] synthesized the halosulfate Na₆Ca₄(SO₄)₆F₂ and characterized this compound by X-ray powder diffraction (XRD), and also the compounds Na₆Pb₄(SO₄)₆Cl₂ [25], [26], Na₆Cd₄(SO₄)₆Cl₂ [27] and Na_6.45Ca_3.55(SO₄)₆ (F_xCl_1–x)_1.55 [28]. Recently we have reported new halosulfate phosphors [29], [30]. The luminescence properties and energy transfer of KZnSO₄Cl:Ce, Dy and KMgSO₄Cl:Ce, Dy has been studied.

Section snippets

Experimental

The samples KCaSO₄Cl (pure and doped) were prepared by a solid state diffusion method. While preparing KCaSO₄Cl:Eu, Dy, KCaSO₄Cl:Ce, Dy and KCaSO₄Cl:Ce, Mn the constituents KCl, CaSO₄ and sulfate salt of europium and dysprosium were taken in a stoichiometric ratio and crushed in a crucible for 1 h. Then this material was heated at 800 °C for 8 h, resulting in the compound of KCaSO₄Cl:Eu, Dy in powder form. The samples were then slowly cooled at room temperature. The resultant polycrystalline mass

XRD and particle size

Fig. 1 shows the X-ray diffraction (XRD) pattern of KCaSO₄Cl material. The XRD pattern did not indicate the presence of the constituents CaSO₄ or KCl and other likely phases, which is an indirect evidence for the formation of the desired compound. These results indicate that the final product was formed in homogeneous form.

When materials are less than approximately 100 nm in size, appreciable broadening in the X-ray diffraction lines occurs. The observed line broadening can be used to estimate

Conclusion

It can be concluded from the results presented and discussed here that in the present material the dopant ions Eu²⁺ instead of giving a single emission peak at around 450 nm, as in the case of the conventional material, give two bands at around 400 and 450 nm. Since the 450 nm emission in the PL may be an indicator of good TL material. In KCaSO₄Cl matrix singly Dy doped emission is not observed. Eu²⁺ plays an important role in PL emission in the host lattice, which could be attributed to the

Acknowledgment

We are thankful to University Grant Commission (UGC), New Delhi, for financial support.

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Citation Excerpt :
The compounds Na6Pb4(SO6)4Cl2 (Caracolite) [19] Na6Cd4(SO6)4Cl2 [20], Na6Ca4(SO6)4Cl2 (Cesanite) [21,22] are known as members of the halogen group. We have reported Na21Mg(SO4)10Cl3, K3Ca2(SO4)3F, KMgSO4F, KCaSO4Cl, KMgSO4Cl, and Na6(SO4)2FCl [23–29] new inorganic materials as halophosphors. There is no any literature or information available on photoluminescence in KMgCl3 compound.
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Citation Excerpt :
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Journal of Luminescence

Abstract

Highlights

Introduction

Section snippets

Experimental

XRD and particle size

Conclusion

Acknowledgment

References (35)

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J. Phys. D

Prog. Cryst. Growth Char. Mater.

Prog. Q. Ele.

Pigment Handbook

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Lumin. Inorg. Solids

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