Luminescence Properties of Gd2(MoO4)3 Modified with Sm(III) and Tb(III) for Potential LED Applications

Martin Tsvetkov,Denitsa Elenkova,Maria Milanova

doi:10.3390/cryst12010120

Abstract

Light-emitting phosphors, doped with lanthanide ions of Tb(III) and Sm(III) of the type Gd1.97−y SmyTb0.03(MoO4)3 (y = 0.01–0.11, step 0.02) and Gd1.95−xSm0.05Tbx(MoO4)3 (x = 0.01–0.09, step 0.02), were synthesized and characterized by X-ray diffraction, UV-Vis spectroscopy, scanning and transmitting electron microscopy (SEM, TEM) as well as photoluminescence spectroscopy. The effect of the doping content of Tb/Sm was followed. The unit cell parameters for Gd1.97−ySmyTb0.03(MoO4)3 and Gd1.95−xSm0.05Tbx(MoO4)3 changed with the increase in the Tb/Sm content. The microstrain values also increased, proposing an increased concentration of defects. The mean particle size was estimated to be approximately 0.6 µm. Based on a Williamson–Hall plot, the size of the crystallites was determined to be in the range of 42–60 nm for modified and pure Gd2(MoO4)3 samples, respectively. The samples excited at 406 nm exhibited characteristic emission lines of Sm (485, 555, 646 nm). The host material Gd2(MoO4)3 emission in visible light was explained by the crystal structure defects, namely, oxygen vacancies. The CIE x/y color coordinates of the phosphors were determined and the related points were located in the green-yellow/pale yellow region of the visible light. The excited state lifetimes were determined for both groups of the samples, showing values in the millisecond range and indicating the samples as promising phosphors.

Highlights

Phosphors modified with rare earth elements have been of great interest in the last few decades due to their potential applications in various fields such as displays, LEDs, optical fibers, sensors, secret inks and biochemical markers [1]
The most popular method for making white LEDs is the combination of a blue LED (InGaN) with yellow phosphor Y3Al5O12: Ce (YAG:Ce), as white light can be obtained by combining blue and yellow emissions. Such wLEDs suffer from insufficient radiation in the red area, which leads to a low color rendering index and a high radiation temperature (7000 K: blue-white light) [3]
It is known that the molybdates of the middle lanthanides crystalize in a monoclinic Eu2(WO4)3-type (C2/c) (α-polymorph) structure [22]

Summary

Introduction

Phosphors modified with rare earth elements have been of great interest in the last few decades due to their potential applications in various fields such as displays, LEDs, optical fibers, sensors, secret inks and biochemical markers [1] In addition to their excellent optical properties, the materials based on rare earth elements are thermally [2] and chemically stable [1]. The most popular method for making white LEDs (wLED) is the combination of a blue LED (InGaN) with yellow phosphor Y3Al5O12: Ce (YAG:Ce), as white light can be obtained by combining blue and yellow emissions Such wLEDs suffer from insufficient radiation in the red area, which leads to a low color rendering index and a high radiation temperature (7000 K: blue-white light) [3]. Among the matrices suitable for the incorporation of lanthanide ions for LEDs, application oxides [4], fluorides and oxofluorides [5], molybdates [6,7], tungstates [8], vanadates and phosphates [9,10] have been studied

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