Journal of Inorganic Materials, Volume. 38, Issue 3, 350(2023)

Spectroscopic and Yellow Laser Features of Dy3+: Y3Al5O12 Single Crystals

Jiaxue YANG1,2, Wen LI1,3, Yan WANG1,4、*, Zhaojie ZHU1,4, Zhenyu YOU1,4, Jianfu LI1,4, and Chaoyang TU1,4、*
Author Affiliations
  • 11. Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China
  • 22. College of Chemistry, Fuzhou University, Fuzhou 350116, China
  • 33. School of Materials Science and Engineering, Fuzhou University, Fuzhou 350116, China
  • 44. Fujian Science & Technology Innovation Laboratory for Optoelectronic Information of China, Fuzhou 350108, China
  • show less

    In recent years, yellow laser crystals have raised great attentions owing to their comprehensive applications in the fields such as laser display, laser medical treatment, light detection and ranging (LIDAR), Bose-Einstein condensates, and atomic cooling and trapping. With the development of commercial blue light LD, the direct pumping of Dy3+ doped laser crystals has realized yellow laser based on its transition 4F9/26H13/2. In this work, Dy3+: Y3Al5O12 (Dy: YAG) crystals with 0.5%, 1.0%, 2.0%, 3.0%, and 4.0% (atomic fraction) nominal concentration of Dy3+ were grown using Czochralski method, the reason of crystal crack was discussed. Based on Judd-Ofelt (J-O) theory, the J-O intensity parameters and utilization, and other laser parameters of Dy: YAG crystals with different doping concentrations were evaluated. The effect of the doping concentration of Dy3+ on the spectroscopic performances like fluorescence branching ratio, stimulated emission cross-section, quantum efficiency, were analyzed comprehensively. Among all the five crystals, 1.0% Dy: YAG has the largest stimulated emission cross-section for 582 nm yellow emission, an intense fluorescence intensity with the 447 nm excitation, and a longer decay time of 0.823 ms. The fluorescence intensity and stimulated emission cross-section of 2.0% Dy: YAG are slightly less than that of 1.0% Dy: YAG, but the former has a higher absorption coefficient. Hence, the spectroscopic analysis results show that 1.0% and 2.0% are the suitable concentrations of Dy3+ ion in YAG crystal for yellow laser operation by diode pumping. The continuous wave laser with peak at 582.5 nm and the maximum output power of 166.8 μW yellow laser operation were realized in 2.0% Dy: YAG crystal.


    The interest in Dy3+ doped optical materials is rapidly growing recently, and more and more researches about different Dy3+-containing materials were reported[1-5]. Dy3+ doped luminescent materials in the visible region are burgeoning due to peculiar emissions which differ from other RE (rare-earth) ions doped materials. Dy3+ is also the only RE ion with yellow emission in addition to Tb3+. Because of the strong yellow emission intensity which is several times of Tb3+ doping at the same doping concentration and wide emission band from 565 nm to 595 nm, Dy3+ doped single crystals are promising in the field of all-solid-state laser[6]. Generally, a yellow laser is used for the treatment of fundus diseases and dermatological disorders in medical treatments[7-8]. 578 nm laser can be used for a Yb optical clock that matches the 1S0-3P0 transition of the Yb atoms, and 589 nm yellow laser can be used as a sodium beacon laser[9-10]. Dy3+ shows absorption bands in both blue and UV (ultraviolet) regions that match the InGaN blue LD (laser diode). The yellow laser operation using Dy3+ doped single crystal was reported for the first time in 2012 and gives confidence to the researchers to focus on the yellow laser based on Dy3+ ion-doped crystals[11].

