Excitation mechanisms and localization sites of erbium-doped porous silicon

Porous silicon (PS) is doped with erbium by electrochemical anodisation. The penetration of erbium into the PS layer is confirmed by Rutherford backscattering spectroscopy (RBS) and energy dispersive X-ray (EDX) measurements. Efficient green and infrared emissions were observed at room temperature. The investigations are focused on the evolutions versus temperature and pump intensity of the green photoluminescence (PL) corresponding to the ⁴S_3/2 → ⁴I_15/2 transition. It was found that an erbium related level defect can be involved on the excitation and emission processes of erbium. Pump intensity dependent PL studies revealed that for the electrochemical incorporation, most of the Er³⁺ ions are localized inside the Si nanocrystallites and not in stoichiometric SiO₂. The optical cross-section is close to that of erbium in Si nanocrystallites.     

Structure and photoluminescence properties of Er3+-doped TiO2-SiO2 powders prepared by sol-gel method

Er 3+-doped TiO 2-SiO 2 powders are prepared by the sol-gel method,and they are characterized by high resolution transmission electron microscopy (HR-TEM),X-ray diffraction (XRD) spectra,and Raman spectra of the samples.It is shown that the TiO 2 nanocrystals are surrounded by an SiO 2 glass matrix.The photoluminescence (PL) spectra are recorded at room temperature.A strong green luminescence and less intense red emission are observed in the samples when they are excited at 325 nm.The intensity of the emission,which is related to the defect states,is strongest at the annealing temperature of 800 C.The PL intensity of Er 3+ ions increases with increasing Ti/Si ratio due to energy transfer between nano-TiO 2 particles and Er 3+ ions.     

Enhanced emission of Er from alternately Er doped Si-rich Al2O3 multilayer film with Si nanocrystals as broadband sensitizers

Alternately Er doped Si-rich Al₂O₃ (Er:SRA) multilayer film, consisting of alternate Er-Si-codoped Al₂O₃ (Er:Si:Al₂O₃) and Si-doped Al₂O₃ (Si:Al₂O₃) sublayers, has been synthesized by co-sputtering from separated Er, Si, and Al₂O₃ targets. The dependence of Er³⁺ related photoluminescence (PL) properties on annealing temperatures over 700-1100 °C was studied. The maximum intensity of Er³⁺ PL, about 10 times higher than that of the monolayer film, was obtained from the multilayer film annealed at 950 °C. The enhancement of Er³⁺ PL intensity is attributed to the energy transfer from the silicon nanocrystals in the Si:Al₂O₃ sublayers to the neighboring Er³⁺ ions in the Er:Si:Al₂O₃ sublayers. The PL intensity exhibits a nonmonotonic temperature dependence: with increasing temperature, the integrated intensity almost remains constant from 14 to 50 K, then reaches maximum at 225 K, and slightly increases again at higher temperatures. Meanwhile, the PL integrated intensity at room temperature is about 30% higher than that at 14 K.     

溶胶-凝胶法Er2O3薄膜的结构和光学特性

针对稀土Er掺杂Si光源中Er离子掺杂浓度低的问题,采用溶胶-凝胶（Sol-gel）法在Si(100)和SiO2/Si(100)基片上旋涂法制备Er₂O₃光学薄膜,Er离子浓度与以前掺杂方法相比提高了2个数量级.900 ℃热处理获得单一立方结构的Er₂O₃薄膜材料.光致发光（PL）特性研究表明在654 nm波长的激光泵浦下,Er₂O₃薄膜材料获得了1.535 μm的发光峰,并具有较小的温度猝灭1/5.在SiO₂/Si(100)基体上制备的Er2O3薄膜材料的光致发光强度比Si(100)基体上制备的薄膜提高2-3倍.研究结果表明具有强光致发光特性的Er₂O₃薄膜是一种有前景的硅基光源和放大器材料.     

