Optical Floating Zone Technique Research Articles

Spin switching in Er1-xSmxFeO3 (x = 0, 0.2) single crystals

We investigated spin-switching transitions in Er1-xSmxFeO3 (x = 0, 0.2) single crystals and variations in spin configurations with the applied field. The crystals were grown using the optical floating zone technique, and the magnetic properties were measured under field-cooled cooling (FCC) and field-cooled warming (FCW) protocols. The crystals exhibit field-dependent variation in the spin-switching temperature. In FCC, spin switching temperature increases with a magnetic field. However, in FCW, the spin-switching temperature (TSSW) rises initially with an increasing magnetic field, reaches a maximum value and later decreases when field strengths are high. We observe that spin switching depends not only on the magnitude of the externally applied magnetic field but also on the starting temperature of FCC. The magnetic and thermal history of the sample has a critical role in this phenomenon. A phase diagram (magnetic field-TSSW) constructed using the FCC and FCW data helps to illustrate various magnetic configurations. The FCC and FCW measurements in the a-direction of ErFeO3 at high fields (2T, 3T) suggest that spin switching, which involves the reversal of spins, does not occur. Instead, there is a change in the magnitude of the weak ferromagnetic moment, and rare earth spins below the compensation temperature (Tcomp).

Synthesis, disorder and Ising anisotropy in a new spin liquid candidate PrMgAl11O19

Here we report the successful synthesis of large single crystals of triangular frustrated PrMgAl11O19 using the optical floating zone technique. Single crystal x-ray diffraction (XRD) measurements unveiled the presence of quenched disorder within the mirror plane, specifically ~7% of Pr ions deviating from the ideal 2d site towards the 6h site. Magnetic susceptibility measurements revealed an Ising anisotropy with the c-axis being the easy axis. Despite a large spin–spin interaction that develops below ~10 K and considerable site disorder, the spins do not order or freeze down to at least 50 mK. The availability of large single crystals offers a distinct opportunity to investigate the exotic magnetic state on a triangular lattice with an easy axis out of the plane.

Optical properties of pure and Sn-doped β-Ga2O3 single crystals grown by optical float zone technique

High-quality single crystals of both pure and Sn:β-Ga2O3 single crystals weregrown using the optical floating zone technique and a comprehensive study of its luminescence and scintillation properties was carried out. The pure and Sn:β-Ga2O3 grown crystals were oriented along (100) by Laue diffraction pattern and its monoclinic structure was confirmed using a single crystal XRD. X-ray induced luminescence spectrum shows a maximum emission peak at 365 nm. The cut off wavelength was observed around 258 nm and the optical band gap was calculated to be 4.64 eV from UV–Vis-NIR transmission spectroscopy. The room temperature Raman spectra were recorded and the various vibration modes were investigated. Low temperature (10 to 300 K) and high temperature (325 to 675 K) TL measurements were carried out on X-ray irradiated crystals and its TL kinetic parameters such as activation energy (eV) and frequency factor (S) were calculated. Scintillation decay time profiles were measured for both pure and Sn-doped crystals under 137Cs γ-ray excitation. The calculated scintillation light output is 2300 Ph/5.5 Mev for Sn:β-Ga2O3 crystal under α-particle excitation from 241Am radiation source.

Bismuth chalcogenide topological insulators crystals grown by the optical floating zone technique

In this paper, two procedures for the growth of both binary and ternary single crystals of bismuth chalcogenides by optical floating zone technique are described. Detailed characterization has been carried out on a series of samples, i.e. Bi2SexTe3-x, with x = 0 and 0.9, and Bi2-xSbxSe3, with x = 0 and 0.15, to isolate high quality single crystals, essential for an accurate study of the physical properties of the materials. Systematic compositional and structural analysis on the samples grown by the two different procedures have been compared to infer the optimal growth parameters to obtain the largest possible single crystals. The c-axis lattice parameter of Bi1.85Sb0.15Se3 is reported here for the first time.

