Er 3+ /Yb 3+ codoped LiYF 4 nano/microcrystals were controllable synthesized via a facile solvothermal method. Based on the emission spectra and quantum efficiencies under 976 nm pumping, size-dependent upconversion luminescence was studied.
Lanthanides doped fluoride nanoparticles have been extensively studied for their potential applications in bio-imaging, display, etc [1][2]. Due to the smaller size, nanocrystals were also used in optical devices. For example, LaF 3 :Nd 3+ nanoparticle doped polymethyl methacrylate (PMMA) composites were successfully used for the preparation of waveguides with the optical gain of 18 dB [3]. However, the conventional polymer host, PMMA, does not show excellent transparency properties in the infrared region, especially in the telecommunication window. In this work, we report the synthesis and optical properties of Er 3+ -doped LiYF 4 −bisphenol A ethoxylate diacrylates (BPAEDA) nanocomposite. The polymer BPAEDA showed broad transparency range centered at 1550 nm which is confirmed by the absorption spectrum. Under the excitation of a 978 nm laser, the optically transparent Er 3+ -doped LiYF 4 −BPAEDA nanocomposite showed intense and broad emissions in S+C+L band.Using the solvothermal method, we synthesized Er 3+ -doped LiYF 4 nanocrystals with the average size of 16 nm as shown in Fig. 1(a). The as-synthesized nanocrystals were well separated. The XRD pattern of the nanocrystals was shown in Fig. 1(b). The diffraction peaks could be indexed to the standard data of tetragonal LiYF 4 (JCPDS 77-816). Because the oleic acid was used in the preparation procedure, the surface of nanocrystals was modified by the oleate ligand which is necessary for dispersing nanocrystals in some solvents such as chloroform. The chloroform colloid containing Er 3+ -doped LiYF 4 nanocrystals was added into the chloroform diluted liquid BPAEDA monomer. After the addition of initiator azobisisobutyronitrile (AIBN), the monomer containing LiYF 4 nanocrystals was carefully heated at 60 C for polymerization. Figure 1(c) shows the optically transparent composite of BPAEDA polymer containing LiYF 4 : 1%Er 3+ nanocrystals (1% v/v) of 16 nm. Fig. 1 (a) the TEM image and (b) the XRD pattern of the as-synthesized LiYF4: 1%Er 3+ nanocrystals; (c) The transparent composite of LiYF4: 1%Er 3+ −BPAEDA.Fig. 2 The emission spectra of BPAEDA composites (1% v/v) containing LiYF4: x%Er 3+ nanocrystals (x=1, 2, and 5) under the excitation of a 978 nm laser.Under the excitation of a 978 nm laser, the as-prepared nanocomposite showed broad emission band centered at 1550 nm, as shown in Fig. 2. LiYF 4 nanocrystals with different Er 3+ concentrations were used for the nanocomposite. All the composited were doped with the same concentration of the nanocrystals (1% v/v). It is obvious that the BPAEDA composite doped with LiYF 4 : 5%Er 3+ nanocrystals showed stronger relative emission intensity. In all the composites with different Er 3+ concentrations, the width of the emission is about 140 nm (1480-1620 nm) which covers the S+C+L band. The emission in S and C band range is strong and in L band is relatively flat. The relative emission intensity of the nanocomposite could be changed, if the doping amount of nanocrystals increases. Under a suitable doping concentrati...
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