Erbium ion luminescence of silicon nanocrystal layers in a silicon dioxide matrix measured under strong optical excitation

The photoluminescence (PL) spectra and kinetics of erbium-doped layers of silicon nanocrystals dispersed in a silicon dioxide matrix (nc-Si/SiO₂) are studied. It was found that optical excitation of nc-Si can be transferred with a high efficiency to Er³⁺ ions present in the surrounding oxide. The efficiency of energy transfer increases with increasing pumping photon energy and intensity. The process of Er³⁺ excitation is shown to compete successfully with nonradiative recombination in the nc-Si/SiO₂ structures. The Er³⁺ PL lifetime was found to decrease under intense optical pumping, which implies the establishment of inverse population in the Er³⁺ system. The results obtained demonstrate the very high potential of erbium-doped nc-Si/SiO₂ structures when used as active media for optical amplifiers and light-emitting devices operating at a wavelength of 1.5 μm.     

Excitation process and photoluminescence properties of Tb and Eu ions in SnO2 and in SnO2: Porous silicon hosts

Tin oxide (SnO₂)-layers-doped terbium and europium ions are elaborated by the sol-gel method on silicon substrates. After annealing at 500 °C, the transmission electron microscopy revealed a crystallization of tin oxide.The emission properties of rare-earth in SnO₂ are studied systematically against temperature annealing and Tb³⁺ concentration. The PL spectrum is optimal after annealing at 900 °C and the corresponding photoluminescence (PL) decay is nearly exponential, showing that the sample is homogenous and the PL process can be described by two levels system.The concentration effect shows a quenching of the PL intensity for Tb³⁺ concentration above 4%. From the investigation of the decay rate from the ⁷F₅ state within terbium concentration, we show that self-quenching is insured by dipole - dipole interaction. The evolutions of both PL intensity and PL lifetime versus temperature are studied. The PL intensity and PL lifetime are enhanced by deposing SnO₂:Tb³⁺ and SnO₂:Eu³⁺ in porous silicon. We show that an efficient excitation transfer from Si nanocrystallites to RE ions can occur.     

Photoluminescence properties of Er-doped β-FeSi2 grown by ion implantation

Photoluminescence (PL) properties of Er-doped β-FeSi₂ (β-FeSi₂:Er) and Er-doped Si (Si:Er) grown by ion implantation were investigated. In PL measurements at 4.2 K, the β-FeSi₂:Er showed the 1.54 μm PL due to the intra-4f shell transition of ⁴I_13/2→⁴I_15/2 in Er³⁺ ions without a defect-related PL observed in Si:Er. In the dependence of the PL intensity on excitation photon flux density, the obtained optical excitation cross-section σ in β-FeSi₂:Er (σ=7×10⁻¹⁷ cm²) is smaller than that in Si:Er (σ=1×10^-15 cm²). In the time-resolved PL and the temperature dependence of the PL intensity, the 1.54 μm PL in β-FeSi₂:Er showed a longer lifetime and larger activation energies for non-radiative recombination (NR) processes than Si:Er. These results revealed that NR centers induced by ion implantation damage were suppressed in β-FeSi₂:Er, but the energy back transfer from Er³⁺ to β-FeSi₂ was larger than Si:Er.     

Role of Bi ions for Er ions efficient 1.54 μm light emission in Er/Bi codoped SiO2 thin film prepared by sol-gel method

