Getting a Handle on Upconverting Nanoparticles

I wrote about upconverting nanoparticles way back in July of 2009. These nanoparticles absorb energy in near-infrared region and emits higher energy visible light, hence the name ‘Upconverting’. Though attractive, their wider adaptation in biosensing or as luminescent biological labels has been hampered because of difficulty in controlling their size and optical properties. The recent article in Nature however intends to solve these problems by providing a new method to control the size and optical emission properties of Upconverting nanoparticles.

Advantages of Upconverting Nanoparticles

  • High photochemical stability
  • Sharp emission bandwidth
  • Large anti-Stokes shift of upto 500nm
  • Absence of autofluorescence from biological materials because on near infrared excitation and
  • Combined with excellent light penetration depth they are ideal for imaging

Problems of Upconverting Nanoparticles

  • Not easy to prepare small (sub 20nm) sized particles. As the size is reduced, the nanoparticles undergo phase change from anisotropic (hexagonal) to isotropic (cubic) resulting in decrease in upconversion luminescence
  • Difficult to control optical properties
  • Difficult to synthesize-need high temperature (~300 °C), prolonged temperature (up to several days), hazardous reaction conditions

Solution: Lanthanide doping resulting in

  • lower temperature (~230 °C),
  • reduced reaction time (2h),
  • small particles (10nm)
  • Strong upconverting efficiency and
  • Control over emission colors

I have a feeling we will be hearing a lot about these wonderful particles!

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