ABSTRACT
Lanthanides are routinely incorporated into quantum dots to act as down-shifting and up-converting phosphors in display and lighting applications due to their high photoluminescence quantum yields (PLQY). Recent efforts in the field have demonstrated that trivalent lanthanide, Ln(III), incorporated into ZnAl2O4 spinel nanocrystals can achieve PLQYs of 50% for down-shifting nanophosphors using earth abundant materials. The high PLQY is surprising as the Al(III) site in a spinel is centrosymmetric, which should lead to poor performance for these nanophosphors. However, spinels are prone to formation of an admixture of inverse and normal spinel lattices when the cation size ratio is not optimal. Such behavior can produce local cation disorder that can influence the phosphor performance. Herein, we describe the use of Tb(III) as an optical probe to evaluate the fractional population of the inverse and normal spinel structures within TbxZnAl2-xO4. The experimental data exhibits a Tb(III) concentration dependent change in the fractional population that results in a maximum PLQY of 37% with 3.56% Tb(III) incorporation. A decrease in the degree of inversion (cation disorder) leads to larger amounts of the cubic Fd3m phase resulting in the observed photoluminescence behavior. The correlation of NMR, pXRD, and optical methods provides direct insight into the high PLQY behavior for this class of nanophosphor.
ABSTRACT
BACKGROUND: There is disagreement regarding hospital and physician reimbursement fees when DRG codes are used. We have found that physicians and hospitals are rewarded differently depending on the type of insurance coverage - per diem HMO (Health Maintenance Organization) vs public. METHODS: 133 patients were retrospectively analyzed in a single institution. There were 59 privately-insured and 74 publicly-insured patients. Using DRG 288, hospital and surgeon reimbursement rates, complications, length of stay, blood loss and basic demographics were evaluated on all patients. Reimbursement rates were then compared to inpatient hospital costs per case for both open and laparoscopic Roux-en-Y gastric bypass (RYGBP). Statistical analysis used Student's t-test and standard deviation. RESULTS: The 2 groups were similar in terms of age, sex and BMI. There was a large difference in physician reimbursement when comparing public to private insurance (931 US dollars +/-73 vs 2356 US dollars +/-822, P<0.001). Likewise, there was a large difference in hospital reimbursement (public 11773 US dollars +/- 4462 vs private 4435 US dollars +/- 3106, P<0.001). The estimated costs for open gastric bypass was 3179 US dollars vs 4180 US dollars for the laparoscopic bypass. The HMO per diem rate was 1000 US dollars per day. CONCLUSION: There is a relative disincentive for surgeons to treat publicly-insured patients, while there is an incentive for hospitals to treat those patients. The converse is true for the privately-insured patients. This dichotomy will impede the development of new centers and place greater burden on bariatric surgeons to reduce cost by performing the open RYGBP.
