Sr(Ag_1-xLi_x)₂Se₂ and [Sr₃Se₂][(Ag_1-xLi_x)_{2Se2] Tunable Direct Band Gap Semiconductors}

Synthesizing solids in molten fluxes enables the rapid diffusion of soluble species at temperatures lower than in solid-state reactions, leading to crystal formation of kinetically stable compounds. In this study, we demonstrate the effectiveness of mixed hydroxide and halide fluxes in synthesizing complex Sr/Ag/Se in mixed LiOH/LiCl. We have accessed a series of two-dimensional Sr(Ag1-xLix)(2)Se-2 layered phases. With increased LiOH/LiCl ratio or reaction temperature, Li partially substituted Ag to form solid solutions of Sr(Ag1-xLix)(2)Se-2 with x up to 0.45. In addition, a new type of intergrowth compound [Sr3Se2][(Ag1-xLix)(2)Se-2] was synthesized upon further reaction of Sr(Ag1-xLix)(2)Se-2 with SrSe. Both Sr(Ag1-xLix)(2)Se-2 and [Sr3Se2][(Ag1-xLix)(2)Se-2] exhibit a direct band gap, which increases with increasing Li substitution (x). Therefore, the band gap of Sr(Ag1-xLix)(2)Se-2 can be precisely tuned via fine-tuning x that is controlled by only the flux ratio and temperature.