Upconversion luminescence of Tm3+- and Yb3+-codoped pentaphosphate noncrystalline under the pumping of a 798-nm laser diode

When excited into Tm3 3F4 level by a LD at approximately 798 nm, Tm3 and Yb3 codoped pentaphosphate noncrystalline samples emit blue light at 475 nm, which corresponds to transition 1G4 yields 3H6. Although laser is directly absorbed by Tm3+ ions, the upconversion process rely on the codoping of Yb3+ ions. One Tm3+ yields Yb3+ transfer process excites Yb3+ ions, then backward Yb3 yields Tm3 energy transfer excites Tm3 ions from 3H4 to 1G4 level.