Growth and characterization of Dy1−xSmxMnO3 single crystals by optical floating zone technique

Dy1−xSmxMnO3 powders were synthesized by solid-state reaction and single crystals were grown using optical floating zone method for the full composition range 0 ≤ x ≤ 1.0. Energy dispersive x-ray spectroscopy (EDS) confirms the nominal composition for all the grown crystals of Dy1−xSmxMnO3. Rietveld refinement analysis using synchrotron X-ray powder diffraction data on powders obtained after crushing the crystals confirms the orthorhombic phase with Pnma space group for all the compositions studied. The lattice parameters and unit cell volume are shown to increase with increasing Sm3+ content at the Dy3+ site in DyMnO3. Magnetization measurements on Dy1−xSmxMnO3 single crystals reveal that the Sm3+ substitution systematically decreases the rare-earth ordering temperature (TDy3+).

Ultra-high Curie temperature transparent piezoelectric Bi doped Ca2Nb2O7 single crystals

Ca2Nb2O7 is a promising material for high-temperature piezoelectric applications due to its ultra-high Curie temperature, which makes it a suitable candidate for use in harsh environments. However, their piezoelectric performance needs improvement. Here, through chemical engineering methods, we have successfully grown Bi3+ doped Ca2Nb2O7 single crystals using the optical floating zone technique. The Ca1.94Bi0.06Nb2O7 single crystals achieved better high-temperature stability, transparency and a higher piezoelectric constant of 12.8 pC/N at 298 K and 20.0 pC/N at 660 K. In addition to the dopant effects, mechanisms for enhancing the piezoelectric properties of perovskite-like layer structure (PLS) materials have been identified, highlighting the significant contribution of the NbO6 octahedron and interlayer ions. These findings offers valuable insights into improving the performance of PLS materials, which is crucial for promoting their practical applications as high-temperature lead-free piezoelectric materials.

Quantum geometric spin frustration of antiferromagnetic CuFeO2 enables photocatalytic applications

Photocatalysis, containing a potential solution to the global crises of energy shortage and the greenhouse effect, has been studied extensively in recent years. The CuFeO2 (abbreviated as CFO) is a material with a Delafossite structure, and has also been widely studied because of its triangular lattice antiferromagnets. The triangular lattice composed of Fe3+ ions, along with strong antiferromagnetic spin coupling between the Fe3+ ions, leads to a geometric spin frustration. Furthermore, CFO is also a potential candidate for the photocatalytic material due to its narrow band gap of 1.1–1.6 eV, electrochemical stability in an aqueous environment, high charge carrier mobility, flat-band potential positioned at ∼ 1 eV, and contains an abundance of raw materials in the earth. In this study, we successfully grew the size and highly-quality CFO single crystals using the optical floating-zone technique. Powder x-ray diffraction (XRD) and Rietveld refinement indicate that the CFO is a rhombohedral structure with a space group of R3̅m, consisting of edge-shared FeO6 octahedron to form the FeO2 layer, and the Cu cations occupied between the two FeO2 layers. The core-level electron energy loss (EEL) spectra found the valence of Fe and Cu in CFO is +3 and +1, respectively. The low-loss EEL spectrum observed two volume plasmons at ∼5 eV and ∼23 eV contributed from the collective oscillation of Cu-O antibonding states σCu−O* and mixed nonbonding Cu 3dxy, σCu−O bonding states, and Fe-O, respectively, based on the density function theory calculation. The optical absorption spectrum measured the energy bandgap for CFO is about 1.5 eV. The Raman spectrum shows significant Eg and A1 g vibration modes corresponding to the in-plane Fe-O and out-of-plane Cu-O vibrations, respectively. Both magnetic susceptibility, χ(T), with the applied magnetic field along the c-axis and specific heat capacity reveal the two magnetic phase transition temperatures at low temperatures: TN1 = 13.5 K when transition from paramagnetic (PM) phase to partially disordered antiferromagnetic, and TN2 = 10.5 K when complete transition from partially disordered antiferromagnetic to antiferromagnetic phase. The additional calculation of magnetic entropy change is 0.15, which is roughly close to 0.2, meaning that only 1/5 of the Fe3+ spins are disordered when transforming from PM states to partially disordered at T < TN1 in this study. The presence of instantaneous ferromagnetic spin arrangement (↑↑↓) extends the residence time of H2O on the surface of CFO, facilitating electron exchange with CFO and promoting photocatalytic water splitting reactions.

