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We demonstrate the laser and thermal properties on the four Cr,Er:YSGG crystal rods with different diameters from 3 to 6 mm. A maximum pulse energy 1261 mJ operated at 5 Hz and 2.79 μm is obtained on the rod of 4 mm diameter, corresponding to electrical-to-optical efficiency of 1.53% and slope efficiency 1.82%, respectively. Combining with the electrical-to-optical efficiency and thermal distribution, the formula of the thermal focal length is modified further. The simulation results of the thermal focal length for four crystals with different diameters are in good consistence with the measurement values, suggesting the revised formula is accurate and effective to calculate the thermal focal length.

We demonstrated an improvement of laser performance by co-doping Cr3+ into Er:YAG crystal grown by the Czochralski method. The result of X-ray rocking curve suggested that the crystal had high crystalline quality. Two strong absorption bands centered at 450 and 596 nm indicated the Cr,Er:YAG crystal was more suitable for xenon lamp pumping. A maximum single pulse energy of 1.52 J was obtained on the Cr,Er:YAG crystal operated at 5 Hz and 2.94 μm, corresponding to the slope efficiency and electrical-to-optical efficiency of 1.80% and 1.28%, but those of the Er:YAG crystal were only 0.99 J, 1.31% and 0.83%, respectively. Therefore, the Cr,Er:YAG crystal may be a potentially mid-infrared radiation-resistant laser material with higher single pulse energy and efficiency.

Er,Pr:Y2.8Sc1Al4.2O12 (Er,Pr:YSAG) crystal has been successfully grown by the Czochralski method. The FWHM of XRC is 0.050°, indicating the high crystalline quality. Besides, thermal conductivity of the crystal is 5.76 W/mK, which is higher than lots of other heavily Er3+ doped crystals meaning the great potential in solid-laser gain media application. Luminescence characters of the crystal at 3 μm are investigated in detail to determine the laser generation potential. An intensive reduce is occurring on the fluorescence lifetimes of 4I13/2 energy level (0.75 ms) of Er3+ ions after Pr3+ ions co-doped, giving the enormous promotion on the multi-wavelength laser generation at 3 μm. Besides, the as-grown Er,Pr:YSAG crystal realizes the dual-wavelength laser generation at 2694 and 2825 nm for the first time, and an average laser power of 235 mW is realized. The M2 factor is used to quantify the laser output beam quality, which value are 1.65/1.56 along x and y axis, meaning a high-brightness laser generation of Er,Pr:YSAG crystal at 3 μm.

30 at% Er3+:GSAG single crystal was successfully grown by the Czochralski method. The dislocation of (111) face is studied using the chemical etching with the phosphoric acid etchant. The luminescence properties at 2.6–3.0 µm are systematically studied by measuring the fluorescence spectra and lifetimes to the transition of 4I11/2 → 4I13/2. The long fluorescence lifetime, high fluorescence intensity, and large gain σem spectra indicate that the 30 at% Er:GSAG crystal has the great potential for the multi-wavelength laser output at 2.6–3.0 µm. Meanwhile, the absorption and fluorescence properties of 30 at% Er:GSAG crystal under the gamma-ray radiation with three different intensities (35, 70, and 105 Mrad) have been investigated, indicate that this crystal can be considered as a promising MIR laser gain medium for being used under radiant environment. In addition, the luminescence property of 30 at% Er:GSAG crystal in visible and 1.5–1.7 µm was also studied, which shows the possibility to generate the laser around 1.6 µm.

We demonstrate a novel Er:LuSGG active gain medium emitting laser wavelength at 2795 nm for the first time. The Er:LuSGG crystal is grown successfully by the Czochralski method with high crystalline and optical quality. The spectra properties, including absorption and fluorescence emission cross-section are presented in contrast with similar Er-doped garnet crystals. The fluorescence lifetimes of the upper (4I11/2) and lower (4I13/2) laser levels are 1.75 and 4.64 ms, respectively. Under 973 nm laser diode pumping, a maximum output power of 789 mW in continuous-wave mode, corresponding to optical-to-optical efficiency of 20.2% and slope efficiency of 24.4%, is achieved with high laser beam quality. The results show that the Er:LuSGG is a promising MIR laser material operated at 2.8 µm.

Er3+ and Pr3+ co-doped YAP laser crystal with high optical quality was grown successfully by the Czochralski method for the first time. By contrast, an Er3+ single doped YAP laser crystal was also grown. The cell parameters of the two crystals were obtained by the X-ray Rietveld refinement method. The X-ray rocking curves indicate that the as-grown crystals possess excellent crystalline quality. The absorption spectra show that the crystals are suitable to be pumped by 972 nm LD. The NIR and MIR emission spectra, the up–conversion spectra and the fluorescence decay curves were also measured to investigate the influence of Pr3+ ions on the spectroscopic properties. The results indicate the Pr3+ ions acting as the deactivator can decrease efficiently the lifetime of the lower laser level 4I13/2 of the Er3+ ions from 10.72 to 0.489 ms, which would be beneficial to decrease the laser threshold and increase the laser conversion efficiency.

