Physics Procedia 2 (2009) 407–409 www.elsevier.com/locate/procedia
Luminescence properties of Pr3+-doped Cs4PbBr6 single crystals Matias Velázqueza,b, Alban Ferriera,c, Stanislas Péchevb, Pierre Gravereaub, Jean-Pierre Chaminadeb, Xavier Portiera and Richard Moncorgéa a
Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP) UMR 6252 CNRS/CEA/ENSICaen, Université de Caen, 6 Boulevard Maréchal Juin, 14050 Caen cedex 4, France b
Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB)
UPR 9048 CNRS, 87 Avenue du Docteur Albert Schweitzer, 33608 Pessac, France c
Institut Franco-Allemand de Recherches de Saint-Louis, 5 rue du Général Cassagnou 68300 Saint-Louis, France
Corresponding authors :
[email protected],
[email protected]
Abstract Centimeter-sized single crystals of pure and Pr3+-doped Cs4PbBr6 were successfully grown using a hightemperature solution (HTS)-based vertical Bridgman-Stockbarger method in silica ampoules sealed under Ar gas. The single crystals are bright orange transparent, non hygroscopic, with a low phonon energy and a wide transparency in the middle infrared (MIR) region. Pr3+ ions can be dissolved into Cs4PbBr6 crystals, resulting in broad MIR absorption bands. We present the characterization of the single crystals by means of Raman, visible, Fourier-transform infrared (FT IR) and emission spectroscopies.
Introduction
There is a growing body of studies focusing on the search, development and spectroscopic investigations of new rare-earth doped and non hygroscopic low phonon energy halide single crystals that could potentially be used as solid state optical amplifiers in middle infrared (MIR) laser cavities [1-8]. Cs4PbBr6 is a long-time known bromide [9] that, among several alkali-based lead bromides, has been investigated in the form of bulk crystals and thin films for its particular optical properties arising from the 6s2 Pb2+ cations electronic outer shell [10,11]. In the course of our experiments, we became interested in doping this material with Pr3+ cations in order to investigate its spectroscopical properties in the 0.4 to 5 Pm spectral range. In this brief report, we detail the optical absorption spectrum in the visible and infrared regions of Cs4PbBr6 crystals doped with Pr3+ ions. In addition, luminescence spectra and excited states dynamics of this new material are reported for the first time.
Results Centimeter-sized single crystals of pure and Pr3+-doped Cs4PbBr6 were successfully grown using a challenging high-temperature solution (HTS)-based vertical Bridgman-Stockbarger method in silica ampoules sealed under Ar gas. Indeed, these crystals melt incongruently, with a peritectic point onset temperature at doi:10.1016/j.phpro.2009.07.025
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Tp=(775.0r1.0) K and a large melting entropy, 'Sp=(11.78r0.87) R, consistent with a faceting of the crystals. The resulting single crystals are bright orange transparent, non hygroscopic, with a low phonon energy and a wide transparency in the middle infrared (MIR) region. In particular, the most energetic Raman active mode lies at ~126 cm-1, entailing in a large infrared transparency domain of the pure Cs4PbBr6 phase extending beyond the detector cut-off wavelength of 24 Pm. Cs4PbBr6 crystallizes at room temperature in the trigonal space group R3c, with a=b=13.7219(2) Å, c=17.3153(3) Å, D=E=90°, J=120° and Z=6. More details about the crystal structure reinvestigation may be found in [12]. Pr3+ ions, which can be dissolved into Cs4PbBr6 crystals from ~7,5 to 9,2.1018 ions.cm-3, give rise to broad MIR absorption bands. The Pr3+:Cs4PbBr6 single crystal room temperature unpolarized MIR absorption cross-section spectrum is displayed in figure 1. The transition bands are poorly structured and the one between 4.5 to 5.3 Pm is fairly broad. The magnitude of the absorption cross-section around 1.5 and 1.9 Pm is 3 to 5 times smaller than that found, for example, by Hömmerich et al. in Pr3+:KPb2Br5 [13]. Assuming that Pr3+ substitutes for Pb2+ in Cs4PbBr6 as in KPb2Br5, the observed discrepancy is likely to be due to the inversion site symmetry characterizing the former. Emission spectra are characterized by wellstructured lines (figure 2), and are associated with long radiative lifetimes (for example W(3P0)=70 µs, W(1D2)=490 µs).
Conclusions It has been established how it is possible to grow pure and Pr3+-doped Cs4PbBr6 single crystals by using a HTS-based vertical Bridgman-Stockbarger method with silica ampoules sealed under Ar atmosphere. The resulting single crystals, typically 1-2 cm long and 5.5 mm wide, are bright orange transparent, non hygroscopic, with a low phonon energy and a large infrared transparency domain. It is finally demonstrated that Pr3+ ions can be dissolved into Cs4PbBr6 crystals resulting in broad and rather weak MIR absorption bands.
1.4 3
P0
Pr3+:Cs4PbBr6
0.75
Density of Pr
3
H4
1.00 3
H4
3
3
3+
18
: 8.8 10
-3
ions cm
3
( H6, F2)
3
( F3+ F4)
0.50
0.25
0.00 1.4
3
F2
1.2
(ICP)
Intensity (Arb. Units)
-20 2 Absorption Cross Section (x10 cm )
1.25
1.0 3+
0.8
Pr :Cs4PbBr6
0.6
Oexc =485nm
0.4
3
0.2
3
3
H6
P0 P1
+
3
F2
3
P1
3
3
P0
F3,4
3
F4
0.0
1.6
1.8 2.0 Wavelength (µm)
2.2
2.4
620
640
660
680
700
720
740
760
Wavelength (nm)
Figure 1: Room temperature unpolarized MIR absorption
Figure 2: Room temperature visible luminescence spectra
cross-section of Pr3+-doped Cs4PbBr6 single crystal. The
of Cs4PbBr6:Pr3+ for a pulse excitation at 485 nm. The inset
inset shows the band assignment on a Pr3+ ion schematic
shows a photo of a Cs4PbBr6:Pr3+ single crystal.
energy level diagram.
M. Vel´azquez et al. / Physics Procedia 2 (2009) 407–409
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