Size effect in luminescent properties of LiNdP4O12 nanocrystals

• The 4F3/2  → 4I11/2 to 4F3/2  →  4I9/2 intensities ratio increases with the grain size.
• The luminescence decay time of 4F3/2 state becomes longer with increase of the grain size.
• Observed size effect was discussed in terms of size dependence of energy diffusion.

The LiNdP4O12 nanocrystals were synthesized using co-precipitation method. The grain size of the nanocrystals was controlled by heat treatment. The average grain size was determined from XRD analysis and confirmed by TEM images to be in range 42–240 nm. Impact of the average grain size on the luminescent properties of LiNdP4O12 nanocrystals was investigated. With increasing grain size the luminescence ratio 4F3/2 → 4I9/2 to 4F3/2 → 4I11/2 decreases due to the reabsorption of resonant luminescence 4F3/2 → 4I9/2 transition. A significant enhancement of decay rate of 4F3/2 was observed. Both of the effects are discussed in terms of enhancement of diffusion rate with increasing the size of nanocrystals.

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