A new Cr 3+ , Yb 3+ , Ho 3+ , and Pr 3+ co-doped GYSGG (Gd 2 YSc 2 Ga 3 O 12 ) single crystal with a size of Φ 26 mm × 80 mm was grown successfully using the Czochralski method for the first time. Absorption spectrum is studied, and main absorption bands are centered at 449, 638, and 934 nm. The fluorescence spectrum shows a broad emission band around 2.8 µm, indicating the Cr 3+ and Yb 3+ ions can act as the sensitizer for the Ho 3+ ions. The fluorescence lifetimes of the 5 I 6 and 5 I 7 levels of the Ho 3+ ions are fitted to be 0.39 and 5.31 ms, respectively. By comparison with those of the Cr,Yb,Ho:GYSGG crystal, the Pr 3+ ions acting as the deactivator can decrease efficiently the lifetime of the lower laser level 5 I 7 of the Ho 3+ ions. Additionally, a flash lamp pumping 2.84 µm laser with maximum average power of 257 mW is achieved. These results indicate the Cr,Yb,Ho,Pr:GYSGG crystal is a new promising radiation-resistant laser gain medium applied in radiant environment.

High-temperature Raman spectroscopy has been applied to investigate in situ the solution structure near the BaBPO 5 crystal-solution interface. The experimental results show that [P 2 O 7 ] and [BO 4 ] are the basic structural units in BaBPO 5 -Li 4 P 2 O 7 high temperature solution, and [BPO 7 ] is the main growth unit of BaBPO 5 crystal. In the crystal growth boundary layer, the [P 2 O 7 ] and [BO 4 ] units are transformed into [BPO 7 ] unit. BaBPO 5 crystal growth process is considered as a connection process of growth unit [BPO 7 ] along c axis direction. According to the mechanism, the growth habits of BaBPO 5 crystal can be predicted.

Yb3+ and Ho3+ co-doped Lu2.55Y0.45Al5O12 (Yb,Ho:LuYAG) crystal with a size of Φ 28 mm × 120 mm was successfully grown by the Czochralski method. The lattice parameters of the as-grown Yb,Ho:LuYAG crystal were obtained by Rietveld refinement with the XRD data. The result of X-ray rocking curve indicated that the grown crystal has a high crystalline quality. From strong absorption band near 935 nm and emission bands within 2700–3000 nm, we found that the Yb3+ ions can be acted as the sensitizer for the activator ions Ho3+. Furthermore, the lifetimes of the 5I6 and 5I7 levels of the Ho3+ ions were 68.25 μs and 7.58 ms, respectively. These results indicated that the Yb,Ho:LuYAG crystal is a promising gain material for 2.91 μm laser pumped by a 940 nm LD.

In this paper we report on the structure of Na 3 VO 2 B 6 O 11 (NVBO) single crystals which were investigated by XRD, polarized Raman spectra in the range from 10 to 1600 cm −1 and infrared spectrum (IR) in the range from 100 to 1600 cm −1 . Factor group analysis has been used to study the full vibrational representation of the crystal. More than 120 phonon modes have been obtained, which are related to B O and V O vibration in the trigonal planar BO 3 triangle groups and tetrahedral BO 4 /VO 4 groups. The high frequency bands located at 1300–1415 cm −1 are assigned to stretching modes of the trigonal planar BO 3 groups. Moreover, intense Raman modes located at 631 cm −1 is related to BO 3 bending vibration as well. The weak band at 1158 cm −1 (A 1 mode) and strong band at 431 cm −1 (A 1 mode) are attributed to asymmetric stretching and bending vibration mode of tetrahedral BO 4 groups respectively. The vibrational band at 765–738 cm −1 in the Raman spectra of NVBO crystal maybe related to the breathing vibration of the boroxol ring consisting of two BO 4 tetrahedra. In addition, we assigned the intense band 900 (A 1 mode) and 831 cm −1 (B 2 mode) are relative to the v 1 symmetric stretching vibration of VO 4 tetrahedra. And the middle intense band at 382 (A 1 mode) and 385 (A 2 mode) are due to O V O vibration in VO 4 tetrahedra.

We demonstrate a 966 nm laser diode (LD) side-pumped Er,Pr:GYSGG laser crystal operated at 2.79 μm under a high repetition rate. The lifetimes of the upper level I11/24 and lower level I13/24 are 0.66 and 0.85 ms, respectively. The laser performance under different repetition rates and pulse widths is experimentally studied with the optimal cavity structure. A maximum output power of 8.86 W is achieved at 125 Hz and 200 μs pulse widths, corresponding to the slope efficiency of 14.8% and electrical-to-optical efficiency of 7.7%. With increasing frequency from 50 to 200 Hz, the slope efficiency varies from 24.7% to 11.7% operated at a 125 μs pulse width. Moreover, the Mx2/My2 factors of 7.52/7.59 and Θx/Θy far-field divergences of 16.1/16.5 mrad are also measured. The results indicate that a high-performance 2.79 μm laser could be realized on the Er,Pr:GYSGG radiation resistant crystal by deactivation and LD side-pumping.

