Efficient deep ultraviolet to near infrared quantum cutting in Pr³⁺/Yb³⁺ codoped CaGdAlO₄ phosphors

Pr³⁺/Yb³⁺ codoped CaGdAlO₄ (CGA) quantum cutting phosphors were synthesized by a self-propagating combustion method along with a subsequent heat treatment. For these phosphors, a deep ultraviolet (DUV) to near infrared (NIR) quantum cutting via the energy transfer from Pr³⁺ to Yb³⁺ ions has been realized under the 4f-5d excitation of Pr³⁺ when its 5d level is lower than the ¹S₀. It can be found that the cascade relaxation processes of the electrons from the excited 4f5d state to the ³P₀ state play a key role in obtaining the 4f-4f emissions of Pr³⁺. In addition, at the optimal Yb³⁺ concentration (6%), the most efficient DUV to NIR quantum cutting can be reached through the dominating two-step energy transfer from Pr³⁺ to Yb³⁺ upon DUV excitation ranging from 235 to 285 nm and the quantum cutting efficiency, η_QCE, of the phosphor is ∼166%. Strikingly, the temperature-dependent NIR emission spectra suggest that these quantum cutting phosphors, having a higher thermal activation energy of 320 meV, exhibit a good thermal stability. Meanwhile, it is found that the existence of the DUV to NIR quantum cutting gives the phosphor a high resistance to UV irradiation. Our results indicate that Pr³⁺/Yb³⁺ codoped CGA quantum cutting phosphors can be a candidate serving as a protective layer for silicon space solar cells.