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Al 2 O 3 –Y 3 Al 5 O 12 :Ce (Al 2 O 3 -YAG:Ce) eutectic with weak attenuation at high temperature has a wide range of applications in high-power white light solid-state lighting. However, the general color rendering index (general CRI, R a , the average value of R 1 -R 8) of phosphor-converted white light-emitting diode (Pc-WLED) based on this material is usually no higher than 70 (CCT < 6500 K). We grew Al 2 O 3 -YAG eutectics doped with three ions of Ce3+, Pr3+, and Cr3+ by the micro pulling-down (μ-PD) method to improve the R a through the co-luminescence and energy-transfer. The co-luminescence and energy-transfer were analyzed by the excitation-emission spectrum and the spectral power distribution. Results show that the energy-transfer between Ce3+ and Pr3+ ions in Al 2 O 3 -YAG:Ce, Pr occurs with each other, visibly enhancing the emission at around 610 nm and 694 nm, increases the R a by 8.4 compared to Al 2 O 3 -YAG:Ce. Moreover, the R a of the Al 2 O 3 -YAG:Ce and Al 2 O 3 -YAG:Cr stacked Pc-WLED increases by 20.4 compared to Al 2 O 3 -YAG:Ce, reaching 78.7. In addition, (R 9 , the special CRI for strong red, is 59.). In addition, the annealed (H 2) single-doped eutectics have little change compared to unannealed ones in luminescence, but the co-doped ones with multiple ions have a significant change. Significantly, the luminous efficiency of Al 2 O 3 -YAG:Ce after annealing is only increased by 4%, while that of Al 2 O 3 -YAG:Ce, Pr is increased by 13%. These studies show that the CRI of Pc-WLED base on Al 2 O 3 -YAG:Ce eutectic can be improved by ion co-doping in eutectic or superposition of Al 2 O 3 -YAG eutectic doped with other ions. • The co-luminescence of Ce3+ and Pr3+ in Al 2 O 3 –YAG enhancing the emission of 610 nm and 694 nm, increases the R a by 8.4. • The Cr3+ in Al 2 O 3 –YAG:Ce absorbs the emission spectra of the Ce3+ but quenches the fluorescence produced by Ce3+, which seriously hinders the luminescence of Ce3+. • The R a of the Al 2 O 3 –YAG:Ce and Al 2 O 3 –YAG:Cr stacked phosphor-converted LED increases by 20.4, reaching 78.7 (R 9 = 59). • The luminous efficiency of Al 2 O 3 –YAG:Ce after annealing is only increased by 4%, while that of Al 2 O 3 -YAG:Ce, Pr is increased by 13%. • It is found that the co-doping of Pr3+ ions will increase the probability of Ce4+ in Al 2 O 3 -YAG:Ce. [ABSTRACT FROM AUTHOR]

Ho,Pr:CaYAlO 4 (Ho,Pr:CYA) crystal doped with 1 at.% Ho3+ and 0.1 at.% Pr3+ was successfully grown using the Czochralski method. Polarized absorption spectra, emission spectra, and fluorescence lifetime measurements were performed. The impact of Pr3+ co-doping on the ∼3 μm emission of Ho3+ ions was analyzed. The energy transfer efficiency from Ho3+:5I 7 to Pr3+:3F 2 energy level was calculated to be 60.66 %, indicating that Pr3+ effectively mitigated the self-termination effect in Ho,Pr:CYA crystals. The absorption cross-section at 645 nm was found to be 1.53 × 10−20 cm2 for σ polarization and 2.62 × 10−20 cm2 for π polarization. The emission cross-section at 2842 nm was calculated to be 0.86 × 10−20 cm2 for σ polarization and 1.33 × 10−20 cm2 for π polarization at 2908 nm, with a full width at half maximum (FWHM) of 139 nm and 88 nm, respectively. The fluorescence lifetimes of the 5I 6 and 5I 7 levels were measured to be 0.17 ms and 2.01 ms, respectively. These results collectively suggest that Ho,Pr:CYA crystals hold great potential as a candidate for 2.8 μm laser applications. • Ho3+,Pr3+ co-doped CaYAlO 4 crystal was grown by the Czochralski method. • The crystal structure, polarized absorption and emission spectra were investigated. • The intensity parameters were obtained using J-O theory. [ABSTRACT FROM AUTHOR]

Tm3+-doped bismuth germanate crystals (Tm:BGO) with various doping concentrations of 0.5, 0.75, 1.0, 1.5, and 2.0 at.% were grown by the micro-pulling-down method (μ-PD). The effect of thulium concentration on the growth, structure, absorption spectra, emission spectra and fluorescence lifetime of 3H 4 and 3F 4 state was studied. Under excitation of 792 nm, Tm:BGO crystals exhibit two fluorescence bands corresponding to the 3H 4 → 3F 4 and the 3F 4 → 3H 6 transitions. The fluorescence lifetime of 3H 4 state decreased strongly as the thulium concentration increased, while the lifetime of 3F 4 state was relatively constant for all thulium concentrations. • Tm:BGO crystals with different Tm3+ concentration were grown by the micro-pulling-down method. • The effect of Tm3+ concentration on the growth, structure and spectroscopic properties of Tm:BGO crystals was studied. • Tm:BGO crystals exhibit two fluorescence bands corresponding to the 3H 4 → 3F 4 and the 3F 4 → 3H 6 transitions. [ABSTRACT FROM AUTHOR]

