Materials Research Bulletin, Vol. 30, No. 1, PP. 19-26, 1995 Copyright 0 1994 Elsevier Science Ltd Printed in the USA. All rights reserved 0025-5408/95 $9.50 + .OO
OF NEODYMIUM CRYSTALS
T. Katsumata, K. Hanamori, Y. Akiyama and Y. Nobe* of Applied Chemistry, Faculty of Engineering, TOY0 University; 2100 Kujirai Nakanodai, Kawagoe, Saitama 350, Japan lR and D Center, Mitsui Mining and Smelting Co. Ltd.; 1333-2 Haraichi, Ageo, Saitama 362, Japan
ABSTRACT The melting temperatures, the lattice parameters and the optical properties of Nd doped Bi12Si020 have been studied for the diode pumped laser applications. The lattice parameters and the melting temperatures decrease from 10.1055 to 10.1035 A and from 900 to 890 “C with Nd2Q concentration from 0 to 5 mol%. The crystals grown by Czochralski technique are transparent up to A=500 nm. The width of the optical absorption peak due to Nd3+ ion (h=815 nm) is broader than that of Nd doped Y3A 15012. Segregation coefficient of Nd The solubility limit of Nd2Q into is estimated to be about k=0.17. Bi12Si020 is also suggested to be about 5 mol%. MATERIAL INDEX: Bismuth, Neodymiun, Silicon, Oxide
Introduction non-linear and/or optics oxide electro-optics single Recently, ions such as Nd doped LiNb03 crystals doped with laser active lanthanide (Nd:LN) and Nd doped LiTa (Nd:LT) have been expected as a self-doubling and/or a self-modulating solid-state laser crystal [l-7]. Diode-laser (LD) pumping technique enables the colored crystal, such as Bi4GeaQ2 (BGO), to be used as a laser host , because the wavelength of the exciting beam is usually h=808 nm for pumping Nd3+ ions. narrow, Bi, 2SiO2o extremely (BSO) crystal is expected to be a laser host because ionic radius of BP+ (r=1.20 A) is similar to that of Nd3+ (r=1.15 A). Moreover, BSO has 19
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magneto-optic, electro-optrc, piezoelectrrc, photo conductive refractive characteristics for the laser light control. BSO single has been used widely for an optical-fiber voltage and current crystal sensor, an optical spatial light modulator and/or a surface acoustic device However, little have been reported on the phase relation, (SAW) [g-13]. crystal growth and the optical propertres of Nd doped BSO crystal. favorable and photo
In this paper, the lattrce parameters and the melting temperatures of the sintered specimens were measured to investigate the phase relation in Nd&- B i , 2Si020 pseudo-binary system. The optical properties of Nd doped using also evaluated Czochralski grown single Bi1$Si020 (Nd:BSO) were A phase relation and the optical properties of Nd doped Bi12SiOZ0 crystals. crystals are described in detail
Experimental In order temperatures of
Nd doped Br12Si020, specimens were prepared by a solidphase reactron from (4N) 8124. (6N) 902 and (3N) Nd2C& powders. Powders were mixed in an adequate proportion, then sintered at 800 “C for 18 h and for 6 h at 850 “C in Pt crucible They were then cooled quickly to room The specimens were prepared with various Nd concentrations temperature. oriented single crystals were grown using a from 0 to 15 mol%. resistance heating Czochralskr technique [14-l 51. Seed rotating rate was Crystals were grown from 50 cm3 10 rpm, pulling rate was 2 mm/h Grown crystals were cut along (110) and (111) plane. volume Pt crucible. Each slice was mirror polished at both surfaces. The lattice parameters were measured on all the specimens using a Rigaku RINT-I 100 type diffractmeter with Cu ktx radiation through a Ni Silicon powder was used as a standard for determining the lattice filter. Melting temperature were measured by a differential thermal parameters. analysis (DTA) (Rigaku Thermoflex TG-81 IO) with the heating rate of 20 Melting specimen. 150 mg powder temperature “C/min using was measured from an endothermrc peak in the DTA curve. Optical absorption measured crystals was using Shimadze UV-3100 type single of the The photoluminescence spectrum was measured using spectrophotometer of Jobin Ybon Type-320 monochrometer, a Si a system which consisted photo detector and a laser diode (Sharp LTOlGMDO) with peak power of 40
intensities with the wavelength photoluminescence was evaluated by controlling the temperature of the
of the exiting laser diode from
The wavelength of the exiting beam increases linearly 40 “C. to 813 nm with the diode temperature from 10 to 40 “C.
the beam 0 to
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BISMUTH SILICATE CRYSTALS
Variation in the aaxis lattice parameters and the melting temperatures of Nd doped Bi12Si020.
Results and discussh The and
the specimens are shown in Fig. 1. The melting temperature gradually decreases from 900 to 890°C with Nd concentration from 0 to 15 mol%. The a-axis parameter 10.1055
from 0 to 15 mol%.
solubility Bi,,SO,, less
Nd limit is 5
grown crystal. Crystals and transparent.
a typical are brown
Al Ca 1 5 -__.--____
Mg Mn ,.-_----_
concentrations of grown crystals coupled plasma (ICP)
of grown crystal measured by the induction
coupled plasma (ICP)
is shown in Table 1. Highly pure single crystals are successfully
by Czochralski technique.
