High Efficient Emission And The Investigation Of Spectral Parameters Of Ho³⁺ In Low Phonon Energy Heavy Metal Oxide Glasses

Low phonon energy glasses doped with trivalent rare-earth ions are attractive due to theirpotential applications in developing compact solid-state lasers, optical broadband amplifiersand visible display devices. The up-conversion fluorescence and the infrared transitionradiation of rare earth doped glasses have been paid more and more attention. Many trivalentrare earth ions (Er³⁺, Tm³⁺, Ho³⁺, Pr³⁺and Nd³⁺etc.) can be used as the center of absorptionand luminescence, among the rare-earth ions, Ho³⁺ion has become a kind of allure ions due toits unique1.66and2.0m emission. Owing to the shallower penetration depth and the largertissue absorption coefficient of2.0m Ho³⁺solid-state laser, it has been applied inorthopaedics, ophthalmology, neurosurgery, gynecologic, general surgery and digestionmedicine department successfully. Ho³⁺has been paid more and more attention because of itsfavorable energy level structures and the favorable application in infrared and visible region.As is well known, the phonon energy of the host is the most important factor on theluminous efficiency, the smaller maximum phonon energy, the lower non-radiation relaxationrate, while the luminous efficiency will be higher. Of the oxide glasses, the phonon energiesof tellurite and gallate glasses are lower than those in silicate, borate, phosphate glasses, inaddition, maximum phonon energies is lower, refractive index and density are higher of thetellurite and gallate glasses after adding the oxide bismuth, and in the meantime, highemission cross sections will be obtained and the infrared transition radiation of Ho³⁺will berealized efficiently. Based on this consideration, heavy metal tellurite and gallate glasses weredesigned based on traditional tellurite and gallate glasses. Optical and luminescenceproperties of rare-earth ions in bismuth gallate glasses have been studied. The results obtainedare as follows:1. Ho³⁺doped and Ho³⁺/Yb³⁺co-doped low phonon heavy metal tellurite glasses withlarge refractive indices have been designed and fabricated. Based on optical absorption,Judd-Ofelt parameters2,4and6have been derived to be4.373×10^-20,1.906×10^-20and1.451×10^-20cm², respectively. Then the radiative transition probabilities, radiative lifetimes and fluorescence branching ratios were calculated. The efficient infrared emission inHo³⁺/Yb³⁺co-doped bismuth tellurite glass system has been recorded under the pumping of a982nm diode laser and Yb³⁺is considered to be a preferable sensitizer for catching remarkablepumping energy and transferring considerable energy to Ho³⁺. The maximum absorption andcalculated emission cross sections are5.631021cm²at1.95m and6.241021cm²at2.05m,respectively, which is larger than the values in phosphate and fluoride glasses, and isbeneficial in lowing laser threshold, so as to realize efficient laser output of Ho³⁺. Lowmaximum photon energy and high emission cross sections indicate that Ho³⁺/Yb³⁺co-dopedlow phonon bismuth tellurite glasses will be promising infrared laser materials.2. Ho³⁺/Yb³⁺-codoped bismuth gallate glass with high refractive index has beensynthesized. The refractive index was measured by Bewster’s angles using a spectrometer andthe obtained value was2.296. The emission cross-section of Yb³⁺was calculated to be2.109×10^-20cm². Intense two-photon upconversion fluorescence was investigated under theexcitation of a974nm diode laser at room temperature. The upconversion mechanism hasbeen analyzed and Yb³⁺is considered to be a preferable sensitizer for catching enoughpumping energy and transferring considerable energy to Ho³⁺. The characteristic phononenergy, the high-energy phonon density and the strong absorption in the green spectral rangelead to the increasing of the distribution in⁵F₅state, which can increase the spontaneoustransition probability of⁵F₅â†'⁵I₈emission, as a result, the red emission is stronger than thegreen during the upconversion processes.These new phenomena and results of studies provide the theoretical basis and pledge ofnew materials for new types of fluorescent display devices and fabrication of the newupconversion devices.