In this article, we report the preparation and luminescence properties of a series of novel rare-earth doped KBaY(MoO4)3 phosphors. The XRD patterns for the as-prepared samples have been assigned to the pure KBaY(MoO4)3 phase. The Tb3+, Eu3+ and Sm3+ singly-doped phosphors all show good luminescence properties with their characteristic excitations and emissions. We have optimized the rare-earth ion doping concentrations, yielding the compositions KBaY0.60(MoO4):0.40Tb3+, KBaY0.50(MoO4):0.50Eu3+ and KBaY0.96(MoO4):0.04Sm3+ with corresponding quantum yields of 15.80% (λex = 376 nm), 40.67% (λex = 392 nm) and 16.79% (λex = 402 nm), respectively. In addition, we have chosen co-doping of Tb3+/Eu3+ and Tb3+/Sm3+ into the host to realize tunable emission colors. We have observed energy transfer from Tb3+ to Eu3+ and from Tb3+ to Sm3+ ions in the as-prepared samples, which resulted in tunable emission colors from green to red and to orange-red under UV excitation, respectively. Moreover, investigation of the excitation and emission spectra, and decay lifetimes with increasing doping concentrations confirmed efficient energy transfer from Tb3+ to Eu3+ and from Tb3+ to Sm3+ ions in the co-doped samples. We also analyzed the energy transfer mechanisms between Tb3+ and Eu3+ and between Tb3+ and Sm3+ and both were determined to be dipole-dipole interactions. These results show that the as-prepared materials could serve as candidate phosphors for use in UV-pumped w-LEDs.

In this Article, we reported the synthesis and the upconversion luminescence (UCL) properties of a series of novel (Na/Li)­Bi­(MoO4)2:Yb3+,Er3+ [(N/L)­BMO:Yb3+,Er3+] and (Na/Li)­Bi­(MoO4)2:Yb3+,Ho3+,Ce3+ [(N/L)­BMO:Yb3+,Ho3+,Ce3+] phosphors. X-ray diffraction patterns and Rietveld refinements for several representative samples indicated the pure phase of as-prepared samples. The Yb3+,Er3+ codoped (N/L)­BMO presented bright green luminescence under 975 nm laser excitation with UCL spectra showing two main green bands around 529 nm (Er3+, 2H11/2 → 4I15/2) and 551 nm (Er3+, 4S3/2 → 4I15/2), in addition to a very weak one at 655 nm (Er3+, 4F9/2 → 4I15/2). The (N/L)­BMO:Yb3+,Ho3+ mainly showed a green band around 544 nm (5S2,5F4 → 5I8) and a red band around 654 nm (5F5 → 5I8) upon 975 nm laser excitation. With increasing Yb3+ concentrations in (N/L)­BMO:Yb3+,0.01Ho3+, the red/green ratios decreased monotonously corresponding to the emission color variation from light red to light yellow. Both UCL mechanisms of Yb3+,Er3+ and Yb3+,Ho3+ were determined to be two-phonons absorption processes in (N/L)­BMO:Yb3+,Er3+/Ho3+. The Ce3+ ions were introduced into Yb3+,Ho3+ codoped (N/L)­BMO to show the color tuning from light yellow to light red originating from the cross relaxation processes of (CR1) Ho3+ (5F4,5S2) + Ce3+ (2F5/2) → Ho3+ (5F5) + Ce3+ (2F7/2) and (CR2) Ho3+(5I6) + Ce3+ (2F5/2) → Ho3+ (5I7) + Ce3+ (2F7/2), which is based on the energy matching of Ce3+2F7/2-2F5/2 level pairs with Ho3+5I6-5I7 and 5F4,5S2-5F5 level pairs and confirmed by the decay times. These results suggest good UCL properties of (N/L)­BMO:Yb3+, Er3+ and (N/L)­BMO:Yb3+, Ho3+, Ce3+ materials, and color modulation is easily controlled by varying Yb3+ concentration and a cross relaxation process between Ce3+ and Ho3+, which provides efficient methods to regulate the emission color of UCL phosphors.

In this report, a series of tunable-emitting KBaY(MoO 4 ) 3 :Dy 3+ , Eu 3+ (KBYMO:Dy 3+ , Eu 3+ ) phosphors were synthesized via a Pechini-type sol−gel reaction approach. XRD and Rietveld refinement results confirm the pure phase of as-prepared materials. Upon 351 nm excitation, the optimal sample KBYMO:0.05Dy 3+ shows its two main characteristic emission bands around 488 and 573 nm, which correspond to Dy 3+ transitions 4 F 9/2 → 6 H 15/2 and 4 F 9/2 → 6 H 13/2 , respectively, in addition to a weak band around 660 nm originating from Dy 3+ 4 F 9/2 → 6 H 11/2 transition. In the excitation spectrum monitored at 573 nm, it is worth noting that there are two excitation peaks at 365 and 453 nm, matching with commercial LED chips. With the addition of Eu 3+ into KBYMO:0.05Dy 3+ , the energy transfer from Dy 3+ to Eu 3+ is elucidated, resulting in the tunable emission color from greenish-yellow to orange-red with increasing Eu 3+ content upon a 365 nm UV lamp excitation, which can be proved by analyzing the profiles of the excitation and emission spectra of Dy 3+ , Eu 3+ codoped KBYMO and the decay times of Dy 3+ . The energy-transfer mechanism is determined to be a quadrupole−quadrupole interaction according to Dexter theory and Reisfield's approximation. Moreover, the temperaturedependent luminescence property of representative KBYMO:0.05Dy 3+ , 0.10Eu 3+ is evaluated, which presents an emission intensity maintenance of 82.8% at 423 K relative to room temperature 298 K, showing its good performance. These results indicate that the as-prepared KBYMO:Dy 3+ , Eu 3+ phosphors may be a candidate component applied in UV w-LEDs.

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