Broadband infrared luminescence of Cr 3+ -doped LiInSiO 4 phosphors
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Cr3+-doped LiInSiO4 phosphors were prepared by a solid-state reaction method. X-ray diffraction measurement was carried out for crystalline phase identification. Absorption, photoluminescence, excitation, and time-resolved spectra were measured to investigate the optical properties of the phosphors. Two broadband near-infrared emissions centered at 920 and 1172 nm were observed. Time-resolved spectra show that the emission at 1172 nm decays more quickly than the emission at 920 nm. The electron spin resonance spectra exhibit a broad resonance signal at g = 1.96 because of exchange-coupled Cr3+ pairs. The value of Dq/B for low and intermediate crystal fields was evaluated. We suggest that Cr3+ incorporated into different octahedral sites of the crystal is responsible for the different near-infrared luminescence.
I. INTRODUCTION
Luminescent materials doped with isolated active centers find great applicability in displays, lighting, lasers, optical telecommunications, and various other fields.1–3 With the rapid development of technology, demands in these fields cannot be well satisfied, and they present new challenges for traditional phosphors. One of the challenges in communication technology is the limited gain bandwidth of rare-earth-doped optical fiber amplifiers, and great efforts have been made to solve this problem by many research groups in the last decade.4–6 Since the number of transmission channels depends on the gain bandwidth of the amplifier and the laser source, broadband amplifiers and tunable laser sources covering from 1.3 to 1.6 mm is one of the key points to accomplish optical communication of the low loss silica fiber in the whole telecommunication window. Recently, transitionmetal-doped crystals have attracted great interest because of the broadband luminescence in the near-infrared (NIR) region.7–10 Bismuth, nickel, and chromium-doped materials all show potential application for broadband fiber amplifiers, and there have been extensive investigations on the NIR luminescent properties of related phosphors. Recently, olivine crystals have attracted great attention.11–13 Taking LiIn(Ge/Si)O4 as an example, it is reported that there are two major types of sites in the olivine structure. When chromium was doped, Cr4+ may occupy tetrahedral sites replacing Si4+ or Ge4+ in the lattice and Cr3+ occupy octahedral sites replacing Li+ or In3+. Sixfold coordination Cr3+ and fourfold coordinaa)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0026
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http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 2, Feb 2010 Downloaded: 24 Apr 2015
tion Cr4+ show different optical properties. The available range of tunability of all known Cr3+-doped materials is from 700 nm (BeAl2O6) to 1107 nm (La3Ga5SiO14). However, the range of tunability of Cr4+-doped materials is from 1130 nm (Mg2SiO4) to 1628 nm (Y3Sc0.5Al4.5O12).14 Chromium ion in the tetravalent state is widely considered to be the only available valent state for laser operation in the near-infrared region from
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