YScO 3 single crystal co-doped with Ho3+ and Pr3+ ions has been successfully grown by the Czochralaki method. The absorption spectrum, fluorescence spectrum and fluorescence decay curve were measured at room temperature. The absorption cross section of Ho,Pr:YScO 3 at 649 nm and 1130 nm was calculated to be 0.93 × 10−20 cm2 and 0.32 × 10−20 cm2, respectively. Judd-Ofelt (J-O) theory was performed to evaluate the spontaneous emission probabilities and the radiative lifetimes. Ho,Pr:YScO 3 exhibited strong emission at 2040 nm and 2890 nm with a emission cross section of 0.80 × 10−21 cm2 and 1.22 × 10−20 cm2, respectively. The fluorescence lifetime of the Ho3+:5I 6 and 5I 7 levels were calculated to be 0.31 ms and 5.89 ms, respectively. All the results indicate that the Ho,Pr:YScO 3 crystal could be a potential laser material for 2.9 μm laser operation. • Ho3+,Pr3+ co-doped YScO 3 was grown by the Czochralski method. • The crystal structure, absorption and emission spectra were investigated. • The effect of Pr3+ on the spectroscopic properties of Ho3+ was evaluated. [ABSTRACT FROM AUTHOR]

Pr3+-doped Sr 0.5 La 0.5 Mg 0.5 Al 11.5 O 19 (ASL) crystal along 〈100〉 direction was successfully grown using the Czochralski technique under azote atmosphere. Absorption and emission spectra of Pr:ASL crystal have been measured at room temperature. Continuous-wave laser operation of the a-cut and c-cut Pr:ASL samples under InGaN laser diode pumping has been demonstrated. For deep red laser operation at about 726 nm, the maximum output powers achieved from a-cut sample was 92.8 mW with slope efficiency of about 11.9%, while 46.6 mW with slope efficiency of 8.0% for the c-cut sample. For red laser at about 645 nm, maximum output powers of 49.2 mW and 42.8 mW were obtained for the a-cut sample and c-cut sample, corresponding to a slope efficiency of 6.7% and 8.5%, respectively. • Pr:Sr 0.5 La 0.5 Mg 0.5 Al 11.5 O 19 crystal was successfully grown using the Czochralski method. • Spectral parameters of Pr:Sr 0.5 La 0.5 Mg 0.5 Al 11.5 O 19 crystal were obtained. • Red and deep red laser were demonstrated in Pr:Sr 0.5 La 0.5 Mg 0.5 Al 11.5 O 19 crystal. [ABSTRACT FROM AUTHOR]

In this paper, the Floating zone technique was used to grow high-quality Cr3+:YScO 3 crystals. The absorption cross-sections of the 4A 2 →4T 1 transition and 4A 2 →4T 2 transitions were calculated to be 1.71 × 10−20 cm2 at 488 nm and 0.72 × 10−20 cm2 at 666 nm, respectively. The crystal field strength Dq, Racah parameters B, and C were calculated to be 1502 cm−1, 533 cm−1, and 3362 cm−1, respectively. In the Cr3+:YScO 3 crystal, the effective phonon energy and Huang-Rhys factor S were calculated to be 284 cm−1 and 8.62, respectively. The emission cross-section at 988 nm corresponding to the 4T 2 →4A 2 transition was calculated to be 1.44 × 10−20 cm2 with full width at half maximum (FWHM) of 318 nm. All the results show that Cr3+:YScO 3 crystal has the potential to be a tunable and ultrafast laser crystal. • Cr:YScO 3 crystals were successfully grown by the Floating zone technique(FZ) method. • Broad emission spectrum with full width at half maximum (FWHM) of 318 nm in Cr:YScO 3 crystals was observed. • Spectral properties and crystal field parameters of Cr:YScO 3 crystals were investigated and analysed. [ABSTRACT FROM AUTHOR]

A high-quality Cr:CYA (Cr:CaYAlO 4) single crystal fiber was grown by μ-PD (Micro-Pulling-Down) method. The E//a and E//c polarized excitation spectra of Cr:CYA at room temperature was measured. The crystal field parameters were calculated and the energy level structure of Cr:CYA was analyzed. We also measured the polarization emission spectra and lifetimes at different temperatures and calculated the effective emission cross-section. Based on the above data and Boltzmann law, the thermal distribution between the excited energy levels 2E and 4A 2 at different temperatures was analyzed. The present work may be useful for guiding laser research on Cr:CYA and other Cr3+-doped laser crystals above room temperature. • Cr:CYA single crystal fiber was grown by μ-PD (Micro-Pulling-Down) method. • Excitation spectra and crystal field parameters of Cr:CYA crystals were investigated and analyzed. • The effective emission cross section of Cr:CYA at different temperatures was calculated. [ABSTRACT FROM AUTHOR]