Er/Bi codoped SiO₂ thin films were prepared by sol-gel method and spin-on technology with subsequent annealing process. The bismuth silicate crystal phase appeared at low annealing temperature while vanished as annealing temperature exceeded 1000 °C, characterized by X-ray diffraction, and Rutherford backscattering measurements well explained the structure change of the films, which was due to the decrease of bismuth concentration. Fine structures of the Er³⁺-related 1.54 μm light emission (line width less than 7 nm) at room temperature was observed by photoluminescence (PL) measurement. The PL intensity at 1.54 μm reached maximum at 800 °C and decreased dramatically at 1000 °C. The PL dependent annealing temperature was studied and suggested a clear link with bismuth silicate phase. Excitation spectrum measurements further reveal the role of Bi³⁺ ions for Er³⁺ ions near infrared light emission. Through sol-gel method and thermal treatment, Bi³⁺ ions can provide a perfect environment for Er³⁺ ion light emission by forming Er-Bi-Si-O complex. Furthermore, energy transfer from Bi³⁺ ions to Er³⁺ ions is evidenced and found to be a more efficient way for Er³⁺ ions near infrared emission. This makes the Bi³⁺ ions doped material a promising application for future erbium-doped waveguide amplifier and infrared LED.     

掺饵氢化非晶氧化硅1.54μm发光性质的研究

采用等离子体增强化学汽相沉积技术生长不同氧含量的氢化非晶氧化硅薄膜(a-SiO_{x∶H),离子注入铒及退火后在室温观察到很强的光致发光.当材料中氧硅含量比约为1和 1.76时,分别对应77Ｋ和室温测量时最强的1.54μm光致发光.从15到250Ｋ的变温实验显示 出三个不同的强度与温度变化关系,表明氢化非晶氧化硅中铒离子的能量激发和发光是一个 复杂的过程.提出氢化非晶氧化硅薄膜中发光铒离子来自于富氧区,并对实验现象进行了解 释.氢化非晶氧化硅中铒发光的温度淬灭效应很弱.从15到250Ｋ,光致发光强度减弱约1/2. 关键词： 铒 光致发光 氧含量}     

Population inversion of the energy levels of erbium ions induced by excitation transfer from the semiconductor matrix in Si-Ge based structures

Population inversion of the energy levels of Er³⁺ ions in Si/Si_1?xGe_x:Er/Si (x = 0.28) structures has been achieved due to electron excitation transfer from the semiconductor matrix. An analysis of the photoluminescence kinetics at a wavelength of 1.54 μm shows that up to 80% of the Er³⁺ ions are converted into excited states. This effect, together with the high photoluminescence intensity observed in the structures studied, shows good prospects for obtaining lasers compatible with planar silicon technology.     

退火处理对掺铒氢化非晶硅悬挂键密度和光致荧光的影响

采用磁控溅射技术制备了铒掺杂的氢化非晶硅(a-Si∶H(Er))样品.进一步通过200—500℃温度递增的后退火处理，获得了不同的Si悬挂键(Si-DBs)密度，并在此基础上研究了Si-DBs密度改变对其Er光荧光(Er-PL)的影响.退火温度低于350℃时，Er-PL强度持续增加，但Si-DBs密度的变化显得较复杂；350℃以上时，Er-PL强度随Si-DBs密度的增加而减小.在200—250℃的退火温度范围内，Si-DBs是由于结构弛豫而减少；在250—500℃的退火温度范围内，可能由于Si—H键的断 关键词： 氢化非晶硅 铒掺杂 Si悬挂键 光荧光     

Effective excitation cross section and lifetime of Er<Superscript>3+</Superscript> ions in Si: Er light-emitting diodes fabricated by sublimation molecular-beam epitaxy

A series of Si: Er electroluminescent diode structures is fabricated by sublimation molecular-beam epitaxy. The diode structures efficiently emit at a wavelength of 1.5 μm under conditions of p-n junction breakdown at room temperature. The effective cross section of excitation of Er³⁺ ions with hot carriers heated by the electric field of a reverse-biased p-n junction and the lifetime of Er³⁺ ions in the first excited state ⁴I_13/2 are determined for structures that emit in a mixed breakdown mode and are characterized by the maximum intensity and excitation efficiency of the Er³⁺ electroluminescence.     

