Rare Earth Ion Doped Oxyfluoride Glass Ceramics Upconversion Photoluminescence Study

The trivalent ions of rare earth have abundant energy evels. Rare-earth ion doped upconversion luminescent materials exhibit a wide range of potential applications in environmental-friendly lighting, fluorescent labels for biomolecules, shortwave laser, information display and photoelectron, etc. Nowadays the rare-earth doped glass ceramics become a hotspot. In this paper, we study the spectrum properties and the upconversion luminescent mechanism of NaYF₄ glasse ceramics doping Er³⁺/Yb³⁺, Tm³⁺/Yb³⁺ and Tm³⁺/Er³⁺/Yb³⁺.A series of samples of Er³⁺/Yb³⁺ co-doped, Tm³⁺/Yb³⁺ co-doped and Tm³⁺/ Er³⁺/Yb³⁺ co-doped NaYF₄ galss ceramics with different concentration were prepared by high-temperature melting, respectively. The formation of NaYF₄ nanocrystals was confirmed by X-ray diffraction in the glass ceramics.Upconversion fluorescence emission spectra of the samples of Er³⁺/Yb³⁺ co-doped, Tm³⁺/Yb³⁺ co-doped and Tm³⁺/ Er³⁺/Yb³⁺ co-doped NaYF₄ galss ceramics under 976 nm excitation were measured. 668 nm red (4I9/2â†'4I15/2) , 520 nm green (2H11/2â†'4I15/2) and 550 nm green (4S3/2â†'4I15/2) emissions were observed in the samples of Er³⁺/Yb³⁺ co-doped. 475 nm blue (1G4â†'3H6), 651 nm red (1G4â†'3H4) and 790 nm near infrared (3H6â†'3H4) emissions were observed in the samples of Tm³⁺/Yb³⁺ co-doped. Intense blue (476 nm), green (520 and 550 nm) and red (651 and 668 nm) emissions were simultaneously observed in the samples of Tm³⁺/ Er³⁺/Yb³⁺ co-doped. Red, green and blue light integral intensity changes with the diversification of doped concentration. Luminous mechanism has been explored according to the energy level matching and level scheme of Er³⁺, Tm³⁺ and Yb³⁺ on the basis of spectra and power dependence. The emissions of 475 nm and 651 were mainly three-photon process. The emissions of 520 nm, 550 nm, 668 nm and 790 nm were mainly two-photon process.According to the absorption spectra, the J-O intensity parameters ?λof Er³⁺ and Tm³⁺ were calculated based on Judd-Ofelt theory. The value of luminous intensity depends on the value of ?λ. The diversification of Er³⁺ and Tm³⁺ luminous intensity by calculation was consistent with experimental results in the samples.