Journal of Alloys and Compounds
Synthesis and spectroscopic properties of RbLa1ÀxEuxP4O12 nanocrystals
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L. Marciniak , M. Stefanski, R. Tomala, D. Hreniak, W. Strek
Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-422 Wroclaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The cubic and monoclinic RbLa1ÀxEuxP4O12 nanocrystalline phosphors were synthesized using co-precip-
itation method. The influence of the dopant concentration on the structural and luminescent properties
was investigated. The concentration of Eu3+ ions has strong impact of the emission spectra, luminescence
decay profiles and charge transfer bands. The concentration effect was discussed in term of changes of the
Eu3+ local symmetry associated with the differences of the La3+ and Eu3+ ionic radii.
Ó 2014 Elsevier B.V. All rights reserved.
Received 1 September 2014
Received in revised form 28 October 2014
Accepted 31 October 2014
Available online 14 November 2014
Keywords:
Tetraphosphates
Europium
Rubidium phosphates
Nanocrystals
1. Introduction
The phosphates doped lanthanides are especially attractive for
luminescent organic/inorganic composites [7–9].
The crystal of methaphosphates doped with rare earth ions
places important role in the field of optics and laser applications.
Especially Nd3+ based tetraphosphates have attracted great atten-
tion due to reduced concentration quenching of the luminescence
with maintaining good mechanical and chemical stability. The
laser experiments on LiNdP4O12 crystal were already reported in
80s of XX century. Since that moment many papers were published
concerning its optical properties. The unique optical properties are
associated with long distance between Nd3+ ions (above 5.6 A)
what posses strong impact on the concentration quenching effect.
Moreover the NdO8 dodecahedrons are well separated to each
other by PO4 tetrahedron what additionally reduces interionic
energy transfers.
The group of alkali ion tetraphosphates consists of 5 members
LiLaP4O12, NaLaP4O12, KLaP4O12, RbLaP4O12 and CsLaP4O12. Since
the first three of them are constitute of helical chains of (PO4)À
groups the RbLaP4O12 is constructed of P4O12 rings. Hence the dif-
ferences in structural and optical properties of this host. However
there are many papers concerning spectroscopic properties of LiL-
nP4O12 and KLnP4O12 host relatively small amount of studies have
been performed for RbLnP4O12 host. Horchani et al. [1–3] reported
spectroscopic properties of RbPrP4O12 crystals for scintillating
applications. The electronic and optical properties of RbHoP4O12
crystals were examined by Zhu et al. [4]. The synthesis and
structural studies of RbLnP4O12 and RbYbP4O12 crystals were
reported by Byrappa and Litvin [5] and Zhu et al. [6] respectively.
Recently we have reported optical studies of LiLa1ÀxNdxP4O12
nanocrystals [10–12], LiLa1ÀxDyxP4O12 nanocrystals [13] and
La1ÀxNdxP5O14 nanocrystals [14]. Nevertheless from the best of
our knowledge any studies concerning luminescence properties
of RbLnP4O12 nanocrystals were not already reported. In this paper
the structural and optical properties of monoclinic and cubic
structures of RbLa1ÀxEuxP4O12 nanocrystals are investigated.
2. Experimental
RbLaP4O12 was successfully prepared by precipitation method. Rubidium car-
bonate (Rb2CO3, Alfa Aesar, 99.8%), lanthanum oxide (La2O3, Stanford Materials
Company, 99.999%), ammonium diphosphate (Aldrich, P99.99%) and europium
oxide (Eu2O3, Stanford Materials Company, 99.99%) was used as raw materials. Stoi-
chiometric amounts of starting materials were weighted. Rb2CO3, La2O3 and Eu2O3
were dissolved in nitric acid at 120 °C and re-crystallized at least three times. Sub-
sequently re-crystallized solution of rubidium ions was added to also re-crystal-
lized solution of lanthanides and then the whole was mixed with solution of
ammonium diphosphate. In result, obtained suspension was placed in laboratory
dryer at 90 °C for at least two days. Finally, the sample was annealed for 6 h at tem-
peratures from range 300–1100 °C in the muffle furnace.
The powder diffraction studies were carried out on PANalytical X’Pert Pro dif-
fractometer using Ni-filtered Cu Ka radiation (V = 40 kV, I = 30 mA). The average
grain size was determined using Rietveld refinement technique. Emission and exci-
tation spectra were measured using FLS980 Fluorescence Spectrometer from Edin-
burgh Instruments equipped with 450 W Xenon lamp. Both the excitation and
emission 300 mm focal length monochromators were in Czerny Turner configura-
tion. Excitation arm was supplied with holographic grating of 1800 lines/mm,
blazed at 250 nm. All presented spectra were corrected on the detector sensitivity
and lamp characteristic. The luminescence kinetics measurements were performed
using Jobin-Yvon HR1000 monochromator equipped with 928 photomultiplier from
Hamamatsu. The decay profiles were collected using a LeCroy WaveSurfer 400
oscilloscope.
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Corresponding author.
0925-8388/Ó 2014 Elsevier B.V. All rights reserved.