Highly thermostable white-emitting Ca9ZnK(PO4)7:Ce3+,Dy3+ single-phase phosphor with tunable photoluminescence and energy transfer

Host-sensitized borate phosphors ZnGdB5O10:Mn2+/Dy3+/Sm3+

Photoluminescence energy transfer is a good strategy to enhance the efficiency or tuning of emission colors. A phosphor host containing Gd3+ may facilitate the host-sensitization effect and transfer the so-absorbed photon energy to other activators. Zn1-xMnxGdB5O10 (0.005 ≤ x ≤ 0.07), ZnGd1-yDyyB5O10 (0.01 ≤ y ≤ 0.09), and ZnGd1-zSmzB5O10 (0.01 ≤ z ≤ 0.09) were synthesized via the traditional high-temperature solid-state method. A powder X-ray diffraction technique was employed to confirm the phase purity and successful doping. In all phosphors, by monitoring the characteristic emission of Mn2+, Dy3+ and Sm3+, the excitation spectra of all were found to contain the typical absorption belonging to Gd3+; in addition, the largely shortened fluorescence lifetimes of Gd3+ after Mn2+, Dy3+ or Sm3+ doping strongly proved the existence of the host-sensitization effect. Along with Gd3+-sensitization, Mn2+ doped at the Zn2+ site emits a close-to-ideal red light. Dy3+ and Sm3+ doped at the Gd3+ site emit close to white and orange light, respectively. The calculated internal quantum efficiency is 25.5% for Zn0.995Mn0.005GdB5O10, 17.0% for ZnGd0.97Dy0.03B5O10 and 17.4% for ZnGd0.97Sm0.03B5O10. The high thermal stability of the photoluminescent emission for Mn2+, Dy3+, and Sm3+ can be demonstrated through in situ high-temperature experiments, which suggest possible enhanced energy transfer efficiency at high temperatures.

Preparation and luminescence properties of Ba2P2O7:Dy3+, Ce3+ phosphors

In this paper, Ba_2-x-yP₂O₇:xDy³⁺,yCe³⁺ phosphors are synthesized by calcining the precursor via chemical co-precipitation. The phase structure, excitation and emission spectra, thermal stability, the chromatic performance of phosphors, and energy transfer from Ce³⁺ to Dy³⁺ are studied and discussed. The results indicate the samples keep a stable crystal structure as a high-temperature σ-Ba₂P₂O₇ phase with two different coordination of Ba²⁺ sites. Ba₂P₂O₇:Dy³⁺ phosphors can be effectively excited by 349 nm n-UV light and emit 485 nm blue light and a relatively stronger yellow light peaking at 575 nm, corresponding to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺, implying that Dy³⁺ mainly occupies the non-inversion symmetric sites. By contrast, Ba₂P₂O₇:Ce³⁺ phosphors exhibit a broadband of excitation peaking at 312 nm, and two symmetrical emission peaks at 336 nm and 359 nm from 5d¹→⁴F_5/2 and 5d¹→⁴F_7/2 transitions of Ce³⁺, showing Ce³⁺ should merely be presumed to occupy Ba1 site. After Dy³⁺ and Ce³⁺ are co-doped, Ba₂P₂O₇:Dy³⁺, Ce³⁺ phosphors exhibit the enhanced characteristic blue and yellow emission of Dy³⁺ with nearly equal intensity under excitation at 323 nm, meaning Ce³⁺ co-doping increases the symmetry of Dy³⁺ site as well as the sensitizer. Simultaneously, energy transfer from Dy³⁺ to Ce³⁺ is found and discussed. The thermal stability of co-doped phosphors was characterized and briefly analyzed. The color coordinates of Ba₂P₂O₇:Dy³⁺ phosphors fall in the yellow-green region near the white light, while the emission moves towards the blue-green region after the Ce³⁺ is co-doped.