Optical And Luminescence Properties Of Rare-earth Ions In Bismuth Tellurite Glasses

Glasses doped with various rare-earth ions are important materials for fluorescent display devices, optical detectors, bulk lasers, optical fibers, waveguide lasers and optical amplifiers. Of the oxide glasses, tellurite glasses catch much attention in recent years because their maximum phonon energy is lower than those in silicate, borate, phosphate and germanate glasses. Rare-earth ions can be expected that the non-radiative loss to the lattice will be small and the fluorescence quantum efficiency will be high in tellurite glasses.In this work, alkali-barium-bismuth-tellurite (LKBBT) glasses were designed based upon traditional tellurite glasses. Optical and luminescence properties of rare-earth ions in bismuth tellurite glasses have been studied at room temperature. The results and progresses obtained are as follows.1. Pr³⁺—doped bismuth tellurite glass with molar composition 7.5Li₂O-7.5K₂O-5BaO-5Bi₂O₃-75TeO₂(LKBBT—Ⅰ) glass has been fabricated and characterized. The glass emits red lights under the excitation of long-wave UV and blue lights. The emission spectrum of Pr³⁺-doped bismuth tellurite glass under 488nm excitation consists of six intense emission bands peaking at 530nm, 616nm, 647nm, 684nm, 708nm and 732nm, owing to the ³P₀→³H₅, ¹D₂→³H₄, ³P₀→³F₂, ¹D₂→³H₅, ³P₀→³F₃ and ³P₀→³F₄ transitions, respectively. The excitation spectrum for 647nm emission of Pr³⁺ consists of three bands peaking at 448nm, 473nm and 486nm, respectively.2. Tm³⁺/Yb³⁺—codoped LKBBT—Ⅰglasses have been synthesized. The absorption spectra, fluorescence spectra and IR transmittance spectra of this glass were measured and analyzed. Based on J-O theory, and intensity parameters O_t(t=2, 4, 6) were obtained to be 3.90×10^-20, 2.03×10^-20, 9.03×10^-21cm², respectively. Then the radiative transition probabilities, radiative lifetimes and fluorescence branching ratio were calculated. Intense blue three-photon upconversion fluorescence and near-infrared two-photon upconversion fluorescence were investigated under the excitation of a 980nm diode laser at room temperature. 3. Sm³⁺—doped 5Li₂O-5K₂O-5BaO-10Bi₂O₃-75TeO₂ (LKBBT—Ⅱ) glasses with high refractive index have been synthesized. The absorption and fluorescence spectra of this glass were measured and analyzed. The absorption spectra was fitted by J-O theory, and intensity parameters O_t(t=2, 4, 6)were found to be 4.73×10^-20, 2.78×10^-20, 1.77×10^-20cm², respectively. Then the relative intensity of spectral lines of every energy level transition, radiative transition probabilities, radiative lifetimes and fluorescence branching ratio were calculated. In the Sm³⁺—doped bismuth tellurite glasses, Sm³⁺ emit intense reddish-orange lights under the excitation of long-wave UV and blue lights.4. Eu³⁺—doped LKBBT—Ⅱglass emit bright red lights under UV irradiation. The emission spectra of Eu³⁺ in LKBBT glasses under 395nm excitation exhibits the well-known emission bands centered around 587, 615, 652 and 703nm, and owing to the ⁵D₀→⁷F_J(J=1, 2, 3, 4) transitions, respectively. The most interesting feature obtained of emission spectrum is fluorescence from the higher ⁵D levels (⁵D₁, ⁵D₂ and ⁵D₃) have also been detected in the Eu³⁺ doped LKBBT glass. The 420nm, 431nm, 446nm, 466nm, 490nm, 513nm, 537nm and 556nm bands can be assigned to ⁵D₃→⁷F₁, ⁵D₃→⁷F₂, ⁵D₃→⁷F₃, ⁵D₃→⁷F₄, ⁵D₂→⁷F₂, ⁵D₂→⁷F₃, ⁵D₁→⁷F₁ and ⁵D₁→⁷F₂ transitions, respectively. This phenomena is rarely reported in other host material.These new phenomena and results of studies provide the theoretical basis and pledge of new material for new types of fluorescence display devices and development of rare—earth doped new laser glasses and fibres.