Upconversion luminescence of Yb3+: Tm3+ and Yb3+: Tm3+: Er3+- doped Beta-Tricalcium Phosphate nanoparticles

Abstract

A novel class of fluorescence nanoparticles of 5.5 mol% of Yb3+, 0.5 mol% of Er3+ and 0.5 mol% Tm3+: calcium deficient hydroxyapatite were synthesized by co-precipitation method in aqueous solution (pH adjusted to 6) and specially treated with microwave radiation at 1000°C for 10 minutes to produce nanocrystals of Yb:Tm: and Yb:Tm:Er:-tricalcium phosphate (-TCP). As a result, we report for the first time, a single-phase -TCP:Yb:Tm:Er and -TCP:Yb:Tm exhibiting an efficient visible and near infrared upconversion luminescence from the 1G4 (blue emission), 4S3/2 (green emission), 3F2 (red emission) and 3H4 (near infrared emission) induced by the Yb3+ Tm3+ / Er3+ energy transfer under pulsed laser excitation at 972 nm (Yb3+) with an average energy of 11 mJ. The emission decay curves of the upconversion transients, from 1G4 excited state of Tm3+ and 4S3/2 excited level of Er3+, indicate that ESA process occurs in -TCP:Yb/Tm/Er nanopowder measured for the 550 nm luminescence of Er3+, which has a time constant (t2) of 0.4 s. However, Yb3+  Tm3+ upconversion (Up2) has a time constant (t2) of 14.4 s and does not exhibit ESA absorption. This -TCP activated by Yb3+ and Tm3+ ions constitutes a new nanobiomaterial that can be used as diagnostic and therapeutic agents, affording deeper tissue penetration and higher resolution and sensitivity for visible-near infrared bioimaging and treatments.