Nd into Bi,,SiO,O The optical
crystal is suggested
for (110) slice
3. Absorption crystal
to be less than unity, k=0.17.
A=500 nm. Absorption bands due to Nd3’ ion are clearly spectrum.
A=815 nm usually used for the pumping of the laser is not disturbed by the fundamental absorption of the host crystal. In Fig. 4, absorption
single crystals were shown in Fig.
mol% Nd,O, doped Bi,,SiO,,
of the crystal grown from the melt
with 5 mol% Nd20s is 0.87 mol%. From this result, segregation
the optical absorption
700 800 Wavelength.h,
900 ( nm 1
A=81 5 nm of a (110) slice of 5 mol% Nd,O, doped Bi,,SiO,, is shown as compared with that of Nd doped Y,AI,O,, crystal. The full width at the half maximum (WHM) of the absorption peak at A=815 nm of Nd:BSO (PWHM=2.8 nm
Optical absorption spectrum of the (110) slice of 5 mob% NdpQ doped Bi12Si020-
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BISMUTH SILICATE CRYSTALS
is wider than that of Nd doped Y&5O,2 (RNHM=l.i nm) at A=808 nm. It may imply . . that Nd doped BI,,SIO, is suitable as the diode pumped laser crystal, because the wider absorption band can cover the variation in the lasing wavelength with temperature. Bi,,SiO, crystal is a solid-solution itself [la]. The broad absorption band may be due to the nonstoichiometric ‘nature of Bi,,SiO,O crystal.
Figure 5 shows the photoluminescence from (110) and (111) slices of 5 mol% Nd,O, doped Bi,,SiO,, single crystal exited by diode-laser (LD) operated at A=812 nm. The Bi,,SiO,, crystal is transparent around the peak wavelength of the photoluminescence. Photoluminescence peaks are observed at A=1071, 1085, 1098, 1105 and
concentration from 0 to 5 mol%. It then decreases with Nd
concentration. Photoluminescence intensity (110)
760 770 780 790 800 Wavelength, X. ( nm )
Fig. 4 bands absorption Optical around A=808 nm of the (110) slice of 5 mol% NdnQ doped with Bi1$3i020 as compared Of Nd doped Y&l&12 that crystal. single
( A =812nm)
Full width at the half maximum (FWHM) of the main peak at A=1071 nm is 8.3 nm. Intensity of photoluminescence at A=1071 nm increases with Nd
1080 1100 1120 Wavelength (nm)
Fig. 5 spectrum Photoluminescence from the (110) and the (111) slices of 5 mol% Nd& doped Bi12Si020, Photo-luminescence using spectrum was measured laser diode operated at various temperatures from 0 to 40 “C as an exiting beam.
than that from (111) slice. the in variations The photoluminescence intensity (A=1071 nm) with the temperature of exiting laser diode are shown in Fig. 6. The wavelength of the laser beam varies from 606 to 613 nm with the temperature of the laser diode from 0 to 40°C. In Fig. 6, the intensity of the photoluminescence from (110) and (111) slices of 5 mol% Nd,O, doped Bi,,SiO,, crystal is plotted against the temperatures of the laser diode. The intensity of the photoluminescence (A=1071 nm) from the (111) slice is greater than that from the (110) slice. The photoluminescence intensity of the (111) slice increases more dramatically with the temperature of the laser diode.
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of laser diode
Fig. 6 Photoof Peak intensity luminescence from the (110) and the (111) slices of 5 mol% Nd2Q doped Bil2SiO20 exited by the laser diode operated at The various temperatures. laser peak wavelength of the diode increases from 807 to temperature 813 nm with the from 6 to 40 “C.
The concentration of Nd in Bi,,SiO, single crystal is rather low; it is about 0.67 mol%. The segregation coefficient of Nd into Bi,,SiO, single crystal is suggested to be about k=0.17. From the ionic radius of Bi”+, Si4+ and Nd3’, and the variation in the lattice parameters, it is probable that Bi substitute Nd in the crystal. Nd doped Bi,,SIQ, single crystal is an attractive crystal because of it valuable electro-optical nature. However, there are many problems of the Nd concentration and/or photo refractive to be solved for the future laser application. The broad absorption band seen in Nd doped Bi,$iO,, crystal is suggested to be due to the compositional variation in the crystal that are similar to those in Nd doped WO, and Nd doped LiNbO, crystals [17, 181.
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BIShfUTH SILICATE CRYSTALS
Conclusion Effects of Nd doping into Bil2SiO20 single crystals have been studied for the diode pumped laser applications. Nd doped Bil2SiO20 single crystals are found to have some favorable optical properties for the laser applications. BSO crystals are transparent from infrared to A=500 nm. Optical pumping by the laser diode is, therefore, not disturbed by the fundamental absorption of the host crystal. Nd:BSO crystals are thought to be pumped more effectively, because the absorption bands of Nds+ ion at around h=800 nm is broader than those of Nd doped Y3Al&2. The solubility limit of Nd2Q is estimated to be about 5 mol% from the melting temperature and the lattice parameters. This value is considered to be enough for the laser applications, although the segregation coefficient of Nd is small. k=0.17.
Acknowledaments The authors university, for his Inorganic Materials experiments.
would like to encouragement. Laboratory, Toyo
thank Professor H. Imagawa, Toyo They also thank members of the University, for the assistance in the
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