Efficient energy transfer from Bi3+ to Mn2+ in CaZnOS for WLED application

A series of Bi3+ and Mn2+ co-doped CaZnOS phosphors with a tunable emission color have been synthesized by a high temperature solid-state reaction method. Their crystal structure, spectroscopic properties, energy transfer and thermal quenching have been investigated systematically. An intense blue-green emission band at 485 nm and a red emission band at 616 nm were observed at an excitation wavelength of 375 nm, owing to the P-3(1,0) -> S-1(0) transition of Bi3+ and the T-4(1)((4)G) -> (6)A(1)(S-6) transition of Mn2+, respectively. The tunable color from blue-green, white light to red light can be obtained by varying the Mn2+ ion concentration from 0.005 to 0.015 in CaZnOS:Bi3+. The decay time decreased from 642 to 273 ns with the Mn2+ ion concentration x increasing from 0.005 to 0.015, and the energy transfer efficiency eta(T) can reach up to 65% in the CaZnOS:Bi3+,0.015Mn(2+) phosphor. As the temperature increases from 300 to 420 K, the emission intensity is maintained at 67%, and the activation energy E-a is estimated to be 0.28 eV. An LED fabricated using CaZnOS:Bi3+,0.01Mn(2+) exhibited the chromaticity coordinates and corrected color temperature (CCT) of (0.338, 0.364) and 4655 K, respectively. These results validate the promising applications of the CaZnOS:Bi3+,Mn2+ phosphor in UV white LEDs.