Growth, structural characterization, DFT study, and magnetic properties of the NdAuIn crystal

A crystal of NdAuIn was successfully grown using the optical floating zone technique. Single-crystal and powder XRD studies confirmed that NdAuIn adopts a hexagonal ZrNiAl-type structure. Comparative analysis of the crystal morphology was performed using the Bravais-Friedel, Donnay-Harker (BFDH) model. DTA analysis revealed that the NdAuIn phase melts congruently at 1136°C. The DFT-calculated enthalpy of formation is −774.192 meV/atom. A thermal expansion coefficient α = 4.1(3) × 10−5 K−1 was derived from the single crystal XRD measurements at 100, 200, and 300 K. The Sommerfeld coefficient γ of 1.262 (mJ/mol × K2) derived from the DFT calculations and the distribution of the density of electronic states, predict metallic conductivity for NdAuIn. The analysis of the charge density difference and Bader charge analysis show that the NdAuIn compound might be treated as polar intermetallic with negatively charged [AuIn]n− and positively charged Ndn+ sublattices. Magnetization measurements with the field parallel and perpendicular to the six-fold axis of the crystal revealed that NdAuIn is a Curie-Weiss paramagnet down to 25 K with an effective magnetic moment of ∼3.62 μB/Nd, which corresponds to the Nd3+ ion. The compound exhibits antiferromagnetic ordering at TN ∼2.4 K.

Investigation of the effect of Cr co-doping on the refractive index, spectroscopic parameters and lasing of Nd:GdVO4 crystals

Cr co-doped (0.5, 1.0, 1.2 and 1.5 at.%) Nd (0.5 at.%):GdVO4 single crystals, used as laser gain medium, were grown by the optical floating zone technique to investigate the effect of Cr on the refractive index and spectroscopic properties. The ordinary (no) and extra-ordinary (ne) refractive index of 0.5 at.% Cr co-doped Nd:GdVO4 crystals was found to be lower than the 1.0 at.% Cr co-doped crystals, and thereafter it becomes almost constant up to 1.5 at.% of Cr co-doping. Further, the thermo-optic coefficient (dn/dT) of Cr co-doped Nd:GdVO4 crystals is positive with values ∼10−5/°C and the value is higher for ne compared to no for all the Cr doping concentrations. Further, the measured fluorescence lifetime of Nd ion decreases from 98 to 85 μs with the increase in Cr concentration. The Judd-Ofelt (JO) analysis revealed that the JO parameters for all the samples are Ω2 ∼9.6–10.6 × 10−20 cm2, Ω4 ∼6.5–7.0 × 10−20 cm2 and Ω6 ∼6.5–7.0 × 10−20 cm2. The radiative lifetime (∼100 μs) and emission cross section (∼3.2–4.1 × 10−19 cm2) are not affected significantly by the Cr co-doping. The investigation suggests that the inclusion of Cr ion in the crystal lattice does not deteriorate the overall spectroscopic properties of the Nd ions, thus Cr may act as an excellent activator for Q-switching in the Nd:GdVO4 laser gain medium. Further, the self Q-switching in the Cr co-doped Nd:GdVO4 laser element was demonstrated. A stable pulsed laser output at 1066 nm with power ∼105 mW, pulse width ∼477 ns and repetition rate ∼550 kHz was obtained in the 1.0 at.% Cr co-doped crystal.

Charge density wave and crystalline electric field effects inTmNiC2

Single crystals of ${\mathrm{TmNiC}}_{2}$ were grown by the optical floating-zone technique and were investigated by x-ray diffraction (XRD), thermal expansion, electrical resistivity, specific heat, and magnetic susceptibility measurements. Single-crystal XRD reveals the formation of a commensurate charge density wave (CDW) characterized by a CDW modulation vector ${\mathbf{q}}_{\mathbf{2}\mathbf{c}}=(0.5,0.5,0.5)$, which is accompanied by a symmetry change from the orthorhombic space group $Amm2$ to the monoclinic space group $Cm$, i.e., to a CDW superstructure which is isostructural with that of ${\mathrm{LuNiC}}_{2}$. For all transport and thermodynamic properties, anomalies related to a second order-type thermodynamic CDW phase transition are observed at around ${T}_{\mathrm{CDW}}\ensuremath{\simeq}375\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The large specific heat anomaly at ${T}_{\mathrm{CDW}}, \mathrm{\ensuremath{\Delta}}C\ensuremath{\simeq}6.2\phantom{\rule{4pt}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{mol}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$, together with noticeable changes in entropy and enthalpy related to the CDW transition, suggests that this point group symmetry breaking CDW phase transition affects more significant parts of the Fermi surface as compared to the incommensurate CDW transition of, e.g., ${\mathrm{SmNiC}}_{2}$ with no change in point group symmetry. The results on the antiferromagnetic and paramagnetic state of ${\mathrm{TmNiC}}_{2}$ obtained by the above macroscopic techniques were complemented by microscopic studies via inelastic neutron scattering. A crystalline electric field modeling of macroscopic susceptibility and magnetic specific heat and entropy contributions as well as microscopic neutron scattering data, reveal crystal field eigenstates and eigenvalues with a ground-state doublet of the Tm-$4f$ electrons, which is well separated by about 25 meV from exited states of the $J=6$ ground-state multiplet.

