Photoluminescence and energy transfer properties of a novel molybdate KBaY(MoO₄)₃:Ln³⁺ (Ln³⁺ = Tb³⁺, Eu³⁺, Sm³⁺, Tb³⁺/Eu³⁺, Tb³⁺/Sm³⁺) as a multi-color emitting phosphor for UV w-LEDs

Abstract

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.

Near‐ultraviolet light–induced dazzling red emission in CaGd2(MoO4)4:2xSm3+ compounds for phosphor‐converted WLEDs

“…Obviously, the monitored spectrum contained a broad absorption peak in the short wavelength range which was ascribed to the charger transfer (CT) transition of O 2− → Mo 6+ in the MoO 4 2− group. Aside from the CT band, four sharp absorption peaks located at 405 nm ( 6 H 5/2 → 4 I 13/2 ), 420 nm ( 6 H 5/2 → 4 G 9/2 ), 440 nm ( 6 H 5/2 → 4 I 15/2 ), and 480 nm ( 6 H 5/2 → 4 I 9/2 ), which were attributed to the featured absorption of Sm 3+ ions, were also recognized in the diffuse reflectance spectrum. Besides, there is relation between the optical band gap ( E g ) and the absorption factor ( α ), as demonstrated below:here hv denotes the phonon energy, n = 1/2, 2, 3/2, and 3 shows the direct, allowed indirect, forbidden direct, and forbidden indirect electron transition, respectively, and A refers to the coefficient.…”

“…As disclosed, the recorded excitation spectrum can be divided into two parts, that is, a broad excitation band and several narrow excitation peaks. In special, the broad excitation band in the range of 225‐350 was assigned to the charge transfer (CT) band arising from the transition of O 2− → Mo 6+ in the MoO 4 2− group, whereas the remanent peaks centered at around 365, 378, 405, 420, 440, and 480 nm were ascribed to the transitions of 6 H 5/2 → 4 D 3/2 , 6 H 5/2 → 4 P 7/2 , 6 H 5/2 → 4 L 3/2 , 6 H 5/2 → 4 G 9/2 , 6 H 5/2 → 4 I 15/2 , and 6 H 5/2 → 4 I 9/2 , respectively . Compared with other excitation peaks, the band located at approximately 405 nm, which belongs to the NUV region, had the strongest intensity, demonstrating that the studied samples can be excited by the NUV light.…”

A Guide to Brighter Phosphors‐Linking Luminescence Properties to Doping Homogeneity Probed by NMR

“…The processes operate over a distance called critical energy transfer distance R c which ranges from a few ångströms to a few nanometers. [17][18][19][20] Solid state NMR has been reported to be helpful for studying paramagnetic systems. [21][22][23][24][25][26] Especially, the distribution of paramagnetic dopants can be investigated by the spin-lattice relaxation time, [27][28][29][30] hyperfine shifts [31,32] and the line-broadening effect.…”

“…In terms of luminescence the radii of these spheres (big circles) could be interpreted as the critical energy transfer distance R c . The radii r 0 and R c are not the same but typical values fall into a similar range: Å – few nm …”

“…The role of energy transfer processes, which may happen between sensitizers or between sensitizer and activator, and from sensitizer to killer sites, can't be underestimated (Figure ) for a better understanding of how the dopant distribution relates to luminescence performance. The processes operate over a distance called critical energy transfer distance R c which ranges from a few ångströms to a few nanometers …”