Upconversion color tunability and white light generation in Tm3+/Ho3+/Yb3+ doped aluminum germanate glasses

Tm3+/Ho3+/Yb3+ triply doped aluminum germanate glasses exhibiting multicolor upconversion fluorescences have been fabricated and characterized. Efficient three-photon blue upconversion emission of Tm3+ and two-photon green and red upconversion fluorescences of Ho3+ have been observed. The strong red emission of Ho3+, which is more than eight times higher than that of the green emission, is desirable in achieving high color rendering index. By varying the excitation power of the 974 nm wavelength laser diode, a series of white fluorescences with a large range of correlated color temperature (CCT) was obtained, and the fluorescence colors can be tuned from yellowish white to warm white, pure white, cool white, and bluish white with different CCT. The upconversion color tunability via pump power adjustment will promote the development of three-dimensional solid-state displays and upconversion illumination devices.