Eu3+ and Tb3+ doped LiCaY5(BO3)6: Efficient red and green phosphors under UV or NUV excitations

Abstract

Eu3+ and Tb3+ are typical red and green-emitting photoluminescent (PL) activators and rare earth borates are well-known good PL hosts. In this contribution, a recently reported borate LiCaY5(BO3)6 was selected as the host to study the Eu3+ and Tb3+ photoluminescence systematically. LiCa(Y1-xEux)5(BO3)6 (0 ≤ x ≤ 1), LiCa(Y1-yTby)5(BO3)6 (0 ≤ y ≤ 1) and LiCa(Y0.88-zTb0.12Euz)5(BO3)6 (0.01 ≤ z ≤ 0.07) were synthesized by solid state reactions and the powder X-ray diffraction proved the high purity and crystallinity by quantifying the unit cell volume expansion when replacing Y3+ with Eu3+ and Tb3+. Charge transfer band and f-f transitions of Eu3+ in ultraviolet (UV) and near UV range are both intense because there exists a strongly noncentrosymmetric site in the host. Concentration quenching effect was also observed at x = 0.30 and 0.50 when excited by CTB and 392 nm, respectively. For Tb3+, strong f-d and weak f-f transitions were observed along with the typical green emission, and the concentration quenching occurs at y = 0.12 and 0.30, respectively. It is interesting to observe the Tb3+ to Eu3+ energy transfer in co-doped phosphors, thus the color tunable emissions from green to yellow, and to red were realized by manipulating the dopant concentrations. A preliminary trial to combine these borates with NUV LED chips gave typical red, green, and warm white lights, indicating the potentials as LED-pumped phosphors.