    In recent years, all types of Dy3+ doped single crystals are reported, which provide a sufficient number of references for comparison of the performances among different host materials[12-17]. Unfortunately, to our best knowledge, up to now yellow laser output using Dy3+ activated bulk crystal (not fiber laser) as a gain medium was achieved successfully only in several host materials[11,18 -20]. Y3Al5O12 (YAG) is a typical laser crystal with high mechanical strength which cannot be broken down easily during laser experiments. The higher phonon energy of YAG makes the population on 6H13/2 level could greater extent transfer to ground state 6H15/2 by non-radiative transitions. It is relatively easy to grow YAG crystal using the Czochralski method on account of the congruent melting property. It also has a low cost due to the relatively cheaper raw materials Y2O3 and Al2O3. The spectroscopic characteristics of 3.0% Dy3+: YAG crystal under 384 nm excitation were investigated by Pan, et al[21]. The spectroscopic properties of 3.0% Dy3+: YAG crystal grown by the micro-pulling-down method were reported by Xu[22]. In addition, Dy3+ doped single crystal could be applied in the display and lighting areas on account of the strong blue and yellow emissions in visible waveband, which makes the white emitting available. Yu, et al[23] grew the Gd3+/Dy3+ co-doped CaF2 crystal by the Bridgeman method and the tunable white light were obtained by changing the concentration of Gd3+. The research from Xu, et al[24] showed Dy3+/Eu3+ co-doped LiLuF4 single crystal had good optical features and thermal stability. A white light emitting under 355 nm excitation in the Dy3+: Gd3Sc2Al3O12 crystal was demonstrated by Ding, et al[25]. The 366 nm absorption band of Dy3+: Y3Al5O12 (Dy: YAG) matches the excitation wavelength of commercial GaN UV-LED chips. Compared with phosphor powders containing Dy3+ ion, a single crystal is free of impurity phases, has good uniformity of activated ions, which does not need epoxy resin packaging.

    Dy3+ concentration has a great influence on the fluorescence performance of Dy3+ doped crystals, and it is meaningful to choose the appropriate doping concentration of Dy: YAG crystal for luminescence and laser operation. The previous researches on Dy3+ doped YAG single crystals always concentrated on one crystal with a specific Dy3+ doping concentration, and there are only a few studies on the effect of doping concentration on the spectroscopic properties. In this work, the emission spectra of different doping concentration Dy: YAG crystals were contrasted at 447 nm excitation and the spectroscopic parameters were calculated and discussed. The laser properties of Dy: YAG single crystal as laser gain medium was presented.

    1 Experimental

    Y3-xDyxAl5O12 (x = 0.015, 0.03, 0.06, 0.09, and 0.12) polycrystalline powders were synthesized by high- temperature solid reaction method. Dy2O3, Y2O3, and Al2O3 were weighted and mixed according to the stoichiometric ratio and pressed into tablets for sintering. After the sintering process, they were put into an Ir crucible for crystal growth. Yttrium aluminum garnet crystals with different Dy3+ concentrations (0.5%, 1.0%, 2.0%, 3.0%, 4.0%, atomic fraction) were grown using the Czochralski method under a high purity N2 atmosphere. To eliminate the defects in the crystals and release the stress, such crystals were annealed in the air. An image of as-grown crystals is presented in Fig. 1.

    Photos of the as-grown single crystals

    Figure 1.Photos of the as-grown single crystals

    The Dy3+ concentration of the upper part of the crystals was measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES, Ultima2, Jobin- Yvon). Powder X-ray diffraction (XRD) was characterized on an X-ray diffractometer (Miniflex-600, Rigaku) in step scan mode. The absorption spectra of the samples with a size of 10 mm×10 mm×1 mm were recorded by a UV-VIS-NIR spectrometer (Lamda-980, Perkin-Elmer). The emission spectra and decay curves were measured by a fluorescence spectrometer (FLS980, Edinburgh Instruments). The pump source was a diode laser with the central wavelength of 447 nm and maximum output power of 3.58 W. The laser cavity consisted of two mirror with high transmission (>96%) at 447 nm and high reflection (>99.7%). The 2.0%Dy:YAG crystal with the size of 5 mm×5 mm×10 mm was wrapped with the indium foil and put on the thermos electric cooler.

