Optical Spectroscopy of the $Nd^{3+}$ Luminescence Centres in the $Sr_{4}B_{14}O_{25}:Nd$ Crystal

Optical absorption, emission and luminescence kinetics of $Nd^{3+}$ centres in the new borate crystal with $Sr_{4}B_{14}O_{25}:Nd$ (Nd content 0.2 wt.%) composition are investigated and analysed. The oscillator strengths ($P_\text{theor}$ and $P_\text{exp}$) for observed absorption transitions and phenomenological intensity parameters $Ω_t$ ($Ω_2$=1.59×$10^{-20} cm^{-1}$, $Ω_{4}$ = 2.06 × $10^{-20} cm^{-1}$, and $Ω_{6}$ = 2.28 × $10^{-20} cm^{-1}$ were calculated based on the standard Judd-Ofelt theory. Using $Ω_t$ parameters the radiative transitions rates $(W_{r})$, branching ratios (β) and radiative lifetime $(τ_{rad})$ for $Nd^{3+}$ centres in the $Sr_{4}B_{14}O_{25}:Nd$ crystal were calculated and analysed. Measured lifetime ($τ_{exp}$ = 105 and 93 μs at T = 10 and 300 K, respectively) is compared with this calculated ($τ_{rad}$ = 331 μs) and quantum efficiency for $Nd^{3+}$ centres from $\text{}^{4}F_{3//2}$ emitting level in the $Sr_{4}B_{14}O_{25}:Nd$ crystal is estimated (η ≅ 30%). Incorporation peculiarities and local structure of $Nd^{3+}$ luminescence centres in the $Sr_{4}B_{14}O_{25}$ crystal and corresponding glass with $4SrO-7B_{2}O_{3}$ composition are discussed on the basis of referenced X-ray diffraction data and presented results.