We report on an experiment that demonstrates the frequency up-conversion of telecommunication wavelength single-photon-level pulses to be resonant with a $mathrm{Pr}^{3+}$:$mathrm{Y}_2mathrm{Si}mathrm{O}_5$ crystal. We convert the telecom photons at
$1570,mathrm{nm}$ to $606,mathrm{nm}$ using a periodically-poled potassium titanyl phosphate nonlinear waveguide. The maximum device efficiency (which includes all optical loss) is inferred to be $eta_{mathrm{dev}}^{mathrm{max}} = 22 pm 1,%$ (internal efficiency $eta_{mathrm{int}} = 75pm8,%$) with a signal to noise ratio exceeding 1 for single-photon-level pulses with durations of up to 560$,$ns. The converted light is then stored in the crystal using the atomic frequency comb scheme with storage and retrieval efficiencies exceeding $eta_{mathrm{AFC}} = 20,%$ for predetermined storage times of up to $5,mumathrm{s}$. The retrieved light is time delayed from the noisy conversion process allowing us to measure a signal to noise ratio exceeding 100 with telecom single-photon-level inputs. These results represent the first demonstration of single-photon-level optical storage interfaced with frequency up-conversion.
