The LiYF4single crystals singly doped Ho3tand co-doped Ho3t,Pr3tions were grown by a modified Bridgman method.The JuddeOfelt strength parameters(U2,U4,U6)of Ho3twere calculated according to the absorption spectra and the JuddeOfelt theory,by which the radiative transition probabilities(A),fluorescence branching ratios(b)and radiative lifetime(srad)were obtained.The radiative lifetimes of5I6and5I7levels in Ho3t(1 mol%):LiYF4are 10.89 and 20.19 ms,respectively,while 9.77 and 18.50 ms in Ho3t/Pr3tdoped crystals.Hence,the sradof5I7level decreases significantly by introduction of Pr3tinto Ho3t:LiYF4crystal which is beneficial to the emission of 2.9 mm.The maximum emission cross section of Ho3t:LiYF4crystal located at2.05 mm calculated by McCumber theory is 0.51 10 20cm2which is compared with other crystals.The maximum emission cross section at 2948 nm in Ho3t/Pr3tco-doped LiYF4crystal obtained by Fuchtbauere Ladenburg theory is 0.68 10 20cm2,and is larger than the value of 0.53 10 20cm2in Ho3tsingly doped LiYF4crystal.Based on the absorption and emission cross section spectra,the gain cross section spectra were calculated.In the Ho3tions singly doped LiYF4crystal,the gain cross sections for 2.05 mm infrared emission becomes positive once the population inversion level reaches 30%.It means that the pump threshold for obtaining 2.05 mm laser is probably lower which is an advantage for Ho3t-doped LiYF42.05 mm infrared lasers.The calculated gain cross section for 2.9 mm mid-infrared emission does not become positive until the population inversion level reaches 40%in Ho3t/Pr3t:LiYF4crystal,but 50%in Ho3tsingly doped LiYF4crystal,indicating that a low pumping threshold is achieved for the Ho3t:5I6/5I7laser operation with the introduction of Pr3tions.It was also demonstrated that Pr3tion can deplete rapidly the lower laser Ho3t:5I7level and has influence on the Ho3t:5I6level.The Ho3t/Pr3t:LiYF4crystal may be a potential media for 2.9 mm mid-infrared laser.
Super-broadband near-infrared(NIR)emission from 1100 nm to 1600 nm is observed in Bi-doped titanate glasses at the excitation of 808 nm laser diode(LD).The effects of Bi content on the optical spectra are investigated.It is also found that the Bi-related emission intensity can be enhanced by Yb3+co-doping at the excitation of 980 nm LD.It should be ascribed to the energy transfer from Yb3+to active Bi ions.The energy transfer processes are studied based on the Inokuti-Hirayama(I-H)model,and the energy transfer of electric dipole-dipole interaction is confirmed to be dominant in Bi/Yb co-doped glasses.
Optical absorption,excitation,and fluorescence were investigated in Eu ion-doped CdWO4 single crystal grown by a modified Bridgman method.The results indicate that Eu2+ and Eu3+ ions coexist in CdWO4 crystal and an energy transfer occurs between these Eu2+ and Eu3+ ions.When the crystal is excited by 266-nm light,the energy corresponding to the 4f65d to 8S7/2 transition of Eu2+ ions results in the excitation of the Eu3+ ions to the 5DJ level.The effect on fluorescence of annealing in oxygen at various temperatures was investigated.The excitation intensity of Eu2+ ions at 266 nm decreases as annealing temperature increases from 300 K to 1073 K,but it remains at a certain equilibrium level when the annealing temperature is further increased.
A Dy3+-doped LiYF4 single crystal capable of generating white light by simultaneous blue and yellow light emission of phosphorescent centers is produced.Chromaticity coordinates and photoluminescence intensity vary with excitation wavelength.Under 350,365,and 388 nm excitation,the crystal shows excellent white light emission.The most efficient wavelength for white light is 388 nm.The CIE coordinates are x=0.316 and y =0.321,and the color temperature(Tc) is 6 368 K.These results indicate that the studied crystal is a potential candidate for ultraviolet light-excited white light-emitting diodes.
