Microwave-Employed Sol–Gel Synthesis of Scheelite-Type Microcrystalline AgGd(MoO4)2:Yb3+/Ho3+ Upconversion Yellow Phosphors and Their Spectroscopic Properties

Chang Sung Lim,Victor Atuchin,Maxim Molokeev,Aleksandr Oreshonkov,Aleksandr Aleksandrovsky

doi:10.3390/cryst10111000

Abstract

AgGd(MoO4)2:Ho3+/Yb3+ double molybdates with five concentrations of Ho3+ and Yb3+ were synthesized by the microwave employed sol–gel based process (MES), and the crystal structure variation, concentration effects, and spectroscopic characteristics were investigated. The crystal structures of AgGd1−x−yHoxYby(MoO4)2 (x = 0, 0.05; y = 0, 0.35, 0.4, 0.45, 0.5)at room temperature were determined in space group I41/a by Rietveld analysis. Pure AgGd(MoO4)2 has a scheelite-type structure with mixed occupations of (Ag,Gd) sites and cell parameters a = 5.24782 (11) and c = 11.5107 (3) Å, V = 317.002 (17) Å3, Z = 4. In doped samples, the sites are occupied by a mixture of (Ag,Gd,Ho,Yb) ions, which provides a linear cell volume decrease with the doping level increase. Under the excitation at 980 nm, AGM:0.05Ho,yYb phosphors exhibited a yellowish green emission composed of red and green emission bands according to the strong transitions 5F5 → 5I8 and 5S2/5F4 → 5I8 of Ho3+ ions. The evaluated photoluminescence and Raman spectroscopic results were discussed in detail. The upconversion intensity behavior dependent on the Yb/Ho ratio is explained in terms of the optimal number of Yb3+ ions at the characteristic energy transfer distance around the Ho3+ ion.

Highlights

In the last years, rare earth (RE) doped light emitters, based on the frequency upconversion (UC), have been extensively investigated and applied in fields such as optoelectronics as solid state laser devices, display technology, light emitting diode (LED) materials, solar energy cell compositions, and biological imaging sensors [1–4]
All diffraction peaks are obviously indexed by the tetragonal cell (I41 /a) with cell parameters close to those of AgEu(MoO4 )2 [36] and NaGd(MoO4 )2 [37]
These crystal structures were taken as a starting model in Rietveld refinement

Summary

Introduction

Rare earth (RE) doped light emitters, based on the frequency upconversion (UC), have been extensively investigated and applied in fields such as optoelectronics as solid state laser devices, display technology, light emitting diode (LED) materials, solar energy cell compositions, and biological imaging sensors [1–4]. In UC phosphors, the conversion of near infrared photons to visible photons is reached via a multiphoton absorption process, and finely crystallized host materials are needed to decrease energy losses in multistage electronic transitions. Among such crystals, RE-containing molybdates are widely investigated in terms of searching for new structures, including structure-modulation effects, promising spectroscopic characteristics, and excellent UC photoluminescence (PL) properties [5–12]. RE-containing molybdates are widely investigated in terms of searching for new structures, including structure-modulation effects, promising spectroscopic characteristics, and excellent UC photoluminescence (PL) properties [5–12] In this aspect, binary RE-containing tetragonal molybdates of general composition ARE(MoO4 )[2] The complex ST molybdates are extensively investigated as host materials in the phosphor preparation and laser technology, respectively [13–24]

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Results

Conclusion