[Stokes and anti-stokes luminescence research of NaYF4:Eu3+, Tm3+, Yb3+].

The sample of NaYF4:Eu,Tm,Yb was synthesized by coprecipitation method. The emission of NaYF4:Eu,Tm,Yb excited by 360 nm is blue light with the peak at 452 nm from the transition of (1)D2-->(3)F4 of Tm3+. After being excited by 395 nm, NaYF4:Eu,Tm,Yb emits orange light with the peak at 591 nm originating from the transition of (5)D0-->(7)F1 of Eu3+. When excited by 409 nm, NaYF4:Eu,Tm,Yb emits red light with the peak at 613 nm from the transition of (5)D0-->(7)F2 of Eu3+. The color of upconversion luminescence of NaYF4:Eu,Tm,Yb excited by 980 nm was blue and red. The upconversion spectrum exhibits distinct emission peaks at 459, 478 and 641 nm. The blue light comes from the transition of (1)G4--(3)H6 and (1)D2-->(3)F4 of Tm3+. The absorption spectrum was also researched. The red light results from the transition of (1)G4--(3)F4 of Tm3+. The slope of the emission of 474 and 646 nm is 2.1 and 2.4 respectively. The emission of 478 and 641 nm is all due to three photon process. The structural properties of sample were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that NaYF4:Tm3+,Yb3+ prepared by coprecipitation method exhibits a hexagonal crystal.