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.