The lattice environment of low phonon energy of strontium fluoride can suppress the energy loss caused by non-radiation process of trivalent lanthanide ions, so it is an ideal matrix material for active-ions doping. The fabrication and spectroscopic properties of SrF₂ transparent ceramics doped with trivalent lanthanide ions have attracted recent attention. Trivalent lanthanide ions tend to form clusters in SrF₂ crystal lattice, and the distance between ions shortens, resulting in energy exchange process and concentration quenching within these clusters, especially for rare-earth ions with a rich energy level structure. The concentration quenching effect leads to a reduction in luminescence intensity, and their applications are limited to a certain extent. Co-doping buffer ions into Pr:SrF₂ system is an effective solution to alleviate the concentration quenching of Pr³⁺ luminescence intensity. In this paper, Y³⁺ ions were selected as buffer ions. SrF₂ raw powder was synthesized by a chemical precipitation method, and Pr³⁺ and Y³⁺ ions co-doped SrF₂ transparent ceramic were fabricated in vacuum by a hot pressing (HP) sintering technology. The effect of Y³⁺ doping levels on the microstructure and luminescence spectroscopic characteristics of Pr, Y:SrF₂ transparent ceramics was discussed to regulate the luminescence properties of Pr³⁺ in SrF₂ transparent ceramics.

SrF₂ particles were synthesized by a chemical precipitation method with commercial strontium nitrate and potassium fluoride reagents. Cationic (Sr²⁺) and anion (F^-) solutions were prepared, and then separated via high-speed centrifugation after washing for three times. The as-synthesized SrF₂ particles were mixed with commercial available PrF₃ and YF₃ particles, where the doping level of PrF₃ was fixed at 3.0% and the level of YF₃ was varied from 0 to 10.0%. Pr, Y:SrF₂ transparent ceramics were fabricated in vacuum by a hot pressing sintering technology. The sintering temperature was 1 000 ℃, the pressure was 30 MPa and the holding time was 120 min. After the heat preservation, the ceramic samples were cooled to room temperature in the furnace, and the ceramics were polished on the both sides.

The transmittance and absorption spectra of the ceramics were determined by a UV-vis-NIR spectrophotometer, and the phase composition of the transparent ceramics was characterized by a X-ray diffractometer. The polished transparent ceramics were immersed in 6 mol/L hydrochloric acid solution and corroded at room temperature for 10 min. The microstructure of transparent ceramics was measured by a phenom Prox model scanning electron microscope. The luminescence spectra and fluorescence lifetime of transparent ceramics were measured by a fluorescence spectrofluorometer.

The diameter of Pr, Y:SrF₂ transparent ceramics is16 mm and the thickness is 2 mm. The lattice parameters of ceramics are gradually decreased after Sr²⁺ are replaced by the smaller Y³⁺. Pr, Y:SrF₂ ceramics co-doped with 0-5.0% YF₃ have the similar transmittance, and the maximum transmittance of the ceramics is close to 90%. The ceramic co-doped with 5.0% YF₃ has the maximum transmittance, and the transmittance at 400 nm wavelength is 90.1%, which is similar to the theoretical value. The transmittance of Pr, Y:SrF₂ ceramics decreases significantly with the increase of YF₃ co-doping level to 10.0%.

After YF₃ co-doping, the absorption capacity of the ceramic is enhanced, and the strongest absorption capacity is located at 443 nm. The ceramic has a dense microstructure without residual pores or impurity phase. The lattice distortion caused by the radius difference between Y³⁺ and Sr²⁺ promote the diffusion rate of ions at a high temperature and increase the average grain size of ceramics. ³P₂ states of Pr³⁺ are directly populated from ³H₄ ground states under light excitation at 443 nm, and then fall back to adjacent ³P₁, ³P₀ and ¹D₂ states through non-radiative relaxation, multiphonon relaxation and cross relaxation processes. These radiation transitions from generated high energy states to lower states forming different spectral bands. Y³⁺ break the cluster structure of Pr³⁺ , releasing more luminous centers, and reducing the energy transfer process within Pr³⁺, thus improving the luminous intensity. Y³⁺ co-doping causes the change of the local coordination environment around Pr³⁺, varying the transition probability between different energy states. The increase of the transition probability corresponds to the increase of the emission intensity. The proportion of emission band intensity to the total luminous intensity of Pr, Y:SrF₂ ceramics varies with the co-doping levels of YF₃, and the proportion of orange luminescence band intensity increases in the spectrum. The co-doping of Y³⁺ ions leads to serious distortion of SrF₂ lattice, decreases the symmetry of matrix structure, and accelerates the energy transition rate. The fluorescence lifetime of Pr³⁺ energy transition decreases with the increase of Y³⁺ co-doping level.

SrF₂ particles were synthesized by a chemical precipitation method, and Pr, Y:SrF₂ transparent ceramics were fabricated by a hot pressing technique. The ceramic co-doped with 5.0% YF₃ had the mximum transmittance, and the transmittance at 400 nm was 90.1%. As the co-doping level of YF₃ increased to 10.0%, the transmittance of Pr, Y:SrF₂ transparent ceramics decreased, and the average grain size increased to 200.1 μm. The co-doping of Y³⁺ ions into Pr, Y:SrF₂ transparent ceramics improved the absorption capacity of the ceramics. The absorption cross-sections of Pr:SrF₂ and Pr, Y:SrF₂ transparent ceramics at 443 nm were 3.59×10^-21 cm² and 1.13×10^-20 cm², respectively. The luminescence spectral properties of Pr, Y:SrF₂ transparent ceramics were regulated via changing the clusters and local coordination structures of Pr³⁺ in the matrix, and the luminescence of the ceramics gradually changed from reddish to orange-yellow. The lifetime of ³P₀→³H₄, ¹D₂→³H₄ and ³P₀→³F₂ transition decreased from 114.2, 100.4 μs and 91.8 μs to 28.6, 24.4 μs and 30.3 μs, respectively.