A new laser crystal from Lu2.4Y0.6Al5O12 (LuYAG) co-doped with Cr3+, Tm3+, Ho3+, and Pr3+ ions was grown successfully by the Czochralski method for the first time. The structure parameters of the Cr,Tm,Ho,Pr:LuYAG crystal are determined by the X-ray Rietveld refinement method. The main absorption bands are observed near 426 and 782 nm, and the fluorescence spectrum excited by a 450 nm or 783 nm LD presents an emission band near 2.911 μm, indicating that the co-doped Cr3+ and Tm3+ ions can be utilized as sensitizers for the Ho3+ ions. The lifetimes of the 5I6 and 5I7 levels of the Ho3+ ions were measured and fitted to be 0.070 ms and 1.852 ms, respectively. The energy transfer efficiencies of the processes 5I6 (Ho3+) → 3F3,4 (Pr3+) and 5I7 (Ho3+) → 3F2 (Pr3+) + 3H6 (Pr3+) were calculated, showing that the Pr3+ ions can play the role of a deactivator for the Ho3+ ions. Furthermore, the energy transfer mechanisms among the Cr3+, Tm3+, Ho3+, and Pr3+ ions were studied. The results suggest that the Cr,Tm,Ho,Pr:LuYAG crystal is a new promising laser medium operating at around 2.9 μm under flash lamp or 783 nm LD pumping.

The performance of a laser-diode side-pumped Er:YSGG slab at a wavelength of 2.79 µm was investigated experimentally, and the laser output mode was analyzed using the theory of a thermally induced refractive index planar waveguide. Experimentally, a maximum continuous-wave output of 1.84 W with a slope efficiency of 11.2 %, and an optical-to-optical efficiency of 7.5 % at 2.79 µm was obtained with a 970-nm laser-diode dual-side-pumped Er:YSGG slab. To the best of our knowledge, the output power was the highest reported for a laser-diode-pumped Er:YSGG laser with a continuous-wave output at 2.79 µm. The numerical analysis showed that the output power was mainly limited by thermal effects in the thickness direction and the laser output transverse mode in the experiment was the fundamental mode in this direction.

The compounds formed from the Lu2O3–Ta2O5 system in the composition range 25–60 mol% Ta2O5 were prepared by solid-state reaction from 1350°C to 2058°C, and the phase transitions were investigated by X-ray diffraction (XRD). Cubic Lu3TaO7, M′-LuTaO4, M-LuTaO4, O-Ta2O5, and T-Ta2O5 are observed. With the temperature increase, there is an irreversible phase transition from M′ to M-LuTaO4 near 1770°C in the composition of 30–52 mol% Ta2O5, and another phase transition from T-Ta2O5 to O-Ta2O5 at about 1685°C when the ratio of Ta2O5 is >52 and ≤60 mol%. A phase diagram of the Lu2O3–Ta2O5 system in the range 0–100 mol% Ta2O5 was constructed. These results are helpful to explain the phase transition of Lu2O3–Ta2O5 system and design the preparation technique of LuTaO4 single crystal or ceramic scintillator, which may be applied in the fields of nuclear medicine and high-energy physics.

Lu2.4Y0.6Al5O12 (LuYAG) crystals with three different doping concentrations of Tm3+ and Ho3+ were grown successfully by the Czochralski method. The crystals exhibit broad absorption band at 783 nm and the full width at half maximum (FWHM) are about 11 nm. Excited by 783 nm laser diode (LD), strong fluorescence peaks are observed near 2.9 μm, suggesting that the Tm3+ ions can act as the sensitizer for Ho3+ ions. The stimulated emission cross-sections at 2.911 μm are calculated to be 5.49 × 10−18 cm2, 3.11 × 10−18 cm2, and 4.04 × 10−18 cm2, respectively. Compared with the Tm,Ho:LuAG, and Tm,Ho:YAG crystals, the Tm,Ho:LuYAG crystal with 3 at.% Tm3+ and 1 at.% Ho3+ has a relatively longer lifetime 0.138 ms for the upper level 5I6 and a shorter lifetime 7.25 ms for the lower level 5I7, which is advantageous to the population inversion. These results indicate that the Tm,Ho:LuYAG crystal with 3 at.% Tm3+ and 1 at.% Ho3+ is a new potential candidate for realizing the 2.911 μm laser output.

Yb,Ho:YAP and Yb,Ho,Pr:YAP laser crystals with high optical quality are successfully grown using the Czochralski method. The absorption coefficient and band width of the two crystals at 970 nm are increased because of the doping of Yb3+ sensitizer. The three strongest fluorescence peaks of the two crystals are located at approximately 2844, 2853, and 2912 nm, which correspond to the 5I6→5I7 level transitions of Ho3+ ions. Lifetime measurements indicate that the deactivator Pr3+ ions can efficiently decrease the lifetime of the lower level 5I7 from 8.848 ms to 1.258 ms. Energy-transfer mechanisms are also studied and analyzed, and up-conversion luminescence spectra provide the further evidence that Pr3+ ions can efficiently depopulate Ho3+ ions at the 5I7 level. All these results show that Yb,Ho,Pr:YAP crystal may be a promising laser medium for realizing 2.8–3.1 μm lasers pumped using a 970 nm laser diode.

