Ambient-Pressure Stabilization of β-GdB3 O6 by Doping with Bi3+ and Color-Tunable Emissions by Co-Doping with Tb3+ and Eu3+ : The First Photoluminescence Study of a High-Pressure Polymorph

Rare-earth borates are good candidates for optical applications. To date, however, the high-pressure/high-temperature technique has produced a large number of novel borates with optical properties that have rarely been investigated due to the severe problem of substantial defects. We targeted the high-pressure polymorph of β-GdB₃ O₆ and synthesized three solid solutions of β-Gd_0.75-x Bi_0.25 Tb_x B₃ O₆ (0≤x≤0.75), β-Gd_0.75-y Bi_0.25 Eu_y B₃ O₆ (0≤y≤0.75), and β-Gd_0.50-z Bi_0.25 Tb_0.25 Eu_z B₃ O₆ (0≤z≤0.05) by using typical solid-state reactions at 820 °C. Here, the function of Bi³⁺ is to stabilize the high-pressure phase by lowering the synthetic temperature and being the sensitizer to promote the green and red emissions of Tb³⁺ and Eu³⁺ . The multiple energy transfer paths were investigated by using lifetime decay experiments and photoluminescent spectra, and both efficiency and mechanism were determined. Eventually, color-tunable and white emissions were achieved by rational doping of Bi³⁺ , Tb³⁺ , and Eu³⁺ into β-GdB₃ O₆ , that is, the CIE chromaticity coordinate for β-Gd_0.44 Bi_0.25 Tb_0.30 Eu_0.01 B₃ O₆ is (0.318, 0.365) with a correlated color temperature of 6101 K.

Sol–gel syntheses, luminescence, and energy transfer properties of α-GdB5O9:Ce3+/Tb3+ phosphors

Sol–gel prepared α-GdB₅O₉ is a good phosphor host with advantages including controllable preparation, the absence of concentration quenching and effective energy transfer.