Time- and Temperature-Dependent Luminescence of Manganese Ions in Ceramic Magnesium Aluminum Spinels.

Nicholas Khaidukov,Maria Brekhovskikh,Guido Toci,Vladimir Makhov,Barbara Patrizi,Angela Pirri,Matteo Vannini

doi:10.3390/ma14020420

Abstract

Samples of magnesium aluminum spinel ceramics doped with manganese ions were prepared by a high-temperature solid-state reaction method; their potential as red-emitting phosphors was analyzed using a time-resolved luminescence spectroscopy technique, from room temperature to 10 K. It was found that in the red spectral range, the luminescence spectra of manganese ions in the MgAl2O4 spinel showed a narrow band peaking at 651 nm due to the emission of Mn4+ and a broader emission band in the region of 675 ÷ 720 nm; the ratio of intensities for these bands depends on the synthesis conditions. By applying a special multi-step annealing procedure, the MgAl2O4:Mn4+ phosphor containing only tetravalent manganese ions, Mn4+, was synthesized. Broad-band far-red emission observed from MgAl2O4:Mn and Mg1.25Al1.75O3.75F0.25:Mn phosphors, prepared by a conventional method of a solid-state reaction, was interpreted as coming from Mn3+ ions.

Highlights

At present, the development of phosphors for application in phosphor-converted white Light Emitting Diodes is one of the most relevant areas of research in lighting technologies
One more spinel-structured ceramics doped with manganese ions was prepared by using the mixture of sample II, MgO and MgF2 in weighed amounts corresponding to the composition of Mg1.25 Al1.75 O3.75 F0.25
The obtained low-temperature and time-resolved features of the red emission band characterizing the PL spectrum of the Mn4+ -doped MgAl2 O4 sample confirmed the generally accepted model of this luminescence as caused by the Mn4+ 2 E → 4 A2 transitions, including the zero-phonon line (ZPL) located at 651 nm and the Stokes and anti-Stokes vibronic side-bands, which are broadened by the cation disorder caused by inversion in the spinel crystal structure

Summary

Introduction

The development of phosphors for application in phosphor-converted white Light Emitting Diodes (pc-WLEDs) is one of the most relevant areas of research in lighting technologies. Since the introduction of the first commercial pcWLEDs, a search for new efficient red light-emitting phosphors has been actively ongoing. A significant contribution in the red region of the emission spectrum is highly required to obtain warm white light from pc-WLEDs based on the standard technology exploiting the combination of a blue LED chip and a converting yellow YAG:Ce3+ -type phosphor [1]. A suitable phosphor should have significant absorption in the blue spectral range and emit in the red (i.e., in the 620 ÷ 650 nm range) [2]. In most commercial pc-WLEDs, some nitride compounds doped with Eu2+ rare earth ions are used as red phosphors [3].

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Conclusion