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A Nd3+ doped Gd0.1Y0.9AlO3 crystal was successfully grown using the Czochralski method. The segregation coefficient of Nd3+ ions was found to be as large as 0.76 in Gd0.1Y0.9AlO3 host. Based on the Judd-Ofelt theory, the three intensity parameters Ω2,4,6, radiative lifetimes, branching ratios were calculated to analyze the absorption and emission properties of the as-grown crystal. It is found that the width of the absorption band at around 880 nm is 29 nm, indicating that the Nd:Gd0.1Y0.9AlO3 crystal can be pumped efficiently by laser diodes. Furthermore, the large full width at half maximum at 1083 nm and long fluorescence lifetime (189.53 μs) were obtained, which means that the Nd:Gd0.1Y0.9AlO3 crystal may be an attractive host for ultrashort pulse and tunable broadband lasers. Being pumped by an 880 nm laser diode, the laser operation of Nd:Gd0.1Y0.9AlO3 crystal at 1.0 μm was obtained for the first time. A maximum output power of 677 mW was obtained with the 10% output coupler, corresponding to an optical-to-optical conversion efficiency of 22.16% and a slope efficiency of 27.80%. All these results show that Nd:Gd0.1Y0.9AlO3 crystal is a new mixed laser host which is suitable for 880 nm laser diode pump.

In the work, the first principles calculation and low temperature spectra were utilized to investigate the modification on Nd3+ clusters in SrF2 crystal. The results show that structures of the clusters vary greatly and it depends on the ionic radius of rare-earth La3+, Nd3+, Gd3+ and Y3+. The cubic sublattice centers are stable in large size rare-earth La3+- and Nd3+-doped SrF2, and the square antiprism centers are more stable in smaller size Gd3+- and Y3+-doped crystals. It suggests that the square antiprism clusters become more stable with decreasing ionic radius in going from La3+, Nd3+, Gd3+ to Y3+, while the cubic sublattice centers become unstable. Based on the results, the mixed [Nd3+-La3+] and [Nd3+-Gd3+] clusters are also calculated. Stability of square antiprism clusters is improved with increasing concentration of Gd3+ in [Nd3+-Gd3+] clusters, and that weakened when codoped with La3+. The results reveal that characteristics of the mixed centers depend on species and contents of the ingredient rare-earth ions. Local environment of the active ions could therefore be modified by codoping the other rare-earth ions, which agreed well with the tunable absorption and emission spectra of Nd3+:SrF2 modified by La3+, Gd3+ and Y3+. The varied cluster structures provide us a methodology towards designing of new rare-earth-doped fluoride materials.

A Bi/Er co-doped PbF2 laser crystal was successfully grown. The use of Er3+ co-doping for enhancing the near-infrared emission in Bi/Er co-doped single crystal was obtained for the first time, to the best of our knowledge. The results show that compared with the single Bi-doped crystal, in Bi/Er co-doped PbF2 crystal, Er3+ can act as an effective charge compensation ion to promote the conversion from Bi2+ to Bi+, which would effectively enhance the NIR fluorescence emission of the Bi/Er doubly doped PbF2 crystal. Besides, it was demonstrated that two different Bi-related active centers (Bi (I) and Bi (II)) located around the NIR fluorescence emission peak of 1015 and 1080 nm. The results above strongly suggest that Bi/Er co-doped laser crystal may be an attractive gain host for developing NIR solid-state lasers.

The use of Nd3+ codoping for sensitizing the Er3+ ion and enhancing the ∼ 2.7 μm emission from transition of Er3+: I 11 / 2 4 → I 13 / 2 4 were investigated in the Er/Nd codoped Gd0.1Y0.9AlO3 (GYAP) crystal for the first time, to the best of our knowledge. The ∼ 2.7 μm emission characteristics and the energy transfer mechanism of the as-grown crystals were investigated in details. On one hand, it is found that the codoped of Nd3+ ion can act as an appropriate sensitizer for Er3+ ion in GYAP crystal, making the Er/Nd:GYAP crystal can be pumped by commercialized 808 nm laser diodes (LD). On the other hand, the Nd3+ ions can also act as a suitable deactivated ion for Er3+ ions with efficient depopulation effect on the lower laser level Er3+: I 13 / 2 4 for enhancing the ∼ 2.7 μm fluorescence emission, while having little influence on the upper laser level of Er3+: I 11 / 2 4 . With these favorable properties, the Er/Nd:GYAP crystal may become an attractive host for developing solid state lasers at around 2.7 μm under a conventional 808 nm LD pump.

The use of Ce3+ codoping for enhancement of the Er3+: 4I13/2 → 4I15/2 emissions were investigated in the Lu3Al5O12 (LuAG) crystal for the first time. The effect of Ce3+ codoping on the 1.50–1.67 μm photoluminescence of Er3+ was investigated in detail. It was found that Ce3+ greatly enhanced Er3+: 1.50–1.67 μm emission by increasing the non-radiative decay rate from the 4I11/2 to 4I13/2 of Er3+, leading to greater population accumulation in the 4I13/2 level. With the codoped of Ce3+ ion in Er:LuAG crystal, the lifetime of Er3+: 4I11/2 level decreases dramatically from 90 μs to 58 μs, while the lifetime of Er3+: 4I13/2 level remains almost unchanged. These results suggest that the Er/Ce: LuAG crystal may become an attractive host for developing solid state lasers at around 1.50–1.67 μm laser applications under a conventional 970 nm LD pump.

A Tm 3+ /Ho 3+ :NaGd(MoO 4 ) 2 crystal was grown by the Czochralski method. The XRD results matched standard data from JCPDS file, which accorded with scheelite structure with an I41/a space group. Thermal properties of crystal were analyzed by using the TG–DSC curve. The melting point and specific heat are 1182 °C and 0.5 J/g K at 300 K, respectively. The Spectral properties of the Tm 3+ /Ho 3+ :NaGd(MoO 4 ) 2 crystal were investigated, including room temperature absorption spectrum and fluorescence spectrum. The absorption cross-section of Tm 3+ at 796 nm is 4.33 × 10 −20 cm 2 with pertinent full widths at half maximum (FWHM) of 10 nm. The intensity parameters, spontaneous emission probability, fluorescence branching ratios and radiative lifetimes were calculated by Judd–Ofelt theory. The emission cross-sections are 1.47 × 10 −20 cm 2 and 1.36 × 10 −20 cm 2 for Tm 3+ at 1850 nm and Ho 3+ at 2000 nm respectively. The lifetime of 5 I 7 → 5 I 8 (Ho 3+ ) was 4.263 ms.

An efficient enhancement and broadening 3 μm luminescence in the Er/Ho/Pr: PbF2 crystal was obtained for the first time. The 3 μm emission characteristics and energy transfer mechanism of the as-grown crystals were investigated in details. It shows that the introduced Er3+ ion can not only act as a sensitizer for Ho3+ ion to allow the crystal to be pumped by a 980 nm laser diode, but also broaden the 3 μm fluorescence emission. Moreover, the Pr3+ ions can also act as a suitable deactivated ion for Er3+ and Ho3+ ions, bringing about the enhancing of 3 μm fluorescence emission. These results suggest that the Er/Ho/Pr: PbF2 crystal may have potential applications around 3 μm broadband lasers.