Single crystal structure and optical properties of nonlinear optical crystal Rb0.94Ti0.94Ta0.06OPO4

Abstract

Rb_0.94Ti_0.94Ta_0.06OPO₄ (RTP:Ta) single crystal was grown by the top seeded solution growth method. The good crystalline quality of the as-grown crystal was confirmed by the X-ray rocking curve analysis. The chemical composition was analyzed by performing electron probe microanalysis (EPMA) and inductively coupled plasma optical emission spectrometry (ICP-OES). Detailed structural investigations were performed through the Single-Crystal X-ray diffraction technique. The cell parameters of Rb_0.94Ti_0.94Ta_0.06OPO₄ are a = 12.9604(2) Å, b = 6.4988(9) Å, c = 10.5705(2) Å and V = 890.3(2) ų. It is shown that Ta⁵⁺ ions replace Ti⁴⁺ ions in the structure, and the electroneutrality of the crystal is stabilized by creating Rb⁺ vacancies. Ta cations occupy both Ti(1) and Ti(2) sites; the occupancies of Ta cations in Ti(1) sites and Ti(2) sites are 0.077(4) and 0.048(4), respectively. The Rb vacancy rate is 0.062(1) and more Rb vacancies are found at Rb(2) sites. It is shown that the occupancies of Ta and Rb cations correlate with the bond lengths of Ti–Rb and Rb–O. Rb_0.94Ti_0.94Ta_0.06OPO₄ single crystal exhibits high transmittance up to 85% in the range of 0.35 to 4.5 μm. The UV cutoff wavelength of Rb_0.94Ti_0.94Ta_0.06OPO₄ shows a 6 nm red-shift compared to that of RTP. At the wavelength of 1064 nm, the absorption coefficients for Rb_0.94Ti_0.94Ta_0.06OPO₄ crystal along a, b and c-directions are 0.19 cm⁻¹, 0.15 cm⁻¹ and 0.06 cm⁻¹, respectively. The second harmonic generation (SHG) efficiency of Rb_0.94Ti_0.94Ta_0.06OPO₄ is about 1.4 times that of RTP. The relationship between the crystal structure and the nonlinear optical property of Rb_0.94Ti_0.94Ta_0.06OPO₄ is discussed in detail. The distorted TiO₆ octahedra and typical short Ti–O bonds endow this crystal with SHG efficiency comparable to that of RTP. Our results indicate that Rb_0.94Ti_0.94Ta_0.06OPO₄ crystal is an excellent nonlinear optical material for potential applications.