    As seen in Fig. 1, there appeared bubbles and crack in 4.0%Dy: YAG crystal which was grown at first in this work. The appearance of bubbles and crack might stem from the impure polycrystalline powders. To avoid the impaction of impurity phases, we used higher purity of raw materials and extended the grinding time to make the mixture more homogeneous. High quality seed crystal was also used to inhibit the defects of crystals. Furthermore, some measurements were taken such as slowing down the rate of heating and keeping the temperature above the melting point 100 ℃ for several hours, to make sure the polycrystalline melt completely which eliminated gas bubbles effectively. Changing the temperature field around crucible could improve this situation efficiently too. To strengthen the insulation, the gap between zirconia cylindrical thermal insulation materials and crucible was filled with zirconia powders. At the same time, double-layer zirconia cylinder was used to prevent crystal cracking during annealing.

    2 Results and discussion

    2.1 Absorption spectra and Judd-Ofelt (J-O) analysis

    Absorption spectra of Dy: YAG crystals measured at room temperature are depicted in Fig. 2, which indicates that the absorption coefficient (α) is proportional to the Dy3+ concentration. With an increase in doping concentration, the peak wavelengths of absorption bands are almost unchanged. Peaks at 353, 366, 386, 447, 479, 752, 804, 897, 1073, 1291, and 1687 nm correspond to the transitions from the ground state 6H15/2 to 6P7/2+4I11/2, 6P5/2+4M19/2, 4K17/2+4M21/2+4F7/2+4I13/2, 4I15/2, 4F9/2, 6F3/2, 6F5/2, 6F7/2, 6H7/2+6F9/2, 6H9/2+6F11/2, and 6H11/2 upper-states, respectively.

    Absorption spectra of Dy: YAG crystals

    Figure 2.Absorption spectra of Dy: YAG crystals

    Following the ICP-AES results, the segregation coefficient of Dy3+ in each crystal is calculated as the ratio of its concentration in the crystal and melt. Obtained results are given in Table 1. The effective segregation coefficient of Dy3+ in each crystal is about 0.48, which is in agreement with the previous report[21].

    • Table 1.

      Concentration, effective segregation coefficient and absorption cross-section of Dy3+ in YAG crystal

      Table 1.

      Concentration, effective segregation coefficient and absorption cross-section of Dy3+ in YAG crystal

      Crystalc/% (in atomic) keffNc/cm-3α/cm-1σabs/cm2
      0.5% Dy: YAG0.2390.4783.31×10190.0551.66×10-21
      1.0% Dy: YAG0.4790.4796.61×10190.1031.56×10-21
      2.0% Dy: YAG0.9700.4851.33×10200.2151.61×10-21
      3.0% Dy: YAG1.4270.4751.95×10200.3381.73×10-21
      4.0% Dy: YAG1.9750.4942.69×10200.4301.60×10-21

    Next, absorption cross-section (σabs) at 447 nm is obtained using the formula:


    Where α is absorption coefficient and Nc is the amount of Dy3+ ions per cm3.

    The σabs of Dy3+ in YAG is ~1.6×10-21 cm2 as presented in Table 1. The theoretical and experimental line-strengths of Dy: YAG are obtained utilizing J-O theory[26-27]:


    Where Ωt(t=2, 4, 6) are the J-O intensity parameters, and Ω2 is related to the symmetry of Dy3+ and the chemical bond between Dy3+ and O2-. Here, ║U(t)║ is the squared reduced matrix elements of the tensorial operator, which has been calculated by Carnall in Ref. [28]. n is refractive indices which are calculated by the Sellmeier equation for YAG crystal[29]. The values of Planck constant (h), speed of light (c), and electron charge (e) are 6.626×10-27 erg∙s (1 erg∙s =10-7 J∙s), 2.998×1010 cm∙s-1, and 4.803×10-10 esu (1 A=3×109 esu), respectively. λ¯is average wavelength of absorption band for JJ′ transition, and L is length of the crystal in the light pass direction.