Crystal structure, dielectric and magnetic studies of pure and Sr substituted LaFeO3 single crystal grown by optical floating zone technique

The pure and strontium (Sr) substituted LaFeO3 polycrystalline samples were prepared through solid state synthesis process and good quality single crystals were successfully grown by four mirror optical floating zone technique for dielectric and magnetic measurements. The feed and seed rods were prepared by employing an external pressure of about 70 MPa and sintered at 1350 ⁰C on 12 h. The orthorhombic structure of the pure and Sr substituted materials were confirmed by powder X-ray diffraction analysis. The nonappearance of shoulder peaks in the Sr substituted LaFeO3 sample reveals single-phase crystal system without any sub-grain boundaries. The composition of the pure and substituted crystals was confirmed by EDS (energy dispersive X-ray spectroscopy) analysis. The dielectric studies were carried out on both samples in the temperature range from 300 to 900 K for the frequency range from 2.5 kHz to 125 kHz. The grown crystals show their Neel temperature at 742 K and the dielectric constant value increased for substituted LaFeO3 crystal. A colossal dielectric behavior and electrical conductivities were analyzed through dielectric studies. The activation energies of pure and Sr substituted LaFeO3 crystals were estimated to be 0.19 and 0.16 eV respectively. Magnetic properties of the developed crystals were tested by M-H loop. The M-T plot of Sr substituted LaFeO3 crystal was discussed with Zero field cooled (ZFC) and Field cooled (FC) modes for its potential magnetic application.

Investigation of Sn Incorporation in β-Ga2O3 Single Crystals and its Effect on Structural and Optical Properties

Undoped and Sn-doped β-Ga2O3 single crystals were grown by optical floating zone technique by varying the doping concentration of Sn from 0.05 wt% to 0.2 wt%. Uniform distribution of the dopant ions was achieved by heat treatment. The crystalline quality and the expansion of the lattice were observed from the PXRD. Raman spectra reveals the incorporation of Sn atoms into the lattice by replacing Ga in the octahedral site. The interplanar distance (d) was calculated as 2.39 Å from the HR-TEM micrographs. The transmittance was found to be decreasing from 80% to 78% as the concentration of Sn increases. The absorption spectra shows a cut off edge around 260 nm for undoped and 270 nm for all Sn doped samples. The bandgap obtained for undoped β-Ga2O3 was 4.36 eV. The doping of 0.05 wt% of Sn decrease the value of bandgap to 4.08 eV, but, for 0.1 wt% and 0.2 wt% Sn an increase in the bandgap value of 4.13 eV and 4.20 eV was observed respectively. The refractive index was found to be 1.96 at 500 nm wavelength. The increase in Sn concentration results in increase of the roughness from 1.116 nm to 3.511 nm.

Magnetodielectric effect and significant magnetoelectric coupling of Co3NiNb2O9 single crystal

A4B2O9 (A = Co, Fe, Mn, Ni, B = Nb, Ta) compounds with a corundum-type structure can host multiferroic phenomena and present magnetoelectric coupling to achieve manipulations of their ground states by external fields. High quality Ni-doped Co4Nb2O9 single crystals of Co3NiNb2O9 have been synthesized for the first time using optical floating zone technique. Co3NiNb2O9 exhibits an antiferromagnetic order at 32 K with an easy magnetization axis in the ab plane. Field-dependent magnetizations at 20 K along [100] and [120] directions have a slope change at 6 and 9 kOe, respectively, indicating a spin-flop transition or spin rotation in the ab plane. Temperature dependence of dielectric constants along [100] and [120] directions show a magnetic-field-induced peak near the antiferromagnetic transition, proving a sizable magnetodielectric effect. Pyroelectric currents along [100] and [120] directions also have a divergent behavior near the transition under magnetic fields, manifesting a magnetoelectric coupling effect. The electric polarization along [120] direction reaches 128 μC/m2 under a magnetic field of 40 kOe, larger than that in most phases of the A4B2O9 system.

