Rare Earth Doped Laser Crystal Study Of The Radiation Mechanism Of Ion Luminescence Properties

Non-radiative mechanisms in rare-earth ions doped crystals were researched from two aspects:"non-radiative interaction between ions and host material" and "non-radiative interaction between doped ions".The main research includes two parts.Upconversion(UC),infrared emission(near 1540 nm),and the temperature dependent luminescence properties of Er³⁺-yb³⁺ co-doped Gd₂SiO₅(GSO),Lu₂SiO₅ (LSO) and(Lu_0.5Gd_0.5)₂SiO₅(LGSO) laser crystals are researched.The UC emission bandwidth is very broad containing multiple peaks,and the normalized UC efficiencies can reach up to 0.58×10^-3 cm²/W(GSO,green emission),1.16×10^-3 cm²/W(GSO,red emission),0.89×10^-3 cm²/W(LSO,green emission),1.04×10^-3 cm²/W(LSO,red emission),0.83×10^-3 cm²/W(LGSO,green emission),and 0.93×10^-3 cm²/W(LGSO,red emission).Broad infrared emission(1540 nm) in Er³⁺-yb³⁺ co-doped LSO and LGSO crystals are measured under excitation of 975 nm.The emission cross-section near 1540 nm can reach up to 0.793×10^-20 cm²(LSO) and 0.994×10^-20 cm²(LGSO),respectively.The temperature-dependent luminescence properties of these crystals are also investigated.Upconversion near The rate equations considering the multi-phonon assistant relaxations(MPR) and multi-phonon assistant energy transfer(MPET) as the temperature-dependent functions were adopted to analyze the results.Our study indicates that Er³⁺-Yb³⁺ co-doped GSO,LSO and LGSO crystals are promising gain media for developing the solid-state 1.5μm optical amplifiers and tunable UC lasers.Upconversion blue emissions of Tm³⁺ ions doped NaY(WO₄)₂(NYW) crystals are investigated with different doping concentration and three different near-infrared pump mechanisms(800 nm pump Tm³⁺:NYW,800 nm pump Tm³⁺-Yb³⁺:NYW,980 nm pump Tm³⁺-Yb³⁺:NYW).The dependence of upconversion efficiency on ion concentration and pump mechanisms is analyzed from the scope of concentration quenching effect.Four cross relaxation(CR) processes:³H₅ +¹G₄→³H₆ +¹D₂,³H₅+ ³H₅→³H₆ +³F₃,¹G₄ +³H₆→³F₄ +³F₃,¹G₄ +³H₆→³F₃ +³F₄,which influence the upconversion dominantly in Tm³⁺ heavy-doped system,are demonstrated theoretically and experimentally.The results indicate that Yb³⁺ ions can weaken the concentration quenching effect of Tm³⁺ ions significantly so that the blue emission efficiency can be enhanced by one order of magnitude.At the same time,the wavelength of pump source also has considerable influence on both the population of some crucial energy levels and the upconversion mechanism.Experiments show that the upconversion blue emission in Tm³⁺/Yb³⁺ co-doped NaY(WO₄)₂ crystal under 980 nm LD excitation is the most intensive of these three different near-infrared pump mechanisms.The conclusions are confirmed by spectra measurements and calculations of Judd-Ofelt(J-O) theory and Miyakawa -Dexter's(M-D) theory.Our work shows that both "non-radiative interaction between ions and host material"(MPR and MPET) and "non-radiative interaction between ions"(CR) are the improtant influencing factors to the luminescence properties.The rules of these non-radiative energy transfer mechanisms can be investigated and found,and they can be controlled to be benefitial to some specifical radiation.