    The value of root-mean-square (RMS) is evaluated as:


    Where Sexp and Scal are the line-strengths of the experimental and theoretical data respectively, and N is the number of absorption bands used for calculation. The three J-O intensity parameters of the studied crystals are fitted and the above parameters are all given in Table 2.

    • Table 2.

      Experimental line strength, calculated line strength, and J-O intensity parameters of Dy: YAG crystals

      Table 2.

      Experimental line strength, calculated line strength, and J-O intensity parameters of Dy: YAG crystals

      6H15/2 λ¯/nm n0.5%Dy: YAG1.0%Dy: YAG2.0%Dy: YAG3.0%Dy: YAG4.0%Dy: YAG
      Sexp/(×10-20, cm2) Scal/(×10-20, cm2) Sexp/(×10-20, cm2) Scal/(×10-20, cm2) Sexp/(×10-20, cm2) Scal/(×10-20, cm2) Sexp/(×10-20, cm2) Scal/(×10-20, cm2) Sexp/(×10-20, cm2) Scal/(×10-20, cm2)
      RMS/(×10-20, cm2)0.1800.2300.2370.2460.226
      Ωt(t=2, 4, 6)/(×10-20, cm2)Ω2=0.793Ω4=1.284Ω6=2.634Ω2=0.747Ω4=1.520Ω6=2.825Ω2=0.498Ω4=2.155Ω6=2.848Ω2=0.312Ω4=2.674Ω6=2.887Ω2=0.142Ω4=2.573Ω6=3.011

    Later, J-O intensity parameters Ωt are used to obtain the radiative transition rates from the excited state 4F9/2 to lower states which comprise both electric dipole (Aed) and magnetic dipole (Amd) transitions in some cases. Aed and Amd values are computed using formulae:


    Where Aed and Amd are the radiative transition rates contributed by electric-dipole and magnetic-dipole transitions, respectively. Here, the emission transition matrix of Dy3+ ion ║U(t)║ and Smd values are quoted from Ref. [30].

    The fluorescence branching ratios (β) and the radiative lifetime (τr ) of the 4F9/2 level in the investigated crystals are obtained using expressions:


    Spontaneous emission transition rate (A) and fluorescence branching ratio (β) of 4F9/2 to lower levels are listed in Table 3. β of yellow emission which corresponds to 4F9/26H13/2 transition is in the range of 46%-50% for Dy: YAG crystals, which indicates that the yellow emission has considerable potential value in them.

    • Table 3.

      Spontaneous emission transition rate (A) and fluorescence branching ratio (β) of Dy: YAG crystals

      Table 3.

      Spontaneous emission transition rate (A) and fluorescence branching ratio (β) of Dy: YAG crystals

      4F9/22S+1LJ0.5%Dy: YAG1.0%Dy: YAG2.0%Dy: YAG3.0%Dy: YAG4.0%Dy: YAG
      A/s-1β/% A/s-1β/% A/s-1β/% A/s-1β/% A/s-1β/%
      6H7/2 +6F9/254.735.9659.106.0449.396.7156.137.1955.447.10

    2.2 Fluorescent characteristics

    Emission spectra of all samples under 447 nm excitation wavelength are shown in Fig. 3(a). Luminescence band peaks at 484, 582, 676, and 761 nm are corresponding to transitions from 4F9/2 to 6H15/2, 6H13/2, 6H11/2, and 6H9/2+ 6F11/2 lower levels, respectively. The luminescence intensity and the fitted 4F9/2 level lifetime with different doping concentrations at 447 nm were plotted in Fig. 3(b).

