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It has been demonstrated that by using doping and co-doping strategies the lifetimes as well as luminescence intensities of the doping species in the lanthanide oxysulfide nanoparticles (NPs) Ln 2 O 2 S:Ln’ 3+ (Ln=Gd, Tb, Eu; Ln׳=Tb, Eu, 1% and 5%) could be tuned. The lanthanide oxysulfide NPs, i.e., Gd 2 O 2 S, Tb 2 O 2 S and Gd 2 O 2 S:Tb 3+ (5%) were synthesized as matrices and doped with Eu 3+ (1% or 5%), by the thermal decomposition method and characterized by TEM, XRD, photoluminescence, cellular and in vivo animal imaging studies for potential luminescence bioimaging applications. Of these materials, Gd 2 O 2 S:Eu 3+ (5%) NPs possess the highest photo-stability and strongest luminescent intensity at 625 nm with a lifetime 853 μs in hexane. Surface modification of the Gd 2 O 2 S:Eu 3+ (5%) NPs with mPEG-APTES to increase its aqueous solubility resulted in almost complete luminescence quenching. Calcination of the host Gd 2 O 2 S:Eu 3+ (5%) NPs at 400 °C to increase their crystallinity and maintained some of their luminescence properties in aqueous solution. Further surface modification of the Gd 2 O 2 S:Eu 3+ (5%)-APTES NPs with mPEG and Alexa Fluor 660 allowed their effective cellular and in vivo animal luminescence imaging with low bio-toxicity. These novel imaging materials with tunable lifetimes would be potentially useful for luminescence bioimaging applications, particularly in the time-resolved, up-conversion, and/or multiplex modes. [ABSTRACT FROM AUTHOR]