We demonstrate the thermal analysis and laser performance of a GYSGG/Cr,Er,Pr:GYSGG composite crystal. The lifetime ratio of lower and upper levels of Er3+ in Cr,Er,Pr:GYSGG crystal is further reduced due to the optimized doping concentrations. The thermal effect of composite crystal is lower than that of Cr,Er,Pr:GYSGG crystal. A maximum pulse energy 342.8 mJ operated at 5 Hz and 2.79 μm is obtained on the composite crystal, corresponding to electrical-to-optical efficiency of 0.86% and slope efficiency of 1.08%. Under the same condition, these values on the Cr,Er,Pr:GYSGG crystal are only 315.8 mJ, 0.79% and 1.04%, respectively. Moreover, the composite crystal has also a relative high laser beam quality, exhibiting obvious advantage in reducing thermal effects and improving laser performances.

A great potential mid-infrared laser crystal of heavily Er3+ doped GSAG crystal with high optical quality is successfully grown by Cz method. The crystal quality of Er:GSAG crystal is determined by XRC. The structure parameters of Er:GSAG crystal are obtained by the X-ray Rietveld refinement method (a = b = c = 12.3196 A). The absorption cross section at 961 nm and 967 nm are 0.381 × 10−21 cm2 and 0.414 × 10−21 cm2, respectively. The 962 nm laser diode end-pumped Er:GSAG laser operated at 2828 nm is demonstrated for the first time. The performance of Er:GSAG laser is investigated in great detail. A maximum output power of Er:GSAG laser is 410 mW when pumped by 962 nm LD at 300 Hz and 0.5 ms. Simulating results display the highest temperatures of Er:GSAG laser spot is 345.8 K, indicating a small thermal lensing effect of Er:GSAG crystal. Besides, the laser performance of Er:GSAG crystals which irradiate by different doses of gamma-ray are used to investigated its potential for working in the radiation resistance environment. The results show the relatively minor differences on the Er:GSAG lasers performance, indicating a great potential of Er:GSAG crystal in radiant environment application.

A new Cr,Yb,Ho,Eu:YAlO3(YAP) laser crystal was successfully grown by the Czochralski method. Thermal properties were investigated along the a, b, and c crystalline axes. Results indicate that the Cr,Yb,Ho,Eu:YAP crystal has large anisotropic thermal expansion and that the suitable crystal growth direction is the b axis. The Debye temperatures were fitted, and the lattice vibration frequencies were calculated. Spectroscopic measurements show that Cr3+ and Yb3+ can be used as sensitizers of Ho3+ ions, and Eu3+ ions can play a role of the deactivator in decreasing the lifetime of laser lower level 5I7 from 8.69 ms to 1.89 ms, which is beneficial in decreasing laser threshold and increasing laser conversion efficiency. All these findings suggest that the Cr,Yb,Ho,Eu:YAP crystal is a new potential candidate for realizing 2.8–3 μm laser output pumped by a 970 nm laser diode or pulsed flash lamp.

A comparative study on the laser performance between bonding and non-bonding Er,Pr:GYSGG rods side-pumped by 970-nm laser diodes (LDs) is conducted for the thermal lensing compensation. The analyses of the thermal distribution and thermal focal length show that the bonding rod possesses a high cooling efficiency and weak thermal lensing effect compared with the conventional Er,Pr:GYSGG rod. Moreover, the laser characteristics of maximum output power, slope efficiency, and laser beam quality of the bonding rod with concave end-faces operated at 2.79 μm are improved under the high-repetition-rate operation. A maximum output power of 13.96 W is achieved at 150-Hz and 200-μs pulse width, corresponding to a slope efficiency of 17.7% and an electrical-to-optical efficiency of 12.9%. All results suggest that the combination of thermal bonding and concave end-face is a suitable structure for thermal lensing compensation.

We present a high-quality Cr,Nd:YAG crystal with 1.0 at. % Cr3 + and 1.1 at. % Nd3 + grown successfully by the Czochralski method. Spectroscopy results indicate that codoped Cr3 + ions are advantageous for improving pumping efficiency. The maximum average power of 20.24 W operated at 40 Hz and 1.06 μm is obtained on the Cr,Nd:YAG crystal, with electrical-to-optical and slope efficiencies that correspond to 3.00% and 3.77%. Meanwhile, the maximum average power of only 13.32 W is obtained on the Nd:YAG crystal, with the electrical-to-optical and slope efficiencies of 1.97% and 2.47%, respectively. In addition, the laser beam quality of the Cr,Nd:YAG crystal is comparative with that of the Nd:YAG crystal. Therefore, the Cr,Nd:YAG is a promising laser crystal with higher laser performance and stronger radiation-resistant ability than the Nd:YAG crystal. Thus, the Cr,Nd:YAG crystal can be applied to high-power systems and radiant environments.