    Emission spectra of YAG crystals with different Dy3+ concentrations excited by 447 nm (a) and variation of intensity of 582 nm and 4F9/2 level lifetime with Dy3+ concentrations in Dy: YAG crystals (b)

    Figure 3.Emission spectra of YAG crystals with different Dy3+ concentrations excited by 447 nm (a) and variation of intensity of 582 nm and 4F9/2 level lifetime with Dy3+ concentrations in Dy: YAG crystals (b)

    Further, quantum efficiency (η) is defined by η = τ/τr, where, τr is 4F9/2 level radiative lifetime, τ is 4F9/2 level lifetime. The stimulated emission cross-section (σem) can be obtained by Füchtbauere Ladenburg formula[31-32] as:


    Where λ, n, c, and A(JJ) have their usual meanings. The value of σemτ is calculated and it is inversely proportional to the laser threshold[33]. All related spectroscopic parameters are contrasted with other Dy3+ doped crystals. σem at 582 nm of as-grown Dy: YAG crystals are found to be in the range from 2.36×10-21 to 2.71×10-21 cm2. The obtained results in all samples are listed in Table 4.

    • Table 4.

      Emission property parameters of Dy3+ in YAG and other crystals

      Table 4.

      Emission property parameters of Dy3+ in YAG and other crystals

      Crystalτr(4F9/2 level)/ms τ(4F9/2 level)/ms σem for yellow emission/(×10-21, cm2) σemτ/(×10-21, cm2∙ms) η/% Ref.
      0.5%Dy: YAG1.0900.8942.362.11082.02This work
      1.0%Dy: YAG1.0220.8232.712.23080.53
      2.0%Dy: YAG0.9990.6882.661.83068.87
      3.0%Dy: YAG0.9740.5712.541.45058.62
      4.0%Dy: YAG0.9720.4712.491.17048.46
      1.0%Dy3+: Gd3Ga3Al2O120.5960.5733.201.83496.14[13]
      3.0%Dy3+: Lu2O30.7560.1127.107.95214.80[14]
      2.0%Dy3+: CeF33.7471.5309.2590.141740.83[17]
      1.0%Dy3+: GdScO30.6500.4594.101.88270.60[34]
      2.0%Dy3+: Gd3Ga5O121.1070.7902.622.07071.40[35]
      2.0%Dy3+: LaF31.7001.3707.009.59080.59[36]

    σem of 1.0%Dy: YAG is close to those of gallate and scandate crystals related value at a similar concentration while it is much smaller than those of sesquioxide and fluoride crystals[13-14,34 -36] respective values. From the σemτ product, it is noticed that Dy: YAG possesses a smaller threshold than Dy3+: Gd3Ga3Al2O12, Dy3+: Gd3Ga5O12, and Dy3+: GdScO3 crystals. Fluoride crystals might have a lower threshold for yellow laser operation but due to adverse factors such as thermal effect and lower mechanical strength, it is difficult to develop high-power lasers[18-19]. η of Dy: YAG declines rapidly with Dy3+ doping content increment, which is a sign of non-radiative transitions existence between Dy3+ ions, so it is not suitable to generate lasing action with Dy: YAG crystal at higher doping levels. Among all crystals, 1.0% Dy: YAG has the largest σem as well as σemτ for 582 nm yellow emission. Among five samples, the 1.0% Dy: YAG crystal also shows an intense fluorescence intensity with the 447 nm excitation with a longer decay time of 0.823 ms, which is close to the previous work[37]. The fluorescence intensity and σem of 2.0% Dy: YAG are slightly less than that of 1.0% Dy: YAG, but 2.0%Dy: YAG has a higher α. Hence, 1.0%Dy: YAG and 2.0%Dy: YAG crystals are the suitable candidates for the generation of yellow laser output.

