\lambda\; n^{1/3}=(2 \pi^2)^{-1/6} h / (e\; m^{1/2})(n^{1/3} /\; z_{eff})^{1/2} =(2 \pi^2)^{-1/6}\; 2 \pi\; \hbar / (e\; m^{1/2})(n^{1/3} /\; z_{eff})^{1/2} = \\ =(2 \pi^2)^{-1/6} \;2\pi\; a_B^{1/2})(n^{1/3} /\; z_{eff})^{1/2}  = 2.78 \times 10^{-4} (n^{1/3} / z_{eff})^{1/2}