Effect of Cr co-doping on the optical absorption and emission characteristics of Yb:YVO4 single crystals grown by OFZ technique

Cr co-doped Yb:YVO4 (Cr:Yb:YVO4) single crystals with concentrations of 1.0 and 1.5 at.% of Cr and 3.0 at.% of Yb were grown by the optical floating zone technique. X-ray diffraction analysis on the grown crystals revealed that the lattice parameters of Cr:Yb:YVO4 crystals do not depend on the Cr doping concentration. The dislocation etch pit density estimated from the etching study was found to be 103/cm2. The observed fringes of nearly uniform thickness and spacing in birefringence interferometry for [100] plate and conoscopy pattern for [001] plate indicate the compositional and optical homogeneity of the crystal. Further, the influence of the Cr doping concentration on the 2A1→2B2 transition (at ∼1100 nm) and 2A1→2E transition (at ∼640 nm) due to Cr5+ ion were analysed using two orthogonal polarized light with electric field perpendicular (π-polarization) and parallel (σ-polarization) to [001] axis. These absorption peaks of Cr ion were found to be sensitive to the polarization of incident light. The absorption transition 2A1→2B2 around 1100 nm are permitted for π-polarization and on the other hand, the absorption transition 2A1→2E at 640 nm are permitted only for σ-polarization. The characteristic broader absorption band around ∼1100 nm is of importance as it is useful for self-Q-switching in a laser gain medium. The absorption coefficient corresponding to Cr5+ ions at 1100 nm increases with the increase in Cr doping concentration. The band-gap for σ-polarized light is slightly higher than π-polarized light and decreases with Cr doping. The increase in the estimated Urbach energy (50–122 meV) with the increase in the Cr doping concentration confirms that the defect states close to the band edge increase thus decrease the band gap. Further the photoluminescence intensity is in-line with the absorption data and decreases with increase in the Cr concentration from 0 to 1.5 at.%.

Magnetic properties of the noncentrosymmetric tetragonal antiferromagnet EuPtSi3

We report a comprehensive study of single crystals of the noncentrosymmetric rare-earth compound EuPtSi$_{3}$ grown by the optical floating-zone technique. Measurements of the magnetization, ac susceptibility, and specific heat consistently establish antiferromagnetic order of localized Eu$^{2+}$ moments below the N\'{e}el temperature $T_{\mathrm{N}} = 17~\mathrm{K}$, followed by a second magnetic transition at $T_{\mathrm{N1}} = 16~\mathrm{K}$. For a magnetic field along the easy $[001]$ axis, the magnetic phase diagram is composed of these two phases. For fields applied in the magnetically hard basal plane, two additional phases emerge under magnetic field, where the in-plane anisotropy is weak with $[100]$ being the hardest axis. At the phase transitions, the magnetic properties exhibit hysteresis and discrepancies between differential and ac susceptibility, suggesting slow reorientation processes of mesoscale magnetic textures. Consistently, powder and single-crystal neutron diffraction in zero field identify magnetic textures that are modulated on a length scale of the order of $100~\textrm{\r{A}}$, most likely in the form of N\'{e}el-type antiferromagnetic cycloids.

Growth of brownmillerite Ca2Fe2O5 single crystals under air, oxygen and argon atmospheres using optical floating zone technique: a comparative study

Growth of brownmillerite Ca2Fe2O5 single crystals under air, oxygen and argon atmospheres using optical floating zone technique: a comparative study

Raman and Photoluminescence Spectroscopic Studies on Structural Disorder in Oxygen Deficient Gd2Ti2O7‐δ Single Crystals

