Investigation of Er3+‐Doped BaF2 Single Crystals for Infrared Emission and Photovoltaic Efficiency Enhancement

ABSTRACT Er 3+ ‐doped BaF 2 single crystals were investigated with two primary aims: first, to probe the infrared emissions from the 4 I 11/2 level (around 1.0 μm) under 1500‐nm excitation and, second, to use the crystal to enhance the efficiency of silicon‐based solar cells through upconversion mechanism. Upon excitation at 1500 nm, the upconversion emission spectrum of the Er 3+ ‐doped BaF 2 single crystals, recorded in the range of 480–1080 nm, exhibited two well‐structured visible bands at 538 and 650 nm, along with a strong near infrared emission at 971 nm. This strong 971‐nm emission has an emission cross‐section of approximately 0.23 × 10 −20 cm 2 . As with any phenomenon inherent to energy transfer by upconversion, the 4 I 11/2 fluorescence decay exhibits a rise time followed by a long decay of approximately 15 ms and a positive optical gain from the low values of the population inversion coefficient, which could potentially give rise to laser emission from this level. When we place our crystal on a photovoltaic device illuminated by 1500‐nm wavelength radiation, we record a photocurrent of 300 μA at an illumination power of 85 mW. This indicates that the Er 3+ ‐doped BaF 2 crystal is highly suitable for significantly enhancing the efficiency of silicon‐based solar cells.