Dual-color upconversion photoluminescence induced by disordered Yb3+-Ti4+ pairs and defects in highly stable langbeinite-type Rb2Ti0.80Yb1.20(PO4)3 single crystal

Inorganic upconversion materials show significant importance in both basic research and applied area, and searching for suitable host material and understanding of fundamental photophysical process are particularly worth studying in upconversion application. Herein, a heavily Yb 3+ -substituted langbeinite-type Rb 2 Ti 0.80 Yb 1.20 (PO 4 ) 3 (RTYP) millimeter-sized single crystal, which has been successfully grown by high temperature solution method, exhibits efficient dual-color upconversion photoluminescence under 980 nm excitation. The lifetimes of two-photon blue emission and one-photon red emission are 4.1 μs and 17.1 μs, respectively. X-ray structural analyses reveal that the dual-color emissions are ascribed to disordered Yb 3+ -Ti 4+ pairs and crystal defect, and the higher intensity of red emission is attributed to Yb 3+ -defect energy transfer activated by Ti 4+ . Notably, the blue emission originates from cooperative luminescence of Yb 3+ dimer, and the red emission originates dominantly from the cooperative sensitization of the intrinsic defect caused by excited Yb 3+ dimer. Moreover, RTYP with disordered structure shows high thermal stability up to 1,150 °C. This work not only demonstrates the promising potential of langbeinite-type materials in multicolor upconversion application, but also sheds light on the photophysical process associated with disordered crystal structure.