Nd:YLF Crystal Growth: Raw Materials Preparation by Melting Method and Property

doi:10.15541/jim20240456

Abstract

Abstract:

Nd³⁺-doped LiYF₄ (Nd:YLF) crystal is a laser crystal with excellent performance, which is widely used in scientific research, industrial and medical fields. But its existing crystal growth method using binary fluoride mixtures is problematic due to fluoride oxides being formed in fluoride raw materials, and process of preparing raw materials by using HF gas fluorination is relatively complicated. Therefore, preparation of high-purity fluoride raw materials is one of the important factors to realize the growth of high-quality fluoride crystals. Meanwhile, crystal growth atmosphere usually contains CF₄ or HF, which is highly corrosive to growth system and increases cost of crystal growth. In this work, to obtain high-quality Nd:YLF crystal, the polycrystalline growth raw material with high-purity YLF crystalline phase was first prepared using a nearly closed melting material device, which was a novel design facilitating the melting process and floating salvage process at the temperature above the crystal melting point. Intact Nd:YLF crystal was obtained after growth under a high-purity Ar atmosphere. X-ray diffraction (XRD) patterns of polycrystalline raw materials and growing crystals were tested, while lattice parameters, atomic coordinates, atomic occupancy and temperature factor were obtained by Rietveld refinement. By measuring X-ray rocking curve (XRC) of (100) crystallographic plane of the as-obtained Nd:YLF crystal, the full width at half maximum (FWHM) of diffraction peak is 0.007°. The segregation coefficient of Nd³⁺ in YLF calculated by measuring the content of each element is 0.3. The strongest absorption peaks of Nd:YLF crystal locate at 797.4 nm (a direction) and 792.3 nm (c direction) with absorption cross sections of 3.37×10^-20 and 5.49×10^-20 cm², respectively. The strongest emission peak of Nd:YLF crystal locates at 1047 nm with stimulated emission cross section of 1.598×10^-19 cm² and fluorescence lifetime of 483 μs. Based on above data, Nd:YLF polycrystalline raw materials prepared by melting method achieve high phase purity. Combined with Czochralski method of crystal growth with vacuum extraction and heating process, the present growth method can greatly reduce the formation of fluoride oxide during the growth process, which proves a successful growth under Ar atmosphere.

Key words: Nd:YLF, laser crystal, crystal structure, spectral analysis

CLC Number:

O734
O657

ZHAO Kaixuan, LIU Wenpeng, DING Shoujun, DOU Renqin, LUO Jianqiao, GAO Jinyun, SUN Guihua, REN Hao, ZHANG Qingli. Nd:YLF Crystal Growth: Raw Materials Preparation by Melting Method and Property[J]. Journal of Inorganic Materials, 2025, 40(5): 529-535.

Figures/Tables 12

Fig. 1 Schematic diagram of raw material melting device

Fig. 2 Polycrystalline material prepared by melting method

Fig. 3 Nd:YLF crystals grown by Czochralski method (a) Crystal grown with polycrystalline material prepared by melting method; (b) Crystal grown with mixed component raw materials

Fig. 4 XRD pattern of polycrystalline material prepared by melting method

Fig. 5 XRD pattern of whiteness among crystal grown with mixed component raw materials

Fig. 6 XRC of Nd:YLF crystal

Fig. 7 Rietveld fitting XRD patterns of Nd:YLF crystal

Table 1 Structural parameters of Nd:YLF crystal obtained by Rietveld refinement method

Element	X	Y	Z	Occupancy	Uiso
Li	0	0.25000	0.12500	0.25000	0.20666
Y	0.50000	0.75000	0.12500	0.24750	0
Nd	0.50000	0.75000	0.12500	0.00250	0
F	0.27376	0.09431	0.04622	1.00000	0
Lattice parameter		a=b=0.51696 nm, c=1.07412 nm, α=β=γ=90°
R factor		R_p=6.39%, R_wp=8.31%

Table 2 Element contents of Nd:YLF crystal tested by LA-ICP-MS method

Sample	Mass fraction/%
Sample	Nd	Y	Li
Sample 1	1.7659	88.8208	7.3685
Sample 2	1.7726	89.8067	7.5738
Sample 3	1.7939	88.4968	7.9348
Average	1.7775	89.0414	7.6257

Fig. 8 Transmission spectra of Nd:YLF crystal at room temperature

Fig. 9 Emission spectrum of Nd:YLF crystal excited by 808 nm

Fig. 10 Fluorescent decay curve of Nd:YLF crystal at 1047 nm

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