The spectroscopic investigation of ZnWO 4 : Yb 3+ single crystal
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The good quality single crystal ZnWO4:Yb31 was grown by Czochralski method and the spectra were measured. The fluorescence lifetime at 1017 nm was measured to be 644 ls and the radiative lifetime was 209 ls. The laser parameters, bmin Isat as well as Imin have been calculated to be 4.6%, 14.4 Kw/cm2, 0.66 Kw/cm2, respectively. The Stark-level components of the 2F7/2 and 2 F5/2 were also determined. End-pumping crystal ZnWO4:Yb31 with 975 nm laser diode, we investigated the laser output property. The highest output power at wavelength 1017 nm was obtained to be 0.5 W, corresponding to the pumping power of 10 W and the threshold was about 2 W. PACS: 71.20.Eh; 78.20.-e; 65.60. 1a, 42.55.Xi, 42.55.Ye, 42.60.Gd. I. INTRODUCTION
Trivalent ytterbium ion (Yb31) is a very attractive laser ion with some unique characteristics. The two-energy level structure of Yb31 (2F7/2 ground state and the 2F5/2 excited state) causes no up-conversion, no luminescence quenching and can easily be obtained with commercial diodes. The electronic configuration 4f13 causes a stronger electronphonon interaction to make the optical spectra of crystal show broad absorption and emission bands.1–4 As a rareearth ion with the simplest energy level structure, it has many important merits such as high efficiency in energy conversion, longer fluorescence lifetime, larger capacity for effective energy storage, no excited-state absorption, and so forth. Because of the strong peak of absorption at wavelength ;970 nm, it is capable of being effectively coupled with the pump wavelength of laser diode (LD) to generate the ;1-lm laser or ;500-nm blue-green laser, which were generally used in the fields of atmospheric studies, military applications, medical procedures, storage and so forth. Crystal ZnWO4 has the monoclinic structure with P2/c space group. Its lattice parameters are: a 5 0.469 nm, b 5 0.572 nm, c 5 0.493 nm, and b 5 90005’. ZnWO4 is known as a laser host and a promising material as scintillator, optical fiber and so forth. And so, in this work, we grew the good quality ZnWO4:Yb31 single crystal by Czochralski method and investigated the spectroscopic property and the laser output.
ð1 xÞZnO þ WO3 þ 0:25xYb2 O3 þ 0:25xK2 CO3 ¼ CO2 [ þ K0:5x Yb0:5x Zn1x WO4
:
ð1Þ
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.126
Here, the doped concentration x is 4 at.%. The initial compounds were mixed in carnelian bowl and sintered for almost 3 days at 1020 °C. Then the charge was deposited in a Pt crucible bowl of U55 mm 30 mm and placed in the DJL-400 furnace (Beijing OptoElectronics Technology Co. Ltd., Beijing, China). With the Pt-wire rotating at a rate of 12 rpm and the pulling rate of 1.2 mm/h, the crystal was grown. When the procedure was over, the crystal was drawn out and cooled down to room temperature at a rate of 10–30 °C/h. The x-ray powder diffraction investigations were carried out with CAD4 diffractometer (Rigaku Corporation, Matsubara, Japan) equipped with Cu Ka radiation (k 5 1.54056 Å). The data
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