BMBO (Ba2Mg(B3O6)2 crystal) is an excellent birefringent crystal and a potential stimulated Raman scattering (SRS) crystal. In this paper, high temperature Raman spectroscopy was used to in-situ study the melt structure near a BMBO crystal–melt interface. [B3O6]3− groups were found in this region. The result reveals that both of BaO bonds and MgO bonds are the weak bonds in the BMBO crystal structure. During the melting process, the crystal structure broke into Ba2+ ions, Mg2+ ions and [B3O6]3− groups. Our experimental results confirmed that the well-developed faces of BMBO crystals are the (001), (101) and (012) faces. Based on attachment energy theory, the crystal growth habit was discussed. The (001) (101) and (012) crystal faces linked by the weak BaO bonds and MgO bonds have smaller attachment energies and slower growth rates, and thus present in the final morphology. The (012) crystal face has a multi-terrace structure, which suggests that BMBO crystal grows with a layer-by-layer mode.

A continuous-wave (cw) 937 nm Nd:GYSGG laser based on the quasi-three-level transition 4F3/2 to 4I9/2 is reported. The output power of 0.80 W at 937 nm is achieved with the pump power of 8.2 W, corresponding to the conversion efficiency of 9.8%. The variation of output power and pump threshold with increased working temperature is also studied, which demonstrates the deterioration operation because of the serious reabsorption in a quasi-three-level Nd3+ doped laser.

Polycrystalline Yb:Gd 2 GeO 5 was prepared by solid state reaction method, and its structure, spectral properties, and energy structure were studied. The Yb:Gd 2 GeO 5 belongs to space group P2 1 /c, and its photoluminescence spectrum includes the range from 975 to 1088 nm which is one of the known broader emission of Yb 3+ . The broad emission spectrum is necessary for ultrashort laser operation and laser tuning. Crystal field parameters B q k and energy levels of Yb 3+ at two symmetry sites in Gd 2 GeO 5 were calculated by the simple overlap model, respectively. The calculated energy levels are consistent with the experimental very well. The energy splitting of Yb 3+ 2 F 7/2 ground state in Gd 2 GeO 5 is up to 1065 cm −1 . According to Boltzmann distribution, the thermal population ratio of the highest terminal laser level is about 0.605% and less than 2.32% of YAG by one order, which is very beneficial to population inversion. All results indicate that Yb:Gd 2 GeO 5 may be a promising laser crystal material for ultrashort and tunable all-solid laser.

Research on an efficient continuous-wave Nd:GYSGG laser at 1053 nm with excellent stability is demonstrated. The maximum output power is 4.17 W, corresponding to the conversion efficiency of 33.9% and the slope efficiency of 42.92%. Using a Cr:YAG absorber, pulsed dual-wavelength operation at 1053 and 1058.4 nm is obtained, of which the maximum single pulse energy and peak power are 172.1 μJ and 26.1 kW, respectively, when the pulse width is 6.6 ns and the repetition rate is 4.3 kHz. A polarization property is observed, owing to the anisotropy of Cr:YAG. This stably Q-switched dual-wavelength laser is a good pump source for the generation of a terahertz wave at 1.53 THz.

Ho:LuGG single crystal was successfully grown by the Czochralski growth method, and its lattice parameter was found to be 12.2371 A. Its thermal conductivity was measured to be 5.29 W mK −1 at 300 K. Meanwhile, transmission spectra were recorded at room temperature, and then its absorption spectra were obtained combining with the transmission spectra of LuGG crystal. The transition intensity parameters Ω t ( t = 2, 4, 6), the oscillator strengths, fluorescence branching ratios, transition probabilities and the lifetimes of Ho 3+ in LuGG crystal were all evaluated by the Judd–Ofelt theory. Furthermore, its emission spectra were also determined and analyzed.

The structure of borate melt has long been a fundamental unsolved problem in condensed matter physics, materials chemistry. Here, we use high temperature Raman spectroscopy and first principles calculations to study the structural change before and after the melting of a BiB3O6 crystal to obtain the BiB3O6 melt structure. A transformation of the 4-fold coordinated boron atoms to 3-fold coordinated boron atoms and a destruction of the atomic configuration around the Bi3+ ions were found when the crystal melted. Considering the growth habit of the BIBO crystal, we proposed a polymer model for the first time to describe the melt structure. The BiB3O6 melt is made up of special [B3O3O3] (O = bridging oxygen) structural units, which further polymerize into [B3O3O3]n chains by sharing oxygen atoms; the boron–oxygen chains are surrounded by the Bi3+ ions. Density functional theory (DFT) calculations were carried out to simulate the melt Raman spectrum based on the structural unit. The calculated BiB3O6 melt Raman spectrum shows good agreement with the experimental spectrum. The main vibrational bands were assigned. The strongest band below 400 cm−1 is mainly attributed to the wagging vibration of the side BOO2 triangle as a whole; the band located around 630 cm−1 is assigned to the bending vibrations of the [B3O3O3]n chain; the bands in the range of 1200–1500 cm−1 arise from the stretching vibrations of B–O (or B–O) bonds in the boron–oxygen triangles.

