Ultraviolet upconversion luminescence of Gd³⁺ from Ho ³⁺ and Gd³⁺ codoped oxide ceramic induced by 532-nm CW laser excitation

Ultraviolet upconversion emissions around 314 nm from ⁶P _J states of Gd³⁺ ions have been observed in Y _{1.98 - x}Gd_xHo_0.02O₃ (x = 0.02, 0.10, 0.20, and 0.30) oxide ceramics under the excitation of a continuous-wave 532-nm laser. We found that the energy transfer process from Ho³⁺ to Gd³⁺ plays an important role in populating the ⁶P _J states of Gd³⁺. The doping of Gd³⁺ ions does not affect ⁵G₄ and ⁵G₅ states but only the ³D₃ state of Ho³⁺. The emissions from ³D₃ state decrease with the increase of Gd³⁺ concentration. Power dependence curves and time-resolved spectra have been measured to identify the proposed upconversion mechanism.