Ultraviolet and violet upconversion luminescence in Ho3+-doped Y2O3 ceramic induced by 532-nm CW laser

Ultraviolet and violet upconversion luminescence spectra of holmium-doped Y2O3 were produced under the excitation of a compact continues-wave 532 nm solid-state laser. Emissions around 306, 362, 412, 390 and 428 nm can be assigned to the transitions of 3D3 → 5IJ (J = 8, 7, 6), 5G4 → 5I8 and 5G5 → 5I8, respectively. Power dependence and upconversion dynamics analysis demonstrated that both the energy transfer upconversion (ETU) and the excited state absorption (ESA) processes were involved in the population of 3D3 state via the coupled intermediate states 5S2/5F4. Fluorescence spectra in the visible and infrared ranges showed that 5G4 and 5G5 states were populated by the ESA process from 5I6 and 5I7 states, respectively, while the 5I6 and 5I7 states were radiatively populated from the excited 5S2/5F4 states. Upconversion mechanisms have been evaluated based on a rate equation model.

Research highlights▶ Using a continuous wave solid state green laser to induce ultraviolet upconversion emissions in Ho3+-doped Y2O3 ceramic. ▶ With the help of an electro-optic modulator which is modulated by square wave signals, the time-resolved fluorescence spectra were measured under the CW laser excitation. The measured decay curve contains information about the level population evolution process which is origin from the steady state, i.e., the energy transfer process was involved in the result. Thus, such measurement is different from traditional method of employing pulse laser as pumping source. ▶ A rate equation model was employed and well explained the experimental results.