Doping Triple Lanthanum Ions in GdPO4 Nanocrystals Through Multiple Synthesis Routes and Their Dual Mode Spectrum Conversion Behaviour

Doping multiple lanthanum ions in crystal of nanometer dimensions to achieve desired properties is an arduous task. This has been achieved in an important lanthanum phosphate (GdPO4) via three different synthesis routes including soft chemical processes such as room temperature co precipitation and pechini type sol-gel method and a facile solid state diffusion reaction. All the methods produce well crystalline nanoparticles with dimensions ranging from few nm to tens of nm but with different morphology. The three lanthanum ions Ho3+, Yb3+, Eu3+ introduce up and down conversion luminescence in GdPO4 nanocrystals making them simultaneously excitable by UV and IR light and emit in the visible. The concept of dual excitation nanophosphor is quite unique for applications such as security ink and solar spectrum conversion for efficient energy harvesting. Intense orange red emission from Eu3+ (D-5(0) - F-7(J) transitions) under broad UV excitation range (250 nm-400 nm) and predominant red emission from Ho3+ (640-654 nm, F-5(5)-I-5(8)) through two to three photon UC process under IR (980 nm) excitation in GdPO4:Ho3+, Yb3+, Eu3+ suggest a general approach to constructing a new class of luminescent materials with simultaneous up and down conversion emissions by controlled manipulation of energy transfer within a nanoscopic region