Investigation on up-conversion luminescence properties of novel transparent Ho3+-Tm3+-Yb3+co-doped oxyfluoride glass ceramics

Abstract

In the present letter, the transparent oxyfluoride glass ceramics containing Ho 3+ -Tm 3+ -Yb 3+ :NaYF 4 were successfully prepared by melt-quenching at 1400°C and subsequent heating at 650-680°C for 1~2 hours . X-ray diffraction (XRD) with Cu K α radiation (λ=0.154nm) investigation revealed that NaYF 4 nano-crystals in the glass ceramics was fabricated. Their sizes were determined by Sherrer's equation. The emission spectra red green and blue up-conversion (UC) under 980nm laser diode (LD) pumping and absorption spectra were measured. Luminescence measurements confirmed the partition of RE ions in nano-crystals NaYF 4 . The blue red and green UC radiations correspond to the transitions 1 G 4 - 3 H 6 , 1 G 4 - 3 H 4 of Tm 3+ , 5 F 4 , 5 S 2 - 5 I 8 , 5 F 5 - 5 I 8 , of Ho 3+ ions, respectively. This is similar to that in Tm 3+ -Yb 3+ and/or Ho 3+ -Yb 3+ co-doped glass ceramics. To obtain upconversion fluorescence mechanisms, upconversion fluorescence intensity versus LD pump power were analyzed in view of energy levels of rare earth. Up-conversion mechanisms were discussed and the ratio between red, green and blue UC emission bands was found to be varied as a function of temperature of heat treatment and pump power. This result could be mainly attributed to the cross-relaxation between Ho 3+ ions. The excellent optical properties and its convenient, low-cost synthesis of the present glass ceramic imply that it is an excellent substitution material for the unobtainable bulk NaYF 4 crystal and may have potentially applications in tunable visible laser or many other fields.