Sensitisation of erbium emission by silicon nanocrystals-doped SnO2

SnO₂ thin films undoped and doped with antimony (Sb), erbium (Er) and Si nanocrystals (Si-nc) have been grown on silicon (Si) substrate using sol-gel method. Room-temperature photoluminescence (PL) measurement of undoped SnO₂, under excitation at 280 nm, shows only one broad emission at 395 nm, which is related to oxygen vacancies. The PL of Er³⁺ ions was found to be enhanced after doping SnO₂ with Sb and Si-nc. The excitation process of Er is studied and discussed. The calculation of cross-section suggests a sensitisation of Er PL by Si-nc.     

Photoluminescence characteristics of energy transfer between Er and Bi in Gd2O3: Er, Bi

The phosphors, Bi³⁺- activated Gd₂O₃:Er³⁺, were prepared by sol-gel combustion method, and their photoluminescent properties were investigated under ultraviolet light excitation. The emission spectrum exhibited sharp peaks at about 520, 535, 545, 550 and 559 nm due to (²H_11/2, ⁴S_3/2)→⁴I_15/2 transitions of Er³⁺ ions. The luminescent intensity was remarkably improved by the incorporation of Bi³⁺ ions under 340 nm light excitation, which suggested very efficient energy transfer from Bi³⁺ ions to Er³⁺ions. The introducing of Bi³⁺ ions broadened the excitation band of the phosphor, of which a new strong peak occurred ranging from 320 to 360 nm due to the 6s²→6s6p transition of Bi³⁺ ions. There is significant energy overlap between the emission band of Bi³⁺ ions and the excitation band of Er³⁺ ions. Under 340 nm light excitation, Bi³⁺ absorbed most of the energy and transferred it to Er³⁺. The energy transfer probability from Bi³⁺ to Er³⁺ is strongly dependent on the Bi³⁺ ion concentration. Also, the sensitization effectiveness was studied and discussed in this paper.     

Thermal and optical properties of Er-doped oxyfluorotellurite glasses

Er³⁺-doped oxyfluorotellurite glasses with four different concentrations of Er³⁺ ions have been prepared and investigated their thermal, optical absorption, excitation and luminescence properties. From the DSC spectra, glass transition and onset of crystallization temperatures have been found. Judd-Ofelt intensity parameters have been derived from the absorption spectrum and are in turn used to calculate radiative properties for the important luminescent levels of Er³⁺ ions. The calculated radiative properties are comparable to experimental values. The glasses show intense green and weak red emission under normal excitation with 451 nm. The decrease in emission intensities and lifetimes of the ⁴S_3/2 level with concentration of Er³⁺ ions has been explained as due to energy transfer processes between Er³⁺ ions. The stimulated emission cross-sections and quantum efficiencies of the green and infrared emissions have been determined. The results indicate that the glasses may be suitable for use as a laser medium in making solid-state green laser by normal pumping route and as laser medium and optical amplifier in the 1.5 μm region.     

Temperature-dependent photoluminescence spectra of Er-Tm-codoped Al2O3 thin film

Er-Tm-codoped Al₂O₃ thin films with different Tm to Er concentration ratios were synthesized by cosputtering from separated Er, Tm, Si, and Al₂O₃ targets. The temperature dependence of photoluminescence (PL) spectra was studied. A flat and broad emission band was achieved in the 1.4-1.7 μm and the observed 1470, 1533 and 1800 nm emission bands were attributed to the transitions of Tm³⁺: ³H₄ → ³F₄, Er³⁺: ⁴I_13/2 → ⁴I_15/2 and Tm³⁺: ³F₄ → ³H₆, respectively. The temperature dependence is rather complicated. With increasing measuring temperature, the peak intensity related to Er³⁺ ions increases by a factor of five, while the Tm³⁺ PL intensity at 1800 nm decreases by one order of magnitude. This phenomenon is attributed to a complicated energy transfer (ET) processes involving both Er³⁺ and Tm³⁺ and increase of phonon-assisted ET rate with temperature as well. It should be helpful to fully understand ET processes between Er and Tm and achieve flat and broad emission band at different operating temperatures.     

