Abstract
The high phonon energy and short infrared cut-off wavelength of conventional oxide glass (or crystal) hosts are the limitations to achieve mid-infrared (MIR, λ≥2.5μm) luminescence. In present study, the luminescence performance of low phonon and non-conventional TeO2-TiO2-La2O3-based glass (TTL) host doped with Ho3+ and Ho3+/Yb3+ has been investigated, for visible to MIR range. The MIR emission band with peak at 2.88μm (Ho3+:5I6→5I7) and NIR band at 2.04μm (Ho3+:5I7→5I8) has been realized from Ho3+ singly doped TTL glass due to low phonon energy and extended transmission window of the host. Intensity of MIR and NIR emission bands have enhanced significantly in Ho3+/Yb3+: TTL glass under Yb3+ excitation, signifying an efficient Yb3+→Ho3+ energy transfer. The Judd-Ofelt analysis, on Ho3+ absorption characteristics reveals relatively better radiative transition probability (34.4s−1) and branching ratio (10.5%), which is associated to Ho3+:5I6→5I7 transition. The effective bandwidth of 2.88μm emission band is 180nm, with stimulated emission cross-section is 4.26×10-21cm2 and its gain bandwidth has been evaluated as 7.67×10-26cm3. For 2.04μm (Ho3+:5I7→5I8) emission band, the effective bandwidth of 160.5nm and gain bandwidth of 7.26×10-26cm3 have been accomplished. The non-resonant Förster-Dexter method has been applied to Ho3+/Yb3+: TTL glass on emission (donor, Yb3+) and absorption (acceptor, Ho3+) cross sections. The evaluated donor-donor (CDD) and donor-acceptor (CDA) energy transfer micro-parameters are 1.02×10-38 and 5.88×10-41cm6/s respectively while, maximum energy transfer efficiency has been 80%. In concise, Ho3+/Yb3+ codoped TeO2–TiO2–La2O3 glass host has revealed its potential for MIR to NIR photonic applications.
Highlights
MIR lasers operating at 2–5μm are of huge significance as various gas-groups and hazardous chemicals are having their absorption bands around this wavelength range – making it useful in environmental pollution monitoring, chemical sensing, medical diagnostics, military countermeasures, and light detection and ranging (LIDAR) applications.1–3 Currently, Optical Parametric Oscilloscope (OPO) and Quantum Cascade Lasers (QCL) are commercially available as MIR source.4 the requirement of highly coherent monochromatic excitation source and significant dissipation of input power, have been the major limitations which, prevent their use in comparatively high power applications.4 cost-effective broadband MIR source with high output power is a challenge to accomplish
IR edge for 50% transmittance is realized at 5.5 μm, signifying the capability of MIR luminescence from TeO2TiO2-La2O3-based glass (TTL) glass
The lifetime of 1006nm of 0.1mol% Yb2O3 doped TTL glass has been evaluated as 434μs, which has been considered as τ0 for present situation
Summary
MIR lasers operating at 2–5μm are of huge significance as various gas-groups and hazardous chemicals are having their absorption bands around this wavelength range – making it useful in environmental pollution monitoring, chemical sensing, medical diagnostics, military countermeasures, and light detection and ranging (LIDAR) applications. Currently, Optical Parametric Oscilloscope (OPO) and Quantum Cascade Lasers (QCL) are commercially available as MIR source. the requirement of highly coherent monochromatic excitation source and significant dissipation of input power, have been the major limitations which, prevent their use in comparatively high power applications. cost-effective broadband MIR source with high output power is a challenge to accomplish. Glasses doped with suitable lanthanide ion can be a reasonable solution to achieve cost effective, broadband and high power MIR lasers.4 In this regard, most conventional SiO2-based glass possesses robust structure, thermal stability, mechanical and chemical durability, but their maximum phonon energy is ∼1100cm-1 and infrared cutoff wavelength being at 2.5μm, which limits their working wavelength range from visible to NIR (0.3μm–2.2μm).. TeO2-based glasses having suitable phonon energy (650–750cm-1), extended transmission window (0.4–6μm), high solubility of rare-earth ions (∼15mol%), considerable glass transition temperature (350–450○C), thermal stability (60–120○C), refractive index (n ∼2.1), mechanical durability and zero dispersion wavelength (λZDW ∼2.3μm) These glass hosts are most promising for MIR photonic applications.. Oxide-based TTL glass codoped with suitable RE3+ ions is a promising host to achieve broadband MIR and NIR luminescence with low threshold values for photonic applications
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