MoO3 is an important flux for lithium triborate (LiB3O5) crystal growth from high-temperature solutions. Although it has been widely used, the mechanism of the MoO3 flux-induced growth of LiB3O5 crystals is still not very clear. In this paper, we present a spectroscopic investigation of the Li2O–B2O3–MoO3 ternary glasses/solutions, which were prepared from high-temperature MoO3-based solutions for LiB3O5 crystal growth. By combining all the experimental data of Raman and MAS NMR, the types of structural species and the interactions between flux and solute are discussed to understand the MoO3 flux-reduced mechanism of LiB3O5 crystallization from the high-temperature solution. Considering the activities of lithium cations, an isomerization reaction is proposed to describe the structural evolution of the BO4 tetrahedron into the BO3 triangle in boroxol due to the MoO3 flux. The transition between the boron oxide species is essential for the LiB3O5 crystal growth. On cooling, the formed boroxol rings are polymerized by the re-formation of BO4 tetrahedrons again, and gather together to form the LiB3O5 crystal phase. Finally, the MoO3 flux-induced LiB3O5 crystallization may be elucidated with the decrease of the concentration of the BO4 tetrahedron in high-temperature solutions.

The single crystal Nd3+-doped in GdY2Sc2Ga3O12 (Nd3+:GYSGG) was grown by Czochralski method successfully, and its absorption spectra was analyzed in a wider spectral wavelength range at 7.6 K and 300 K, respectively. The free-ions and crystal-field parameters were fitted to the experimental energy levels at 7.6 K and 300 K with the root mean square deviation of 11.25 and 12.48 cm−1, respectively. According to the crystal-field calculations, 116 levels of Nd3+ at 7.6 K and 114 levels of Nd3+ at 300 K were assigned. The fitting results of free-ions and crystal-field parameters were compared with those already reported of Nd3+:GSGG and Nd3+:YSAG. The results indicated that the free-ions parameters are similar to those of the Nd3+ in GYSGG, GSGG and YSAG crystals, and the crystal-field interaction of GSGG and YSAG is stronger than that of GYSGG, which results in the dual-wavelength properties of Nd3+:GYSGG crystal.

The operating characteristics of a Nd:GYSGG laser in the 1.3 μm wavelength band based on the transition 4F3/2 → 4I13/2 is demonstrated. Using two different output couplers, single wavelengths operation at 1336 nm and dual-wavelength operation at 1321/1336 nm are obtained. The 1329 nm laser spectrum is also found when the pump level is relatively weak. The stimulated emission cross section of the 1336 nm laser line is estimated to be 1.12 time of that of the 1321 nm laser line. The output power of 1.98 W at 1336 nm is achieved with the pump power of 13.5 W, corresponding to the conversion efficiency of 14.7%. This is the first report on a 1.3-μm Nd:GYSGG laser to our knowledge.

The stimulated emission cross section of a 1.1-at.% doped Nd:Gd3xY3(1-x)Sc2Ga3(1+δ)O12 (x = 0 – 1, δ = –0.2 – 0.2) (Nd:GYSGG) crystal at 1.06 μm (4F3/2 → 4I11/2 transition) is measured at room temperature, using both the laser efficiency comparison method with an Nd:Y3Al5O12 (Nd:YAG) laser and the threshold formula method, with their results of 1.59×10-19 and 1.50×10-19 cm2, respectively. The measured results accord well with each other and they are of great use in designing a Nd:GYSGG laser system.

The mode-locking operation of the Nd:GGG crystal with a semiconductor saturable absorber mirror (SESAM) was demonstrated. Continuous wave (CW) mode-locking was obtained with the pulse duration of 11 ps and the pulse repetition rate of 40.38 MHz. At 7 W of pump power, the maximum average output power of 1.1 W was obtained with the slope efficiency of 18.1%.

The performance of continuous wave (CW) and passively Q-switched Nd:GYSGG lasers was investigated for the first time. The CW output powers of 4.2 W with dual wavelength of 1058.4 nm and 1061.5 nm were obtained under the diode pump power of 17 W with slope efficiencies of 26%. By using Cr4+:YAG wafer as saturable absorber, Q-switching operation was performed and the short pulse with pulse width of 6.6 ns was obtained with the peak power of 9.97 kW.

