Tunable luminescence between Stark levels of Pr3+ :YPO4 nanocrystals by different crystal phase

We report time-resolved second-order fluorescence between Stark levels of D-1(2) and H-3(4) in Pr3+:YPO4 nanocrystals with different crystal phase. Both intensity ratios of transition peaks between Stark levels and fluorescence lifetimes are modulated by phase composition and dressing effect. We have found that the maximum excitation peak shifts from yellow to orange-red region with continuous phase transformation from hexagonal phase to tetragonal phase, which is attributed to different multi-phonon relaxation rate induced by O-H group in hexagonal phase. The fluorescence lifetimes and intensity ratios of splitting peaks in time domain have also been effectively modulated by choosing excitation frequencies to resonate with different Stark levels. Both wavelength and time tunable luminescence has potential applications in biological labeling, imaging and solid state display devices.