Energy band gap \\\\(E=2.8\\ eV\\\\)\\\\(E=\\dfrac{hc}{\\lambda}\\\\)\\\\(\\Rightarrow\\dfrac{6.6\ imes10^{-34}\ imes3\ imes10^8}{6000\ imes10^{-9}\ imes1.6\ imes10^{-19}}=0.207\\ eV\\\\)The energy of a signal of wavelength \\\\(6000\\ nm\\\\) is \\\\(0.207\\ eV\\\\), which is less than \\\\(2.8\\ eV\\\\), the energy band gap of a photodiode. Hence, the photodiode cannot detect the signal.