Nd:Lu3Al5O12 (Nd:LuAG) nano-crystalline was synthesized by co-precipitation method. Its phase transformation, structure, absorption and photoluminescence properties were studied. The Nd:LuAG polycrystalline phase is formed above 900 °C and its particle sizes are in the range of 18–36 nm. The structure of Nd:LuAG was refined by Rietveld method. The lattice parameters and the distortion of Lu3+–O2− polyhedron in Nd:LuAG are larger than that of in pure LuAG. Because the distortion of Lu3+–O2− polyhedron is larger than that of Y3+–O2− polyhedron in YAG and the distance of Lu3+–O2− is smaller than that of Y3+–O2− in YAG, Nd3+ in LuAG experiences a stronger crystal field effect, which is proved by the crystal field strength and the chemical environment parameter. The absorption spectrum shows that Nd:LuAG has a broad absorption band at 808 nm with FWHM above 6 nm, which is favorable for improving laser efficiency. The fluorescence lifetime from 4F3/2 → 4I11/2 transition is 320 μs and longer than that of Nd:YAG. The longer lifetime is propitious to energy storage. The emission cross section at 1064 nm is 2.89 × 10−19 cm2, taking into account the Boltzmann distribution of the excited state. The emission cross section in Nd:LuAG is also larger than that of Nd:YAG, which is useful for laser operation. All results indicate that Nd:LuAG is a promising crystal material to apply in high energy lasers.

A diode-pumped 937 nm Nd:GGG laser operating on the quasi-three-level under direct pumping at wavelength of around 882 nm is demonstrated, and its performances are investigated. A maximum output power of 358 mW at 937 nm was achieved at absorbed pump power of 4.8 W. The optical-to-optical conversion efficiency and the slope efficiency relative to absorbed power were 7.5 and 11.2%, respectively.

A Sm:GGG crystal was grown by the Czochralski method. The absorption and emission spectra of Sm:GGG were measured at room temperature. According to the Judd–Ofelt theory, the intensity parameters Ωt (t=2, 4, 6), spontaneous transition probabilities, branching ratio and radiative lifetime of 4G5/2 state were calculated. The emission cross-sections of 567, 613, 662 and 710 nm were estimated. The decay curve of the 613 nm emission assigned to the 4G5/2→6H7/2 transition was measured and the fluorescence lifetime was also determined.

The performance of passively mode-locked Nd:GYSGG lasers was investigated for the first time. The 1061.5 nm continuous wave (CW) mode-locking operation of the Nd:GYSGG crystal was achieved and pulse as short as 3.1 ps have been generated with a semiconductor saturable absorber mirror (SESAM). At the pump power of 7.39 W, the maximum average output power of 1.27 W was obtained with the slope efficiency of 18.9%. The pulse repetition rate of 42 MHz was obtained.

High quality Yb 3+ and Er 3+ co-doped Gd 3 Sc 2 Ga 3 O 12 (Yb,Er:GSGG) crystals were grown by the Czochralski (Cz) method, and their absorption and fluorescence properties with the gamma-ray radiation have been investigated. In comparison with Er:YAG crystals, these co-doped crystals exhibit much less color-center absorption after the illumination of gamma-ray. Excited by 940 nm LD, two of the strongest fluorescence peaks were observed near 2.7 and 2.8 μm, suggesting that the Yb 3+ can act as a sensitizer for Er 3+ ion in Yb,Er:GSGG crystals. In particular, the fluorescence intensity of these crystals does not deteriorate by the radiation of gamma-ray even with a dose of 100 Mrad, indicating that Yb,Er:GSGG possesses high capability for enduring the gamma radiation and is a potential laser gain medium for being used under radiant environment.

Yb 3+ doped phosphors with the wide photoluminescence band have attracted great attention recently due to their application in the ultra-short pulse laser pumped by laser diode. It was found that the full width at half maximum (FWHM) of photoluminescence of Yb 3+ :Gd 2 GeMoO 8 is up to 72 nm, which is desirable for the ultra-short pulse laser. Single crystals of (4.94 wt%) Yb 3+ -doped Gd 2 GeMoO 8 were grown by the flux method from MoO 3 self-flux. Transparent Yb 3+ :Gd 2 GeMoO 8 single crystals with dimension up to 4×3×3 mm 3 were grown successfully. The crystal structures of Gd 2 GeMoO 8 and Yb 3+ :Gd 2 GeMoO 8 were determined by Rietveld refinement to X-ray powder diffraction patterns, and their atom coordinates were obtained. The absorption and emission spectra of Yb 3+ :Gd 2 GeMoO 8 were measured at room temperature, their crystal field energy transitions were assigned. The fluorescence decay time of 1013 nm is determined to be 201.9 and 35.0 μs. Work indicates that Yb 3+ :Gd 2 GeMoO 8 is a potential laser material used in the ultra-short pulse and tunable all-solid-sate laser.

The fundamental properties of CdFe2O4 semiconductor thin film have been investigated. CdFe2O4 polycrystalline powder was synthesized by a co-precipitation–calcination process, and its thin film was prepared on a glass substrate by the pulsed laser deposition (PLD) method. The transmittance and reflectance spectra of the thin film indicate that the compound is an indirect bandgap material with E g = 1.97 eV. Its absorption coefficients are larger than 104 cm−1 when the wavelength is shorter than 700 nm. The electrical conductivity of the CdFe2O4 thin film was measured at different temperatures, its conductivity activation energy is about 71.9 meV. The relationship between CdFe2O4 semiconductor properties and its microstructure was discussed.

