Down-conversion from Er 3+ -Yb 3+ codoped CaMoO 4 phosphor: A spectral conversion to improve solar cell efficiency

Abstract The present paper focuses on near infrared (NIR) down-conversion photoluminescence (PL) properties by studying the energy transfer mechanism between Er 3+ and Yb 3+ in CaMoO 4 :Er 3+ , Yb 3+ phosphors. We have successfully synthesized a series of Er 3+ doped and Yb 3+ codoped CaMoO 4 phosphors by hydrothermal method. The down-conversion of Er 3+ -Yb 3+ combination with CaMoO 4 phosphor is designed to overcome the energy losses due to spectral mismatch when a high energy photon is incident on the Si-solar cell. The XRD, FESEM, EDX, PL, UV–Vis, Lifetime measurements were carried out to characterize the prepared down-converting phosphors. The crystallinity and surface morphology were studied by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) techniques. The down-conversion PL spectra have been studied using 380 nm excitation wavelength. The Er 3+ doped phosphors exhibit hypersensitive emission at 555 nm in the visible region due to 4 S 3/2 → 4 I 15/2 transition. The addition of Yb 3+ into Er 3+ doped CaMoO 4 attribute an emission at 980 nm due to 2 F 5/2 → 2 F 7/2 transition. The decrease in emission intensity in visible region and increase in NIR region reveals the energy transfer from Er 3+ to Yb 3+ through cross relaxation. The UV–Vis–NIR spectra shows the strong absorption peak around 1000 nm due to Yb 3+ ion. The lifetime measurement also reveals the energy transfer from Er 3+ to Yb 3+ ions. The maximum value of energy transfer efficiency (ETE) and corresponding theoretical internal quantum efficiency are estimated as 74% and 174% respectively.