Crystal growth and spectroscopic properties of uranium dioxide doped LiNbO3 with multiband absorption

Lithium niobate crystals have excellent photorefractive properties and possess a great development promising in holographic applications. Doping ions with variable valences is of great importance to adjust their photorefractive properties. A series of 1 in. uranium dioxide doped LN crystals with 11 cm in length had been grown successfully by the modified vertical Bridgman method. The results showed that the crystals had high crystalline quality which was due to the average FWHM values of X-ray rocking curve was as narrow as 10 '', and the doped uranium ions were with three different valence states of +4, +5, and +6. Comparing with pure congruent LN crystal, the absorption edge of UO2 doped LN significantly red shifted about 184-218 nm as the concentration enhanced. A strong wide absorption in the region of 300-600 nm and an absorption peak centered at 740 nm were observed in uranium dioxide doped LN crystals. It indicated that charge carriers can be excited from different energy levels at various wavelengths, which may be beneficial to realize the multi-wavelength holography in uranium dioxide doped LN crystals.