We demonstrate a laser diode (LD) end-pumped Er:YAP laser with dual-wavelength outputs of 2710 and 2728 nm. The maximum average powers of 739 and 738 mW are achieved in the continuous wave (CW) and pulse modes, which corresponds to optical-to-optical efficiencies of 10.1% and 12.3%, and the slope efficiencies of 12.1% and 13.8%, respectively. In addition, a comparison of laser performance on differently sized crystals indicates that the 1 × 1 × 5 mm3 Er:YAP crystal has a best cooling efficiency. This helps to decrease the thermal lensing effect, which contributes to improving laser efficiency and beam quality.

M-type GdTaO4 and Tb:GdTaO4 bulk single crystals were first grown by Czochralski method. Transmission, excitation, emission spectra and luminescence decay curves of them were measured. The refractive indices of GdTaO4 were calculated with its transmission spectrum and fitted with Sellmeier equation. GdTaO4 shows Gd3+ absorption and defect luminescence, Tb3+ exhibits its typical absorption and luminescence in GdTaO4. The luminescence decay times of GdTaO4 and Tb:GdTaO4 were also determined by fitting luminescence decay curves with single-exponential function.

Sm 3+ doped (Ca, Mg, Zr)GGG crystal has been grown by Czochralski technique. Its optical absorption, fluorescence and lifetime were studied. The refractive index and absorption cross-section were calculated. Judd–Ofelt theory was used to calculate the intensity parameters ( Ω t ), the spontaneous emission probabilities, the branching ratios, electric-dipole line strengths, magnetic-dipole line strengths and the radiative lifetime of the state 4 G 5/2 . The stimulated emission cross-sections at 566, 613, 649, and 709 nm were calculated. The decay curve of the 4 G 5/2 level of Sm 3+ ions with relatively low concentration (0.27 mol/L) was nearly single exponential and the experiment fluorescence lifetime ( τ exp ) was determined.

High-temperature Raman spectroscopy has been applied to investigate the melt structure near the BiB3O6 (BIBO) crystal–melt interface. Based on the experimental results, the crystal growth mechanism was proposed. (BOO)n (O = bridging oxygen atom) chains and free Bi3+ cations present in the BIBO bulk melt act as the crystal growth units. Bi-O bonds and [BO4]-tetrahedra were found near the BIBO crystal–melt interface. Two neighboring oxygen atoms in a (BOO)n chain or in two different (BOO)n chains are connected by the Bi3+ cations to form the structural prototype of BIBO crystal. Two adjacent (BOO)n chains are further connected to each other through the [BO4] tetrahedra to form the BIBO crystal structure. The predicted growth habit of the BIBO crystal is consistent with the observed one based on the mechanism.

X-ray powder diffraction is an indispensable technique to study material structure, phase transition and so on. It is necessary for high quality diffraction data to get high-precision diffraction angle. This work proposed four corrected functions of X-ray powder diffraction angle. Two methods, linearization method and modified Levenberg-Marquardt iteration method, are given to solve the function parameters, and the modified Levenberg-Marquardt method has fast convergent speed and stable solution. Two methods can give closed parameters, including those of Lu, Liu, and Chu functions and polynomial. New-corrected functions were used to fit the diffraction angle error of the tetragonal rutile polycrystalline TiO2 mixed with Gd0.45Y2.55Sc2Ga3O12 as a standard sample, and the computation result indicates that these functions can characterize the diffraction error very well. In some cases, the new-corrected functions can describe the diffraction angle error better than the reported corrected functions. At the same time, the lattice parameter of Gd0.45Y2.55Sc2Ga3O12 was computed with two methods. When the corrected function parameters and lattice parameters were solved by the least square method, the interaction of the function parameters and lattice parameters would result in great error. However, when the X-ray diffraction angles were corrected by corrected functions using a standard sample, the authentic lattice parameters can be obtained by the least square fitting.

Eu:Gd 3 Sc 2 Ga 3 O 12 powder was synthesized by co-precipitation method with metal Ga, Eu 2 O 3 , Gd 2 O 3 , Sc 2 O 3 as starting materials and aqueous ammonia as precipitator. X-ray diffraction (XRD), the Rietveld refinement method and transmission electron microscope (TEM) were employed to study the crystal structure. The fluorescent spectra and decay curves were used to investigate the luminescence properties of the resulting powders. The XRD spectra and results of the Rietveld refinement indicated that the structure of Gd 3 Sc 2 Ga 3 O 12 hardly changed and only crystal lattice distorted a little when Eu 3+ ion was doped. The transmission electron microscope (TEM) observation and XRD line broadening calculation revealed that the particle size of Eu:Gd 3 Sc 2 Ga 3 O 12 powder increased with the increase of the calcination temperature. At the same time, the emission intensity and lifetime of Eu:Gd 3 Sc 2 Ga 3 O 12 powder also increased with the calcination temperature. In the emission spectra, a 590 nm orange line from 5 D 0 → 7 F 1 as the most prominent group meaned that Eu 3+ ion mainly occupied the inversion center in Gd 3 Sc 2 Ga 3 O 12 crystal which may be caused by a small number of Gd atoms entered the 16(a) site.