Er3+离子掺杂钡镓锗玻璃上转换发光机理研究

研究了Er³⁺离子掺杂钡镓锗玻璃的吸收光谱、拉曼光谱和上转换光谱.分析了Er³⁺离子在钡镓锗玻璃中的上转换发光机理.结果表明：玻璃的最大声子能量为828cm^-1，紫外截止波长为275nm.采用800nm和980nmLD激发玻璃样品，在室温下观察到强烈的上转换绿光和红光发射.随着Er³⁺离子浓度的增加，绿光发光强度先增加后减小，而红光发光强度呈单调递增趋势.能量分析表明：800nmLD激发产生的绿光主要源于Er³⁺离子4I_13/2能级的激发态吸收过程；红光发射主要源于Er³⁺离子4I_13/2能级与4I_11/2能级之间的能量转移过程.980nmLD激发产生的绿光主要源于Er³⁺离子4I_11/2能级之间的能量转移过程；而红光发射主要源于Er³⁺离子4I_13/2能级与4I_11/2能级之间的能量转移过程和4I_13/2能级的激发态吸收过程.通过量子效率分析，发现采用800nmLD激发Er³⁺离子掺杂浓度为1mol% 的样品时，上转换绿光发光效率最高. 关键词： 上转换发光机理 3+离子掺杂')" href="#">Er³⁺离子掺杂 钡镓锗玻璃     

Long lifetime and efficient emission from Er ions coupled to Si nanoclusters in Si-rich SiO2 layers

Reactive magnetron co-sputtering of two confocal SiO₂ and Er₂O₃ cathodes in argon-hydrogen plasma was used to deposit Er-doped Si-rich SiO₂ layers. The effects of the deposition conditions (such as RF power applied on each cathode and total plasma pressure) and annealing treatment (temperature and duration) on structural, compositional and photoluminescence (PL) properties of the layers were examined. It was found that a significant enhancement of both Er³⁺ PL intensity and emission lifetime up to 9 ms have been reached through monitoring of the conditions of both deposition process and annealing treatment. The effective absorption cross section and the fraction of Er ions coupled to Si clusters were analyzed. It was shown an increase of the fraction of Er³⁺ ions coupled to Si up to 11%.     

Photoluminescence from Er-doped silicon rich oxide thin films

 Photoluminescence (PL) properties of Er-doped silicon rich oxide thin films deposited on Si substrate by co-evaporation of silicon monoxide and Er under different atmospheres are investigated. The samples exhibit luminescence peak at 1.54 μm which could be assigned to the recombination in intra-4f Er³⁺ transition. PL shows that this transition is highest when ammonia atmosphere is used during deposition followed by an annealing temperature at 850 °C in 95% N₂+5% H₂ gas (forming gas). In fact, we believe that the presence of the N atoms around Er ions increases the intensity of the 1.54 μm luminescence.     

Upconversion luminescence from Er-N codoped of ZnO nanowires prepared by ion implantation method

Nitrogen and erbium co-doped of ZnO nanowires (NWs) are fabricated by ion implantation and subsequent annealing in air. The incorporation of Er³⁺ and N⁺ ions is verified by energy dispersive X-ray spectroscopy (EDS) and Raman spectra. The samples exhibit upconversion photoluminescence around ∼550 nm and ∼660 nm under an excitation at 980 nm. It is discovered that the N-doped can drastically increase the upconversion photoluminescence intensity by modifying the local structure around Er³⁺ in ZnO matrix. The enhancement of the PL intensity by the N-doped is caused by the formation of ErO_6−xN_x octahedron complexes. With the increase of the annealing temperature (T_a), the Er³⁺ ions diffuse towards the surface of the NWs, which benefits the red emission and evokes the variation of intensity ratio owing to the existence of some organic groups.