Increased Concentration of Yb3+ and High Crystal Field Strength in RbTiOPO4:Ta Single Crystal with Optimized Growth
Yb-doped inorganic crystals have attracted great attention in both basic and applied research, and the quest for suitable crystal hosts and understanding the corresponding crystal field environments are still worth studying in laser application. In this context, inclusion-free RbTiOPO4:Ta:Yb (RTP:Ta:Yb) single crystals with dimensions up to 3 × 30 × 15 mm3 were grown by top-seeded solution growth method under optimized growth conditions. The good crystalline quality of the as-grown RTP:Ta:Yb crystals were confirmed by X-ray diffraction rocking curve. The chemical compositions of the crystals were determined through electron probe microanalysis (EPMA). The results showed that the Ta distribution coefficient is 0.90–1.28, and the Yb distribution coefficient is 0.13–0.37. Double doping of Ta5+ ions can effectively increase the concentration of Yb3+ ions in the RTP crystal, and the concentration of Yb3+ ion in RTP crystal can reach 1.26 × 1020 atom/cm3. The influence of Ta and Yb dopants on the electronic structures of RTP crystals was studied using high-resolution X-ray photoelectron spectroscopy (XPS), and the chemical strengths of Ti–O and P–O bonds are related to the binding energy difference. RTP:Ta:Yb crystals exhibit excellent transparent performance in the wavelength range of 0.35–4.5 μm, and the transmittance is about 83%. Photoluminescence spectra show five emission peaks of Yb3+ in crystals, and the main emission peak is located at 972 nm. Two different coordination sites for Yb3+ were observed, and their energy levels were determined in the crystal field of the RTP:Ta structure. Furthermore, the crystal field strengths of Yb3+ in different host crystals associated with their distorted coordination environments were evaluated and discussed in detail. The results demonstrate that the RTP:Ta:Yb single crystal endowed with high crystal field strength and good luminescence property is suitable for laser application.
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