AbstractRaman and photoluminescence spectroscopic studies on oxygen vacancy‐induced structural disorder in Gd2Ti2O7‐δ single crystals grown by optical floating zone technique under argon atmosphere are reported. The oxygen vacancies in Gd2Ti2O7‐δ wafers decrease with thermal annealing in air atmosphere. The full width at half maximum of X‐ray diffraction rocking curve decreases from 245 to 157 arcsec and the optical transmittance increases from 23% to 87% (at 1000 nm) upon post growth thermal annealing. Raman spectroscopic studies reveal a monotonic increase in intensity of O–Gd–O (Eg) and Ti–O (A1g) stretching modes with thermal annealing. Since these modes are associated with modulation of oxygen x parameter which is sensitive to Ti–O octahedron distortion, the increase in Raman intensity indicates an improvement in structural ordering of oxygen sub‐lattice in Gd2Ti2O7‐δ. Moreover, the photoluminescence studies also corroborate the Raman analysis in terms of reduction of structural defects associated with oxygen vacancies as a function of thermal annealing. This study demonstrates the effectiveness of using Raman spectroscopy to probe the structural disorder in Gd2Ti2O7‐δ crystals.

The structural and magnetic properties of single-crystal Gd4Ga2O9

The crystalline structures and magnetic and thermodynamic properties of a Gd4Ga2O9 single crystal grown with the optical floating zone technique have been investigated. Gd4Ga2O9 crystallizes in a monoclinic structure with the space group P21/c at room temperature. Temperature-dependent magnetic susceptibility measurements along the three crystallographic axes reveal a paramagnetic (PM) behavior between 2 and 300 K. A Curie–Weiss (CW) law fit was carried out and the CW temperature θCW and magnetic frustration parameter f were calculated; these suggest antiferromagnetic (AFM) interactions between Gd3+ spins and a strong magnetic frustration. The field dependence of the magnetization at 2 K further confirms the magnetic frustration characteristics. A distinct λ-shaped peak at 1.4 K in the heat capacity curves suggests a transition from the PM to AFM phase. The magnetic entropy is contributed solely by Gd3+ ions.

Studies on Schottky Barrier Diodes Fabricated using Single‐Crystal Wafers of β‐Ga2O3 Grown by the Optical Floating Zone Technique

β‐Ga2O3 is one of the most promising wide‐bandgap materials for optoelectronic applications as well as a conducting substrate for GaN‐based device technologies. Single crystals of undoped β‐Ga2O3 are grown by the optical floating zone technique utilizing compressed dry air as growth atmosphere. The properties of β‐Ga2O3 are highly anisotropic. Optimization of the processing recipe for wafers along different orientations suitable for device development is conducted. Structural, optical, and electrical properties of the wafers are determined. Efforts are made to fabricate Schottky diodes based on Pt/Ti/Au–β‐Ga2O3–Ti/Au device structures. Devices are fabricated on (−201) cut wafers. The device characteristics are discussed in detail.

Unusual absorption and emission characteristics of Cr co−doped Nd:GdVO4 laser gain crystal

Single crystals of Cr co-doped Nd (0.5 at%):GdVO4 with varied Cr concentrations of 1.0, 1.2 and 1.5 at% were grown in ambience having 10%, 20% and 25% oxygen by optical floating zone technique for the first time to the best of our knowledge. Lattice parameters were found to be unchanged with Cr doping concentration. The etch pit dislocation density was in the range of 103–104/cm2. The observed fringes of nearly uniform thickness and spacing in birefringence interferometry indicate the optical uniformity of the crystal across the cross-section. Further, the effect of the doping concentration and the growth atmosphere on the optical absorption, particularly for the 2A1→2B2 transition (at ~1100 nm) due to Cr5+ ion, was investigated using polarized lights (i.e., E ǁ [001] or π-polarized) and E ⊥ [001] or σ-polarized) and found to be polarization sensitive. The transition peak of Cr at 1100 nm are allowed only for π- polarization of light whereas the transitions at 650 nm are allowed only for σ- polarization of light. The absorption of Cr5+ ion increases at 1100 nm with the increase of oxygen ambience for the Cr concentration 1.2 and 1.5 at% and for the crystals with Cr concentrations of 1.0 at%, a reverse effect in the absorption of Cr5+ ion was observed. The broad absorption transition at ~1100 nm is important as it results in saturable absorption that is used for self-Q-switching application. In accordance with the absorption data the photo luminescence intensity increases for 1.0 at% Cr doping and decreases for the 1.2 and 1.5 at% Cr doping with the increase of oxygen percentage in the growth ambience respectively. The observation has important technical implication in context to saturable absorption application. It suggests that to attain the desired level of saturable absorption, the growth ambience and the concentration of Cr should be chosen in line with the result presented here.