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Yb/Tm: YF 3 nanoparticles embedded transparent bulk glass ceramic was successfully prepared to explore its possible application in optical temperature sensors. Specifically, owing to the competition of electron population in the thermally coupled Tm 3+ 3 F 2,3 and 3 H 4 excited states, two upconversion emission bands corresponding to Tm 3+ : 3 F 2,3 → 3 H 6 transition and 1 G 4 → 3 F 4 one exhibited opposite temperature-dependent behaviors, which resulted in monotonous enhancement of the related fluorescence intensity ratio with increase of temperature. As a consequence, Tm 3+ activators in the present YF 3 glass ceramic had advantages of a high sensitivity of 1.84% per K, an avoidable spectral overlapping and a negligible thermal effect for accurate temperature detecting. [ABSTRACT FROM AUTHOR]

Lanthanide-activated cubic Na 5 Gd 9 F 32 nanocrystals were precipitated from a borosilicate glass with a specifically designed composition. The precursor glass is already phase-separated after melt-quenching, which is beneficial to the realization of the controllable glass crystallization for affording desirable size, morphology and activator partition. Elemental mapping in the scanning transmission electron microscopy evidenced that the segregation of lanthanide ions into the Na 5 Gd 9 F 32 lattice was in situ formed without the requirement of long-range ionic diffusion. Impressively, such fabricated glass ceramic co-doped with Yb 3+ /Er 3+ ions exhibited intense upconversion luminescence, which was about 500 times higher than that of the precursor glass, and its luminescent color could be easily tuned from red to green by controlling glass crystallization temperature. It is anticipated that such phase-separation synthesis strategy with precise control over nanostructure of glass ceramics offer a great opportunity to design other highly transparent nanocomposites with a wide range of tunable optical properties. [ABSTRACT FROM AUTHOR]