    2.3 Laser performance

    The continuous wave (CW) yellow laser output was obtained in 2.0%Dy: YAG crystal. Fig. 4(a) shows the laser spectra of Dy: YAG crystal. The central wavelength of the laser is 582.5 nm, and the full width at half maximum is 1.2 nm. Fig. 4(b) shows the relation curve between absorption pump power and output power, and the maximum output power is 166.8 μW. The slope efficiency is calculated to be 0.32%, with the maximum output power of 0.029%. The laser operation threshold is around 535 mW, which is higher than that of Dy3+,Tb3+:LiLuF4 (320 mW)[38]. When the input power exceeds 3382 mW, the output power decreases significantly which is mainly due to the degradation of rare earth ions caused by laser thermal effect. Owing to the laser experiment parameters haven’t been optimized, the laser output power and efficiency are still very low, we are trying to improve the laser output power now.

    Laser spectra (a) and variation of output power with absorbed pump power of 2.0%Dy: YAG crystal (b)

    Figure 4.Laser spectra (a) and variation of output power with absorbed pump power of 2.0%Dy: YAG crystal (b)

    3 Conclusions

    The visible fluorescence features of Dy: YAG crystals with different Dy3+ doping concentrations were analyzed thoroughly. The optimum concentration for yellow emission under 447 nm is 1.0%, and the 4F9/2 level lifetime is calculated to be 0.823 ms. 1.0%Dy: YAG has the largest σem at 582 nm in present work. 2.0%Dy: YAG could also be an alternative crystal for yellow lasing action on consideration of its greater yellow emission intensity and σem, the acceptable lifetime of 4F9/2 level, and higher absorption intensity. Hence, 1.0%Dy: YAG and 2.0%Dy: YAG crystals are potential candidates for yellow laser output. Finally, the CW laser with the maximum output power of 166.8 μW yellow laser operation is obtained based on 2.0%Dy: YAG crystal.

    [6] C KRÄNKEL, D T MARZAHl, F MOGLIA et al. Out of the blue: semiconductor laser pumped visible rare-earth doped lasers. Laser & Photonics Rev., 10:, 10548(2016).

    [8] D UZLU, H ERDÖL, M KOLA et al. The efficacy of subthreshold micropulse yellow laser (577 nm) in chronic central serous chorioretinopathy. Laser Med. Sci., 12:, 981(2020).

    [10] Q S ZONG, Q BIAN, H D MA et al. The research progress of the new sodium beacon laser. Laser Technol., 44:, 404(2020).

    [18] P W METZ, F MOGLIA, F REICHERT et al. Novel Rare Earth Solid State Lasers with Emission Wavelengths in the Visible Spectral Range. Lasers and Electro-Optics Europe, Munich, Germany, 1(2013).

    [27] G S OFELT. Intensities of crystal spectra of rare earth ions. Journal of Chemical Physics, 37:, 511(1962).

    [28] W T CARNALL, P R FIELDS, K RAJNAK. Electronic energy levels in the trivalent lanthanide aquo ions. I. Pr3+, Nd3+, Pm3+, Sm3+, Dy3+, Ho3+, Er3+, and Tm3+. Chemical Physics, 49:, 4424(1968).

    [32] B F AULL, H P JENSSEN. Vibronic interactions in Nd:YAG resulting in nonreciprocity of absorption and stimulated emission cross sections. IEEE.Quantum Elect., 18:, 925(1982).

    [37] S R BOWMAN, N J CONDON, S O’CONNOR et al. Diode-pumped Dysprosium Laser Materials. SPIE Defense, Security, and Sensing, Orlando, Florida, United States(2009).


    Get Citation

    Copy Citation Text

    Jiaxue YANG, Wen LI, Yan WANG, Zhaojie ZHU, Zhenyu YOU, Jianfu LI, Chaoyang TU. Spectroscopic and Yellow Laser Features of Dy3+: Y3Al5O12 Single Crystals [J]. Journal of Inorganic Materials, 2023, 38(3): 350

    Download Citation

    EndNote(RIS)BibTexPlain Text
    Save article for my favorites
    Paper Information


    Received: Jul. 5, 2022

    Accepted: --

    Published Online: Oct. 16, 2023

    The Author Email: WANG Yan (, TU Chaoyang (