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In the present letter, the transparent oxyfluoride glass ceramics containing Ho3+-Tm3+-Yb3+:NaYF4 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 Kα radiation (λ=0.154nm) investigation revealed that NaYF4
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 NaYF4. The blue red and green UC radiations
correspond to the transitions 1G4-3H6, 1G4-3H4 of Tm3+, 5F4,
5S2-5I8, 5F5-5I8, of Ho3+ ions, respectively. This is
similar to that in Tm3+-Yb3+ and/or Ho3+-Yb3+ 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 Ho3+ 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 NaYF4 crystal and may
have potentially applications in tunable visible laser or many other fields.
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