Tuning of the emission color via energy transfer from Bi3+ to Eu3+ ion in the Eu3+, Bi3+ doped calcium germanate phosphor for warm white LEDs
In the lighting field, it is essential to seek the phosphor materials with tunable emission for warm white light-emitting diodes (wLEDs). Herein, we reported a new type of Eu3+, Bi3+ doped calcium germanate phosphor, which can exhibit a broad emission tuning from blue, white and to red. According to the XRD results, the structure purity of all as-obtained germanate phosphors are revealed to feature a trigonal structure with the space group of R3(No. 146). Structural analysis shows that the dopants of Eu3+ and Bi3+ should tend to substitute the Lu sites in the crystal host. The photoluminescence (PL) spectroscopy shows that the Eu3+ and Bi3+ ions can emit the blue emission and the red emission upon excitation at 297 nm and 393 nm, respectively. In view of the significant spectral overlapping between the excitation wavelength of Eu3+ and the emission wavelength of Bi3+, we study the energy transfer from Bi3+ and Eu3+ ion and reveal that the energy transfer is happened via an electric dipole–dipole (d–d) interaction. Remarkably, when the doping content of Bi3+ ions is fixed, changing the doping content of Eu3+ ions can induce the emission color tuning from blue, white and to red. To explain better the PL observation, a mechanistic pattern, which bases on the energy transfer from Bi3+ and Eu3+ ion, has been also constructed, which is expected to provide a general idea for achieving the energy-transfer-controlled tunable phosphor materials for phosphor-converted wLEDs.
We acknowledge the financial support from youth research talents’ growth support program of Yangtze Normal University. We would like to appreciate our associates, especially Deyin Zhang for their valuable contributions to our research program. We gratefully acknowledge many important contributions from the researchers of all reports cited in our paper.